Progress in Physical Organic Chemistry, Volume 10
Editors Andrew Streitwieser, Jr. Robert W. Taft JOHN WILEY & SONS
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Progress in Physical Organic Chemistry, Volume 10
Editors Andrew Streitwieser, Jr. Robert W. Taft JOHN WILEY & SONS
Progress in
PHYSICAL ORGANIC CHEMISTRY VOLUME 10
Progress in
PHYSICAL ORGANIC
CHEMISTRY VOLUME 10
Editors
ANDREW STREITWIESER JR.,
Department of Chemistry University of California, Berkeley, California
ROBERT W. TAFT, Department of Chemistry University of GIifornia, frvine, California
1973 A N INTE RSCIEN CE@ P U B L I C ~ T I ON
JOHN WILEY &SONS,
New York
London
*
Sydney
Toronto
An Interscience@ Publication Copyright 0 1973, by John Wiley & Sons, Inc. All rights reserved. Published simultaneously in Canada.
No part of this book may be reproduced by any means, nor transmitted, nor translated into a machine language without t k written permission of the publisher.
Library of Congress Catalog Card Number: 63-19364 ISBN 0-471-83356-8 Printed in the United States of America 1 0 9 8 7 6 5 4 3 2 1
Introduction to the Series
Physical organic chemistry is a relatively modern field with deep roots in chemistry. The subject is concerned with investigations of organic chemistry by quantitative and mathematical methods. The wedding of physical and organic chemistry has provided a remarkable source of inspiration for both of these classical areas of chemical endeavor. Further, the potential for new developments resulting from this union appears to be still greater. A closening of ties with all aspects of molecular structure and spectroscopy is clearly anticipated. The field provides the proving ground for the development of basic tools for investigations in the areas of molecular biology and biophysics. The subject has an inherent association with phenomena in the condensed phase and thereby with the theories of this state of matter. The chief directions of the field are: (a) the effects of structure and environment on reaction rates and equilibria; (b) mechanism of reactions; and (c) applications of statistical and quantum mechanics to organic compounds and reactions. Taken broadly, of course, much of chemistry lies within these confines. The dominant theme that characterizes this field is the emphasis on interpretation and understanding which permits the effective practice of organic chemistry. The field gains its momentum from the application of basic theories and methods of physical chemistry to the broad areas of knowledge of organic reactions and organic structural theory. The nearly inexhaustible diversity of organic structures permits detailed and systematic investigations which have no peer. The reactions of complex natural products have contributed to the development of theories of physical organic chemistry, and, in turn, these theories have ultimately provided great aid to the elucidation of structures of natural products. Fundamental advances are offered by the knowledge of energy states and their electronic distributions in organic compounds and the relationship of these to reaction mechanisms. The development, for example, of even an empirical and approximate general scheme for the estimation of activation energies would indeed be most notable. The complexity of even the simplest organic compounds in terms of physical theory well endows the field of physical organic chemistry with the frustrations of approximations. The quantitative correlations employed in this field vary from purely empirical operational formulations to the approach of applying physical principles to a workable model. The most common procedures V
vi
INTRODUCTION TO THE S1:RIHS
have involved the application of approximate theories to approximate models. Critical assessment of the scope and limitations of these approximate applications of theory leads to further development and understanding. Although he may wish t o be a disclaimer, the physical organic chemist attempts to compensate his lack of physical rigor by the vigor of this efforts. There has indeed been recently a great outpouring of work in this field. We believe that a forum for exchange of views and for critical and authoritative reviews of topics is an essential need of this field. It is our hope that the projected periodical series of volumes under this title will help serve this need. The general organization and character of the scholarly presentations of our series will correspond to that of the several prototypes, e.g., Advances in Enzymology, Advances in Chemical Physics, and Progress in Inorganic Chemistry. We have encouraged the authors to review topics in a style that is not only somewhat more speculative in character but which is also more detailed than presentations normally found in textbooks. Appropriate to this quantitative aspect of organic chemistry, authors have also been encouraged in the citation of numerical data. It is intended that these volumes will find wide use among graduate students as well as practicing organic chemists who are not necessarily expert in the field of these special topics. Aside from these rather obvious considerations, the emphasis in each chapter is the personal ideas of the author. We wish to express our gratitude to the authors for the excellence of their individual presentations. We greatly welcome comments and suggestions on any aspect of these volumes. ANDREWSTREITWIESER, JR. ROBERTW. TAFT
Contents
A Generalized Treatment of Substituent Effects in Benzene Series. A Statistical Analysis by the Dual Substituent Parameter Equation. BY S. EHR E N SO N , Department of Chemistrv, Brookhaven National Laboratory, Upton, Long Island, New York; R. T. C. BROWNLEE, Department of Chemistry, La Trobe University, Bundowa, Victoria, Australia; R. W. TAFT,Department of Chemistry, University of California, Irvine, California . . . . . . . . . . . . 1 Substituent Effects in Nonaromatic Unsaturated Systems. BY M. C H A R T O N , Department of Chemistry, Pratt Institute, Brooklyn, NewYork . . . . . . . . . . . . . . . . . 81 Vinyl and Allenyl Cations. BY P. J. S T A N G , Department of Chemistry, . . . . . 205 The University o f Utah, Salt Lake City, Utah Physical Properties and Reactivity of Radicals. BY R. Z A HR A D N I K A N D P. C A R S K Y , Institute of Physical Chemistry, Czechoslovak . . . . . 327 Academy of Sciences, Prague, Czechoslavakia Probing the Active Sites of Enzymes with Conformationally Restricted Substrate Analogs. BY G. L. K E N Y O NA N D J. A. FEE, Department of Chemistry, University o,f California, Berkeley, California . 381 The Enthalpy-Enthropy Relationship. BY 0. E X N E R , J. Heyrovsky Institute of Polarography, Czechslovak Academy of Sciences, Prague, . . . . . . . . . . . . . . . 41 1 Czechoslovakia Author Index
. . . . . . . . . . . . . . . . . 483
Subject Index
. . . . . . . . . . . . . . . . . 501
Cumulative Index,Volumes 1-10
. . . . . . . . . . 505
vii
Progress in
PHYSICAL ORGANIC CHEMISTRY VOLUME 10
A Generalized Treatment of Substituent Effects in the Benzene Series. A Statistical Analysis by the Dual Substituent Parameter Equation ( 1 ) By S . Ehrenson. R . T . C . Brownlee. and R . W . Taft Contribution from the Brookhaven National Laboratory. Upton. N e w York. 11973. and the Department of Chemistry. University of California. Irvine. California. 92664
CONTENTS
I.
I1.
I11.
IV.
Introduction . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . A . U R (BA type) Values . . . . . . . . . . . B. ak (A type) Values . . . . . . . . . . . . C. &Values . . . . . . . . . . . . . . D . rn-Substituent Effects . . . . . . . . . . . E . uk Values . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . A . Regarding Fittings by Equation ( I ) . . . . . . . B . Pi Delocalization Parameters and their Interpretations . . 1. The u& Scale . . . . . . . . . . . . 2. The OR(BA) Scale . . . . . . . . . . . 3 . The u k Scale . . . . . . . . . . . . . 4. T h e o k Scale . . . . . . . . . . . . . C. ConcerningoR TypeandValuesofthepR Parameter . . D . Concerning the Separation of I and R Effects . . . . E . Variables Affecting h . . . . . . . . . . . F . Ionization of Phenols in Water . . . . . . . . G. Regarding Independent Generation of or and uR Parameters H . “Secondary” OR Values . . . . . . . . . . I . Additional Applications . . . . . . . . . . J . Solvent Effects on pinand pfin Benzoic Acid Ionization . K . Ortho Substituent Effects . . . . . . . . . . Summary . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . References . . . . . . . . . . . . . .
I
. . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .
.
. . . . . . . . . . .
.
. .
. . . . .
. . . . .
. . . . . . . . . .
. . . . .
2 4 4 13 20 28 31 35 35 39 42 42 43 43 44 47 48 50 53 53 55 59 59 64 78 78
2
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
I. INTRODUCTION In this chapter, we report the results of a critical statistical reexamination of substituent effects in the benzene series (2). This investigation has uncovered new basic facts in support of both traditional and new insights. Of particular importance is the demonstration that a practical means of correlation may be achieved for data of a very broad scope with retention of relatively high precision. The treatment is presented in full and applications and their significances are discussed. The thrust of the argument is based upon the fact that no classes of substituents have been arbitrarily neglected: i.e., conclusions are drawn from data sets containing a full range of substituent electronic properties. The analysis of substituent effects in the naphthalene series was carried out along similar lines (2p) and served to prompt this reexamination of the benzene series data. The dual substituent parameter treatment attributes substituent effects to an additive blend of polar (Z) and pi delocalization ( R ) effects, each of which may be represented as a up product (3): log(k/k&, or other substituent property,P=Ii+Ri=urd+oRpk.
(1)
4
The susceptibility or mixing coefficients, and pk, depend upon the position of the substituent (indicated by the index, i) with respect to the reaction (or detector) center, the nature of the measurement at this center, and the conditions of solvent and temperature. It has been held that the qscale of polar effects has wide general applicability (4), holding for substituents bonded to an sp2 or sp3 carbon atom ( 5 ) and, perhaps, to other elements (6). The UR scale, however, has been thought to be more narrowly defined (7), holding with precision only for systems of analogous pi electronic frameworks (i.e., having a dependence on reaction type and conditions, as well as on position of substitution). The limits of eq. (1) may be represented as follows:
P' urpi, -+
as x
-+
O
and
P
-+
u R p i , as X
-+
w,
where X
pR/pI
Several approximately characterized values of single substituent parameter treatments are defined by finite values of A: i.e.,
u(,,,) -tP/pi, as A
-+
.4
U -( P~) o ~ + - + P /ap s hi ,- + 1.0
Swain and Lupton (2q) have recently presented a modified form of the dual substituent parameter treatment. In this treatment, the ur parameters were
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
3
adopted but placed on a readjusted scale. A single universal scale of resonance or pi delocalization parameter ( R ) was proposed which is claimed t o have equal or nearly equal precision of fit when applied generally. This latter proposal runs contrary to earlier thought (2e, f ) and, indeed, clearly is not supported by the present critical analysis. Specifically, statistical evidence is presented herein which supports the basis for at least four distinct scales of pi delocalization effects (u:, O R ,u; , and u i ) , each of which gives excellent precision within “limited generality.” The utility of these scales in discriminating between reaction types, transition-state structures, and reaction conditions is demonstrated and applications are discussed in this and in subsequent papers of the series. Experience has shown that correlations of good precision are those for which SD/RMS = f Q . l , where SD is the root mean square of the deviations and Rh4S is the root mean square of the data P i s . SD is a measure equal to, or approaching in the limit, the standard deviation in parameter predetermined statistics, where a large number of data points determine a small number of parameters. In a few series, RMS is so small that even though SD appears acceptable, f values do exceed . l . Such sets are of little significance pro or can. Evidence has been presented (2p) that this simple f measure of statistical precision is more trustworthy in measuring the precision of structure-reactivity correlations than is the more conventional correlation coefficient. When comparisons are to be drawn among scales derived with different criteria of physical validity, we believe this point to be especially appropriate. The SD is the explicit variable in the least-squares procedure, after all, while the correlation coefficient is a deriva!ive providing at best a non linear acceptability scale, with good and bad correlations often crowded in the range .9-1.0. The present work further provides strong confirmation of this conclusion. A valid UR scale (by our criteria) is one that on application of eq. (1) meets the condition f Q .I in a generalized manner not realized by other scales. A factor of two or greater in the SD for a reaction series (for f values greater than .03)is considered a particularly significant difference. Both the numbers and kinds of substituent data within a series are especially critical. For defining OR scales, we have considered only series data for which at a given position (ortho, meta, or para) the following substituents are available: N(CH&, NH2, or OCH3 (any two of these); any two t R substituents (CF3, C02R, CH3C0, CN, NO2); H and CH3 (both); any two halogens (but not both C1 and Br). This minimal basis set is required to minimize real or accidental correlations between substituent q and UR values. Such a minimal basis set offers substantial assurance of a critical analysis by eq. (1). Application of eq. (1) to series data containing less than the minimal basis set can be subject to uncertainty, if indeed not totally misleading results, depending upon the adequacy of the substituents included. We believe this important limitation has not been adequately recognized in previous treatments.
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
4
11. RESULTS
A. OR (BA type) Values The ionization of benzoic acids in water at 25" was used by Hammett as the standard reaction for the original crp treatment (2a). This reaction and several analogous reactions, e.g., ionization and ester saponification rates of benzoic acids, cinnamic acids, and phenylpropiolic acids, gives up correlations of relatively high precision. Taft and Lewis classified such reactions in an A category (20. Reexamination of these A reactions, as well as additional analogous data which have become available subsequently, provided eight reaction series of data of apparently comparable reliability. In the para position, each of these sets of data meets the necessary condition of a minimal basis set TABLE I Values of
UI
UI
and UR(BA) aR (BA)
n
- .83
6 8 6 8 2 3 8
~
-N(CH 3 ) 2 -NH, -NHCOCH, -OCH, -OC,H, -SCH, -CH -C€.H, -F -c1 -Br -1
-H -Si(CH J, -SOCH, -scF', -SOU -SF,
-CF, -SO,CH -CO,R -CN -NO, -COCH,
.06 .12 .26 .21 .38 .23 -.04 .10
.so .46 .44 .39
.oo -.lo
-.82 -.36 -.61
-.55a -.32 -.11 -.11 -.45 -.23 -.19 -.16
.oo .06
SO
.oo
.42 .64
.04 .08 .06 .08 .I 2 .14 .13 .15 .16
.51
.45 .59 .30 .56 .65 .28
a Value defined by reaction 8 only, cj: discussion
4 1 8 1 6 8 3 3 1 1 1
3 4 6 8 8 5
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
5
(temperature variation alone has not been considered a sufficient condition for distinguishing separate reaction series). The para substituent effect data for these eight reactions were best fitted to eq. (1) by full least-squares methods (21) to generate the “best” OR values for the benzoic acid (BA) type. The statistical methods described previously (21) have been used throughout this study. In addition to eq. (l), the following conditions were imposed upon these data: (a) the q s e t given in Table I (8); (b) the standard (classical) reaction conditions pf’ = pfi = 1.OOO for reaction 1 , the ionization of benzoic acids in water at 25” (note that h = 1.OOO was not imposed on any reaction series other than 1). With these constraints, a set of UR(BA) parameters was obtained for optimum fits to the eight basis sets of data (SD = .039 or 5% of RMS = .73 for 116 data points). It was found, however, that there was no serious loss in precision if certain UR(BA) parameters were modified by .01 to .03 units in order to keep invariance of parameters, if possible, among all of the OR scales of Table V. This modified set of UR ( B A ) was adopted as listed in Table I. The eight basis sets are fitted with the parameters of Table I to SD = .043, or 6% of RMS. Table I1 lists the values of pf, p i , hp = /&, n, SD, and f obtained with Table I parameters for each of the eight reactions. All neutral substituents were treated for which a urvalue was available from at least one aliphatic series reaction and a log (KP/Ko)value for one of the basis set reaction series. The final figure given in Table I1 is the p value obtained from the Hammett u values listed by Richie and Sager (2m) (from the single substituent parameter treatment). The maximum uncertainty in the UR values of Table I is estimated to be k.02 from the ratio of the SD of fit to the RMS of PR values of Table 11. Data for other p-substituted benzene side-chain reactions are fitted by eq. (1) using the UI and OR values of Table I with widely varying precision measures. However, precision of fit comparable to that achieved for the eight basis set reactions of Table I1 is obtained (only) with recognizable analogs of the para BA type. Other reaction types are fitted generally with values of f=SD/RMS greater by factors of two or more than the -6% level achieved by the para BA type (cf. subsequent Tables VII, IX, XII, XIV). In Table 111 are shown values of p f , p$ , hP, n, SD, f and Hammett p values obtained for additional para BA type reaction series which contain data for sufficient numbers ( n ) and kinds of substituents to provide a reasonably critical analysis. We d o not believe, however, that the analysis is as critical for sets which d o not meet the minimal requirements for a basis set. The reaction series are segregated according to type of measurement: equilibrium, rate, and fluorine nmr (F-nmr) shift. Any data set in Table I11 and in all tables hereafter (other than designated basis sets) which meets our minimal basis set criterion is indicated by an asterisk.
PI
OI
Reaction
1.355
1.976 2.222
.84
1.440
1.717
2.539
.75
1.311
1.750
.87
.69 16
9
14
14
10
.87
.947
1.084
14
20 19
n
.79
1.213
1.536
I .O1 .8 I
AP
1.003 1.272
P!4
,997 1.564
P';
.O 3
.04
.032
.047
,073
.052
.04 .06
.058
.03
2.364
I .798
1.589
1.503
1.045
1.359
.038
.02
P
1.002 1.407
P . I 19 .064
.05 .05
SD
1. (a) McDaniel, D. H., and H. C. Brown, J. Org. Chem., 23, 420 (1958); (b) Fischer, A,, B. R. Mann, and J. Vaughan,J. Chem. SOC.,1093 (1961). 2. (a) Roberts, J. D., et al., J. Am. Chem. SOC., 71, 2923 (1949); 72, 408, 628 (1950); 73, 2181 (1951); 75, 2267 (1953);(b) Bordwell, F. C., et ol., J. Am. Chem. SOC., 74, 1058 (1952); 78, 854 (1956); 79, 717 (1957); (c) Fawcett, F. S., and W. A. Sheppard,J. Am. Chem. Soc., 87, 4341 (1965); (d) Sheppard, W. A., J. Am. Chem. Soc., 84,3072 (1962); 85, 1314 (1963); 87, 2410 (1965);(e) Exner, O., and J. Lakomy, Coll. Czech. Chem. Commun., 35, 137 (1970). 3. Wepster, B. M., private communication. 4. Wepster, B. M., private communication. 5. Wepster, B. M.,private communication. 6. (a) Simon, W.,A. Morihofer, and E. Heilbronner, Helv. Chim. Act., 40, 1918 (1957); (b) Exner, O., and I. Jonas, Coll. Czech. Chem. Commun.,27, 2296 (1962); (c) Exner, O., Coll. Czech. Chem. Commun., 31, 65 (1966); (d) Kolfus, K., M. Vecera, and 0. Exner, Coll. Czech. Chem. Commun., 35, 1195 (1970); (e) Exner, O., and I. Lakomy, Coll. Czech. Chem. Commun.,35, 1371 (1970). 7. Davis, M.M., and H. B. Hetzer, J. Res. Natl. Bur. Standards, 60, 569 (1958). 8. (a) cf. Jaffk, H. H., Chem. Revs., 53, 198 (1953); (b) Berliner, E., M. C. Beckett, E. A. Bloomers, and B. Newmm, J. Am. Chem. Soc., 74, 4940 (1952).
I . Ionization, ArCO,H, H,O, 25" 2. Ionization, ArCO,H, 50% aq. EtOH, 25" (R) 3. Ionization, ArCO,H, 50% aq. EtOH, 25" (W) 4. Ionization, ArCO,H, 10%aq. EtOH, 25" 5. Ionization, ArCO,H, 75% aq. EtOH, 25" 6. Ionization, ArCO,H, 80% aq. Me cellosolve, 25" 7. Ion-pair formation, ArC0,H with 1,3-DPG,benzene 25" 8. Rate, saponification, ArC0,Et 60% aq. acetone, 25"
No.
Basis Sets for UR(BA type) Values
TABLE 11
rl
Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization, Ionization,
\
26. Saponification, ArCO,Et, 88% aq. EtOH, 30" 27. Esterification, ArCO,C,,H,,, (-OMe), MeOH, 40"
AI-N-N
N, ethylene glycol,
I//
I
Reaction
ArCO,H, 43.5% dioxane -H,O, 25" ArCO,H, 73.5% dioxane -H,O, 25" ArCO,H, ethylene glycol, 25" ArCO,H, MeOH, 25" ArCO,H, EtOH, 25" ArCO,H, n-PrOH, 25" ArCO,H, n-BuOH, 25" ArSO,NH,, H,O, 20" ArSO,NHC,H,, H,O, 20" ArAs(OH),O; H,O, 22" ArSe(OH),, H,O, 25" A r c s - C O , H , 50% aq. EtOH, 25" A r M - C O , H , 35% aq. dioxane, 25" trans-ArCH=CHCO,H, H,O, 25" cis-ArCH=CHCO,H, 50%aq. EtOH, 25" 2-MeArCO2H, 50% aq. EtOH, 25" H,N-C=N
25. Rearrangement, 194O
9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
No.
2.602 2.578
1.371
1.426 1.525 1.247 1.358 1.535 1SO5 1.486 1.078 1.140 .898 1.068 .694 .721 .450 .810 1.656
Pf)
2.307 2.212
Rates
1.178
1.153 1.241 1.044 1.139 1.182 1.227 1.217 .872 .943 .683 .812 .664 .687 .439 .643 1.594
Equilibria
P%
.89 .86
.86
.8 1 .81 .84 .84 .77 .82 .82 .81 .83 .76 .76 .96 .95 .97 .79 .96
AP
.04 .06 .03 .07
5 7 4 5 4 5 5
11 6
5
.05
5
.06 .02
.03
.05
.02
.05
.02 .02 .02 .03 .02 .03 .01 .03
SD
7 7 8 8 8 7 7 6
n
Benzoic Acid Type Series. Fits to Eq. (1) with Use of UR(BA) Values
TABLE 111
,072 .013
.041
,030 .050 .027 .075 .087 .lo6 .I54 .08 1 .217 .258 .05 8 .059
.050
.040 .04 1 .044
J'
2.593 2.608
1.310
I .453 1.556 1.269 1.382 1.545 1.531 1.514 .997 1.062 .827 .961 .712 .731 .470 .794 1.702
P
Reaction 0
, 15% aq. EtOH,
-2.710 16.811 4.400 -3.315 -5.651
F-nrnr Shifts
1.06 1.81 1.40 1.03 1.32
.94 .45 .89 1.04 -.37 .93 .74
2.925 ,112 -2.302 -2.404 .I94 243 .296
3.107 ,250 -2.576 -2.316 - .527 .902 .403
-2.549 9.297 3.148 -3.225 -4.279
.96
1.10
hP
1.268
1.931
Pa
1.317
1.761
4
.03 .03
9 7 4 8 5
.065 .070
.I 10 .035
.07 .35 .15
.18 .07
.059
.157
.169 .064
.05
6 10 6
5 5
.021 ,274 .055 .030
.03 .03 .06 .03 4 7
.065
f
.076
.06
SD
.04
8
8
n
-2.605 1 1.28 3.892 -3.370 -4.446
3.177 . I 84 -2.61 8 -2.441 - .396 ,912 .327
1.361
1.942
P
9. Elliott, J. H., and M. Kilpatrick, J. Phys. Chem., 45, 485 (1941). 10. (a) Elliott, J. H., and M. Kilpatrick, J. Phys. Chem., 45, 485 (1941); (b) Kilpatrick, M., Chem. Revs.,30, 159 (1942). 11. (a) Elliott, J. H., and M . Kilpatrick,J. Phys. Chem., 45, 472 (1941); (b) Kilpatrick, M., and R. D. Eanes,J. Am. Chem. Soc., 65, 589 (1943); (c) Kilpatrick, M., Chem. Revs., 30, 159 (1942). 12. (a) Elliott, J. H., and M. Kilpatrick, J. Phys. Chem., 45, 454 (1941); (b) References (b) and (c) for set no. 1 1 .
*37. ArCOC,H,F@), CH2C1,, 25" 38. ArCH,F, CCI, 39. ArSF, (apex), CC1, 40. ArC,H,F@), benzene or DMF 41. ArSC,H,F@), CH,C12 ,25"
CH 29. Saponification, trans-ArCH=CHCO,Et, 88% aq. EtOH, 30" 30. Hydrolysis, (ArCO),CO, 75% aq. dioxane, 58" 31. Thermal decomposition, ArCO,Et, 515" 32. Solvolysis, ArSCH,CI, 50% aq. dioxane, 35" 33. Decomposition, ArCONOCOC,H;K+, H,O, 30" 34. Esterification, ArCO,H, (HCl), MeOH, 25" 35. Reaction, ArCO,H, DPDM, EtOH, 30" 36. Reaction, rrans-ArCH=CHCO,H, DPDM, EtOH, 35"
28. Saponification, X25"
No.
TABLE 111 (continued)
W
13. (a) Elliott, J. H., and M. Kilpatrick, J. Phys. Chem., 45, 466 (1941); (b) References (b) and (c) for set no. 1I . 14. (a) Elliott, J. H., J. Phys. Chem., 46, 221 ( I 942); (b) Reference (c) for set no. 11. 15. References (a) and (c) for set no. 1 1 . 16. Willi, A. V., Helv. Chim. Acta, 3 9 , 4 6 (1956). 17. Reference for set no. 16. 18. Pressman, D., and D. H. Brown, J. Am. Chem. SOC., 65, 540 (1943). 19. Gould, E. D., and J. D. McUllough,J. Am. Chem. SOC.,71, 674 (1949); 73, 1109 (1951). 20. Benghist, I., and E. I. Becker,J. Org. Chem., 23, 885 (1958). 21. (a) Newman, M. S., and S. H. Merrill, J. Am. Chem. SOC.,77, 5552 (1955); (b) Soioman, I. J., and R. Filler,J. Am. Chem. SOC.,85, 3492 (1963). 22. Dippy, J. G., and J. E. Page,J. Chem. SOC.,357 (1938). 23. Fuchs, R., and J. J. Bloomfield, J. Org. Chem., 31, 3423 (1966). 24. Roberts, J. D., and J. A. Yancey,J. Am. Chem. SOC., 73, 1012 (1951). 25. Henry, R. A., W. G. Finnegan, and E. Leibler, J. Am. Chem. SOC.,76, 88 (1954). 26. (a) cf. JaffB, H. H., Chem. Revs., 53, 198 (1953); (b) Berliner, E., M. C. Beckett, E. A. Bloomers, and B. Newman, J. Am. Chem. SOC., 74, 4940 (1952). 27. Taft, R. W., M. S. Newman, and F. H. Verhoek,J. A m . Chem. SOC.,72, 451 1 (1950). 28. Tirouflet, J., Bull. Soc. Sci Bretagne Spec., 26,89 (1951); CA, 47,8694 (1953). 29. Kindler, K., Ann., 452, 90 (1927);Ber.. 69B, 2792 (1936). 30. Berliner, E., and H. Altschal,J. A m . Chem. SOC.,74, 41 10 (1952). 31. Smith, G. G., D. A. K. Jones, and D. F. Brown, J. Org.Chem., 28,403 (1963). 32. Bordwell, F. G., G. D. Cooper, and H. Moirta,J. Am. Chem. SOC., 79, 376 (1957). 33. Bright, R. D., and C. R. Hauser,J. A m . Chem. SOC.,61, 618 (1939). 34. (a) Hartman, R. J., and A. M. Borders, J. Am. Chem. SOC.,59, 2107 (1937); (b) Hartman, R. J., and A. B. Gassman,J. Am. Chem. SOC.,62, 1559 (1940). 35. (a) Roberts, J. D., et al., J. Am. Chem. SOC.,73, 2181 (1951); 72, 628 (1956); 71, 2923 (1949); 72, 408 (1950); (b) Benkeser, R. A., ef al., J. Am. Chem. Soc., 78, 682 (1956); (c) Chapman, N. B.,J. Chem. SOC.,1824 (1962). 36. Ritter, J. D. S., and S. I. Miller, J. A m . Chem. SOC.,86, 1507 (1964). 37. Pews, R. G., Y. Tsuno, and R. W. Taft, J. A m . Chem. SOC.,89, 2391 (1967). 38. Bkguin, C., Bull. SOC.Chim.fiance, 4214 (1967). 39. Eaton, D. A,, and W. A. Sheppard, J. Am. Chem. SOC.,85, 1310 (1 963). 40. Dewar, M. J. S., and A. P. Marchand,J. Am. Chem. SOC.,88, 3318 (1966). 41. Unpublished results of R. G. Pews, P. Heffley, and R. W. Taft.
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Values of SD and f=SD/RMS for Para BA Series
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TABLE 1V
IEZ' P60' ZEP' 28 I' 6PI' P I I' 9s I' ILLE9" LE 1LEI' ZSI' ESI'
89 I' ESZ' 69 I' PZZ' 190' ZLI' SE I'
s 10.
e801' PLO' eLZI' eE I I' 6P0 eP80' 9960' eL 10'
0
*
r
c
.I72 .138 .I54 .207 .072
.20 .74 .33 .33 .14
.064 .157
.059 .065 .070 .I10 .035
.07 .35 .I5 .18 .07
37 38 39 40 41
.I69
.030
55 1.56 .73 .56 .29
.144 .146 .245 .239
.474 .290 .339 .329 .143
F-nmr Shifts
.358 .I56 .288 .393 .I72 .384 .230 .241 .204 .292 .257
Other Rates
.32 .I9 .28 .22 .24 .04 .24 .24 .06 .I2 .04
.20 .I5
.05
.03
.15 .69 .32 .25 .17
.05 .05
.05
.05
.lo5 .07 .I 3 .05 .11 .03 .07
.06 .05 .I0 .08
.I21 .I29 .I52 .I53 .086
.157 .056 .I46 .097 .076 .269 .062 .048 .I80 .I21 .289
.274 .I54 .I23 .124
.12 .36 .09 .27 .I3
.06 .04 .01
.09 .05
.I1 .04 .08 .06 .04 .03
.05 .02 .05 .04
.064
.170
.I 24a .066 .043
.120 .037 .088 .111 .031 .296 .081 .047 .202 .099 .058
.221 .066 .056 .061
.I4 2.49 .48 .28 .35
.05
.09 .09 .23 .04
.05
.ll .07 .I2 .06 .05
.05
.05
.05 .05
.I21 .462 .225 .I76 .173
.I 17 .059 .I34 .111 .037 .564 .088 .087 347 .097 .316
.225 .147 .057 .085
*
Datum for NMe, not included, no R value listed. bData for NMe,, SCF, and SOCF, not included, no R values listed. Results including datum for NMe, and corrected datum for NHCOMe, which were not available at time UR(BA) values of Table I were defined. Results including data for NMe,, NHCOMe and CO,R, which were not available at time UR(BA) values of Table I were defined.
a
.195 .069 .I74 .237 .070 .334 .I18 .110 .194 .I77 .080
.17 .08 .I6 .I3 .I0 .03 .I3 .ll .05 .07 .01
.072 .013 .065 .076 .021 .274
.06 .02 .06 .04 .03 .03 .06 .03 .05 .03 .03
26 27 28 29 30 31 32 33 34 35 36
.055
.168 .069 .I10 .I14
.04 .02 .09 .07
.258 .058 .059 .041
.05 .02 .05 .03
22 23 24 25
12
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
Table IV lists comparative SD and f values for fittings of all of the reactions of Table 11 and 111 with each of the UR scales derived in this paper. The comparison includes figures for fittings with F and R valu,es of Swain and Lupton (S & L) and fitting with the Hammett equation. We believe the results given in Table IV provide a clear confirmation of the uniqueness and limited generality of the UR(BA) scale. Very consistently, the fit achieved by the UR (BA) scale is shown in Table IV to be superior by significant factors to that achieved by any of the other scales or by the simple up treatment. This fact is clearly reflected in the overall f values and the similarly weighted root-mean-square f values, F 3 dlCnifiZ/N, sum taken over all reactions. The value of F is .067 for the basis sets of Table I1 (compare with overall f of .058). The comparable F values are .140 for u i , .088 for S & L, and .155 for I?(,,) with the data differences as explained in Table IV. For all sets of Table IV, the corresponding , .097 for S & L, and .209 for a@). figures are .073 for uR(BA), .143 for The OR values of Table I show notable similarities to the previously proposed values. The small differences, of course, result from the influence of the seven other reactions, besides reaction 1, which were used to define the results in Table 1. Three substituents may be singled out as having appreciably modified values: namely, SMe, OC6H5, and NHCOMe. These three substituents give deviations twice as large as for any other substituents in the fitting of reaction 1 and are largely responsible for the substantially greater fvalue for this reaction than for the other seven basis sets. Either experimental errors or specific hydration effects are probably involved with these substituents in reaction 1. For example, the larger -UR value for OC6HS than OCH3 derived from log ( K / K o ) values for reaction 1 is unreasonable (and not observed in any other reaction series). The UR value of -.55 for OC6Hs-defined by the data of reaction 8 is probably a more reasonable value than the -.58 value based upon the data of both reactions 1 and 8. Swain and Lupton neglected without comment the above point regarding the OC6H5 substituent (giving -R for OC6H5 > -R for OMe). Much more serious in its consequences is the fact that Swain and Lupton, again without comment, have neglected the available reliable data for the NMez substituent. Because the NMez substituent is a highly important one with regard to data sets covering a full range of CJR electronic effects, the fittings achieved by neglect of this substituent should be taken less seriously (even though statistically we have attempted to account for the omission in the fvalues through the RMS values). A brief discussion of the systematics of solvent effects on the pi, p~ , and h values of Tables I1 and I11 is presented in the discussion section. However, it is worthy of note here that sets 7, 37, 38, 39, 40, and 41, which involve nonhydroxylic solvents, are fitted with comparable precision to that for reaction series in aqueous or mixed aqueous organic solvents. The present analysis does not support the previous assignment (7b) of ion-pair formation of benzoic acids
I?;
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
13
with 1,3-diphenylguanidine (DPG) in benzene (reaction 7) as a sigma zero type, but instead supports assignment as a BA type (with relatively small Xp = .69) in accord with structural considerations.
B. ur; (A type) Values The ionization of anilinium ion in water at 25" was adopted as the basis set for this type. This choice was dictated by the fact that extensive reliable data for both m- and p-substituents are available which meet the minimal substituent requirement in both series. Two methods were found which give essentially the same set of ur; parameters. First, the UR(BA) parameters for the substituents CH3, F, C1, and Br were assumed to apply to the data for m-and p-substituted anilinium ions. This constraint was sufficient to give a or; set essentially equivalent to the values given in Table V. Second, the data include results for the TABLE V Pi Delocalization Parameters Substituent - -
U B
uR(BA)
OR(A)
-.83 -.82 -.36 -.61 -.58 -.32
-.34 -.48 -.45 -.I4 -.I I .04 -.45 -.23 -.I9 -.I1
Uii
~
-N(CH,)a -NH, -NHCOCH, -OCH, -OC,Hs -SCH, -CH, -C& -F -c1 -Br -I -H -SOCH, -SCF, -Si(CH,), -SF, -SOCF, -CF , -SO,CH, -CN -COaR -NO, -COCH,
(.06)a -.52 (.12) -.48 (.26) -.25 (.27) -.45 (.38) -.34 (.23) -.20 (-.04) -.I1 (.lo) -.11 ( S O ) -.34 (.46) -.23 (.44) -.19 (.39) -.I6
(.OO) (50) (.42) (-.lo) (57) (.64) (.45) (S9) (-56) (.30) (.65) (.28)
.oo .oo
.04 .06 .06 .08 .08 .I2 .I3 .14 .I5 .16
a U I values are given in parentheses. b cf. discussion.
-.11 -.I 1
-.45 -.23 -.19 -.16
.oo .oo .04 .06 .06 .08 .08 .12 .I 3 .14 .I5 .16
.oo
.I4 .14 .20 .17 .38 .33 .34 .46 .4 7
-1.75 -1.61 -.86 -1.02 -.87 b
-.25 -.30 -.57 -.36 -.30 -.25
.oo .oo .04 .06
.06 .08 .08 .12 .I 3 .14 .15
.16
14
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
m-and P - N ( C F ~ )substituent ~ (9). This substituent by the very sensitive F-nmr shift method (10) is found to have OR = .OO 5 .01. Consequently, in the anilinium ion ionization equilibria, it is a useful and presumably valid assumption to take R Z.00 for m- and p-N(CF3)*. This assumption gives log (KP/Ko)/log ( K m l K o ) = P I P = pp/$ = 1.46/1.31 = 1 .I 1. Because p y is obtained as 2.9 . I (this value is essentially independent of the OR scale used in eq. (1): see subsequent discussion of meta reaction types), we have pf = 3.2 k .l. The generation of the u i (A) basis set is then completed (using the p-substituent data only) by the assignment of p$ = 3.50, which gives a 0% value of -.11 for the CH3 substituent. Because both methods give essentially equivalent results, the results given in Table V were adopted. Interestingly, slightly better precision of fit of the u ~ ( A )scale is achieved if the identity of uR(BA) and aEcA)scales is not extended to the I substituent (i.e., for I , o ~ ; ( A )= -.11 and UR(BA) = -.16). For all other substituents, ugcA, and uR(BA) values differ very significantly (Table V) as do the statistics of fitting of data for various reaction types b y use of these two scales (Tables IV, VII, IX, XII, XIV). Table VI lists values of &, pg , Ap, n, SD, andfobtained for twenty-four reaction series and one proton nmr set of the a i type, each of which contain data for sufficient numbers (n) and kinds of para substituents to provide a reasonably critical analysis. Also given in Table VI is the p value obtained with the single substituent parameter a@)., as listed by Ritchie and Sager (2m). It is immediately apparent from the reaction descriptions that the C J ~ ; (scale ~ ) applies to rate and equilibrium ionization of a proton from the functional groups -CH3, - N G , -N(CH3),Ht, -NH2, -SH,-OH, etc. There is, however, the important restriction (as discussed fully subsequently) that the ionization of p-substituted phenols in certain hydroxylic solvents may not be included. In Table VII are shown the comparative SD and f values for fittings of these reactions with the various substituent parameter scales. These results, we believe, provide a dramatic confirmation of the uniqueness and “limited” generality of the scale. In all but three of the twenty-five sets, there is significantly better fitting by eq. (1) with values than by the single substituent parameter treatment, pa@). In contrast, the single substituent parameter treatment gives fits better by significant factors than the Swain treatment (in spite of the additional substituent parameter in the latter) in 50% of the sets of Table VII. In only four cases does the Swain treatment give better fit than P O ( , ) by significant factors, and in three of these the absence of an R value for the NMe, substituent precludes complete coverage of the data by the Swain parameters. The F value is .194 for pa@, and .212 for the R and F treatment. In n o case does the Swain treatment give better fit than eq. (1) with ~ j i ( ~values ) (F = .080). In fact, in many sets, the SD and fvalues in the Swain treatment (also with UR(BA) and a;) are so large that the fittings are meaningless. In spite of this poor quality of fit, the applicability of the R and f +_
VI
c
20.
19.
18.
8. 9. 10. *11. 12. 13. 14. 15. 16. 17.
1. 2. 3. 4. 5. 6. 7.
No.
Aminolysis, ArNH, with HCO,H, aq. pyridine 100" Substitution, ArNH, with 2,4-diNO,C6H,Cl, EtOH, 100" T-H Exchange, ArCH, + RNHLi
4.502
-2.516
-2.624 3.764
-1.862
Rates
6.545 3.439 1.958 2.1 10 2.407 2.494 5.084 5.875 4.989 12.159
3.476 3.486 3.890 4.5 94 3.962 4.075 4.5 38
P%
-1.562
5.697 3.485 1.816 2.628 2.971 3.187 5.499 6.575 5.085 9.306
3.088 3.204 4.198 4.708 3.944 3.753 4.506
Ionization, ArNH:, H,O, 25" Ionization, ArNH:, 50% aq. EtOH, 25" Ionization, ArNH:, MeOH, 25" Ionization, ArNHi, EtOH, 25" Ionization, ArNMe,H+, H,O, 20" Ionization, ArNMe,H+, H,O, 25" Ionization, ArNMe,H*, 45% dioxane -H,O, 25" Ionization, ArNH,, NH,(l) Ionization, ArNH,C,H:, 20% aq. EtOH Ionization, ArNHSO,C,H,, H,O, 20" Ionization, ArSH, 48% aq. EtOH, 25" Ionization, ArSH, 95% aq. EtOH, 22" Ionization, ArOH, 95% aq. EtOH, 22" Ionization, ArOH, acetone Ionization, 2,6-diMe phenol, acetone Ionization, ArNHC,H,, DMSO, 25" Oxidation, [Ar(C,H,)C,H,F@)] -,DMSO, 25"
Equilibria
P4
Reaction
1.20
.96
1.19
1.15 .99 1.08 .80 .81 .78 .92 .89 .98 1.31
1.13 1.09 .93 .98 1.oo 1.09 1.01
xp
.14
7
.08 .07
4
.04 6
5
5
6 10 7 8 10 7 6
5
.12 .06 .03 .08 .10 .10 .28 .36 .7 1 .44
.10
5
4
.03 .03 .04 .09 .14
SD
18 6 4 4 6
n
Anilinium Ion Type Series. Fits t o Eq. (1) with Use of C T ~ ( AValues )
TABLE VI
'
,056
.084
.049
.043 .026 .030 .058 .069 .063 .093 .092 .217 .078
.018 .015 .034 .072 .039 .05 8
.015
f
3.1 11
-2.208
-1.50,3
5.835 3.127 1.576 1.966 2.428 2.581 4.870 5.700 4.313 7.953
2.862 3.006 3.673 4.195 2.864 3.593 3.917
P
m
-
H,)C, H, %)I-,
DMSO,25" -10.37
-13.11
.776
6.436
6.103
5.031
-22.80
' nmr Shifts
1.579
-12.80
F-nmr Shifts
N'
1.45 3
pg
.879
H-nmr Shift _____
.932
5.572
5.648
5.855
,499
PP
1.23
1.74
1.09
.83
1.16
1.08
.86
1.76
kP
7
7
15
6
6
6
12
5
n
.36
.71
.I1
.01
.25
.19
.I5
.03
SD
.063
.090
.I33
.030
.072
.065
.054
.077
f
-8.54
-15.04
1.280
.752
5.322
4.905
4.792
.605
P
1. (a) Bigs, A. I., and R. A. Robinson, J. Chem. SOC.,388 (1961); (b) Bordwell, F. G., and P. J. Boutan,J. Am. Chem. Soc., 78, 87, 854 (1956); 79, 717 (1957); (c) Bordwell, F.G., and G. D. Cooper, J. Am. Chem. SOC., 74, 1058 (1952); (d) Benkeser, R . A . , and H. R. Krysick, J. Am. Chem. SOC., 75, 2421 (1953); (e) Vandenbelt, J., C. Henrick, and S. Vandenberg, Anal. Chem., 25, 726 (1954); ( f ) Robinson, R. A., and A. 1. Biggs, Aust. J. Chem., 10. 128 (1957); (g) Willi, A. V., and W. Meier,HeZv. Chim. Act., 39, 318 (1956); (h) Fickling, M. M., A. Fischer, B. R. Mann, J. Packer, and J. Vaughan, J. Am. Chem. Soc., 81, 4226 (1959); (i) Fawcett, F. S., and W. A. Sheppard, J. Am. Chem. SOC.,87, 4341 (1955); 0 ) Sheppard, W. A., J. Am. Chem. SOC.,84, 3072 (1962); 85, 1314 (1963); (k) Kuhn, R., and A. Wassermann,HeZv. Chim. Act., 11, 3 (1928); (I) Kieffer, F., and P. Rumpf, Compt. Rend., 238, 360 (1954); (m) Sager, E. E., e l aZ., J. Rex NatZ. Bur. Stand., 35, 521 (1945).
28.
[ ArC(C,
ArNH, , DMSO, 25"
a
27.
25.
24.
23.
ArOH, DMSO, 25"
ArOH + H,SO,,
*26.
-.+
Substitution, C1- Q -X with SC,H;, MeOH, 35" NO* Substitution, F-X with OC,H;, EtOH, 49.6" Cleavage of ArCH,SiMe,, OH-, 39% aq. MeOH, 49.7" Deprotonation, ArCH(NO,)CH, with O H - , H,O, 25"
NO*
Hydrolysis, ArOS0,H H,O, 49"
Reaction
*22.
21.
No.
TABLE VI (continued)
c. 4
2. Baddeley, G., J. Chadwick, and H. T. Taylor,J. Chem. SOC.,2405 (1954). 3. Kilpatrick, M., and C. A. Arenberg, J. Am. Chem. Soc., 75, 3812 (1953). 4. Reference for set no. 3. 5. Willi, A. V.,Helv. Chim. Act., 40, 2019 (1957). 6. Fickling, M. M., A. Fischer, B. R. Mann, J. Packer, and J. Vaughan,J. Am. Chem. Soc., 81, 4226 (1959). 7. Sheppard, W. A., J. Am. Chem. Soc., 87, 2410 (1965). 8. Birchall, T., and W. L. Jolly, J. Am. Chem. Soc., 88, 5439 (1966). 9. Dolman, D., and R. Stewart, Can. J. Chem., 45,903 (1967). 10. Willi, A. V., Helv. Chim. Act., 3 9 , 4 6 (1956). 11. (a) Schwarzenbach, G., and H. A. Egli, Helv. Chim. A c t , 17, 1176 (1934); (b) Schwarzenbach, G., and E. Rudin,Helv. Chim. Act., 22, 360 (1939); (c) Bordwell, F. G., and H. M. Andersen, J. Am. Chem. Soc., 75, 6019 (1953); (d) Bordwell, F. G., and P. J. Boutan,J. Am. Chem. SOC.,78, 856 (1956). 12. Reference (b) for set no. 10. 13. (a) Schwarzenbach, G., and H.Egli,Helv. Chim. Act., 17, 1 176, 1183 (1934); (b) Reference (b) for set no. 10. 14. Fischer, A., G. J. Leary, R. D. Topsom, and J. Vaughan,J. Chem. Soc., (B), 846 (1967). 15. Reference for set no. 13. 16. Dolman, D., and R. Stewart, Can. J. Chem., 45, 9 I I ( I 967). 17. McKeever, L. D., and R. W. Taft, J. Am. Chem. SOC.,88, 4544 (1966). 18. Davis, 0. C. M., and F. W. Rixon,J. Chem. SOC.,107, 728 (1915). 19. Van Opstall, H. J.,Rec. Dm.Chim., 52, 901 (1933). 20. Streitwieser, A., Jr., and H. F. Koch, J. Am. Chem. Soc., 86, 404 (1964). 21. Burkhardt, G. N., C. Horeux, and D. I. Jenkins,J. Chem. Soc., 1649 (1936). 22. Porto, A. M., L. Altieri, A. J. Castro, and J. A. Brieax,J. Chem. Soc., (B), 963 (1966). 23. Bevan, J.,Bull. Chim. SOC.Fr.,1551 (1959). 24. Eaborn, C., and S. H. Parker, J. Chem. SOC., 126 (1955); Bott, R. W., C. Eaborn, and B. M. Rushton,J. Orgunometallic Chem., 3, 448 (1965). 25. Bordwell, F. G., and W. J. Boyle, Jr.,J. Am. Chern. Soc., in press. 26. Tribble, M. T., and J. G. Traynham,J. Am. Chem. SOC.,91, 379 (1969). 27. Axenrod, T., P. S. Pregosin, M. J. Wieder, E. D. Becker, R. D. Bradley, and G. W. A. Milne, J. Am Chem. Soc., 93,6536 (1971). 28. Dayal, S. K., S. Ehrenson, and R. W. Taft, J. Am. Chem. SOC.,94,9113 (1972).
m
c
.lo
9.
8.
11.
12.
.I4 .12 .06 .03 .OX .10
6. 7.
5.
.015 .018
.03 .03 .04 .09 .I4
1.c 2. 3. 4.
.043 .026 .030 .058 .069
.058
.015 .034 .072 .039
f
OR(A)
SD
10.
No.
.40 .38 .17 .34 .28 .36 .25
.75
.44 .16 .18 .30
SD
f
.060 .144 .252 .251 .167
.155
.380 .I57
.111
.078
.I00
.244
OR(BA)
.I8
.15 .26
.58 .30 .29 .34 .23
.31 .16 .22 .27
SD
4
.123 .097 .141 .184 .122
.117
.092 .lo0 .293 .117
.lo0
.I74
f' .28 .38 .49 .88 .47 .47 .53 .42 .35 .44 .32
.60
SD
4 .323 .172 .I64 .183 .446 .186 .I93 .193 .I78 .319 .310 .218
f'
SD/RMS for Para A Series
TABLE VII
Values of SD andf
.18 .I6
.44 .34 .38 .29 .30 .25
.42 .22 .24 .36
SD
f
.128 .231 .123b .lo7
.lo5
.239a .I38 .lo2 .I33 .210b .135 .I59
S&L
.24 .I I .I 3 .09 .74 .09 .21 .29 .13 .I4 .42 .30
SD
f
.033 .375 .036 .086 .106 .056 .128 ,293 .202
.056
.i33 .107
06)
.71 .36
.ll
.10 .28 .36 .71 .44 .04 .08 .07 .03 .15 .19 .25 .01
.063 .093 .092 .217 .078 .049 .084 .056 .077 .054 .065 .072 .030 .133 .070 .063
.32 .52 .70 .96 2.12 .17 .43 .24 .09 .65 1.03 .60 .07 .19 2.74 1.97
.I98 .173 .178 .294 .373 .195 ,463 .191 .215 .228 .349 .174 .143 .240 .335 .344 .62 .60 .06 .15 2.02 1.50
.51
.24 .46 .62 .81 1.70 .ll .48 .22 .07
I
a Data for SCF, and SF, not included, no R value listed. Datum for NMe, not included, no R value listed. Basis set
13. 14. 15. 16. 17. 18. 19. 20. 21. *22. 23. 24. 25. 26. 27. '28.
.150 .151 .158 .249 .299 .123 .513 .I77 .163 .I79 .210 .I74 .121 .186 .254 .262 .43 .12 .88 1.32 .87 .10 .26 3.55 2.60
.54
.40 .77 .97 1.08 2.85 .22
.250 .256 .247 .329 SO2 .252 .579 .342 .280 .308 .444 .253 .214 .322 .446 .456 .06 .19 2.43 1.26
.55
.96 .9 8 .16 .31 .I 8 .07 .62 1.oo
.55
.22 .44 .139 .146 .139 .294 .1 60b .175 .329 .143 .155 .216 .337 .160 .I19 .234b .306 .213b
.32 .40 .46 .84 1.68 .04 .23 .19 .07 .65 56 .34 .06 .19 2.38 1.44
.loo
.135 .239 .299 .252
.199 ,133 .117 .256 .296 ,048 .247 .152 .170 .226 .190
20
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
parameters to reactions such as those of Table VI was clearly implied by Swain. The explanation lies in the fact that not a single reaction from Table V1 was considered, nor was any consideration given t o the omission. Swain included the ionization of phenols in water at 25" as the only 06, example, and we have found (as noted above and discussed subsequently) this single set to be notably exceptional. In Table V, the u i ( * ) value given for the p-NMe2 substituent is a secondary value derived from the fittings from among the other reactions of Table VI. The neglect of the NMe, substituent in Swain's treatment was critical in view of the large and variable UR values for this substituent shown in Table V.
C. ;a Values Series for which neither tR nor -R substituent effects from the para position are enhanced or retarded by quinoidal resonance effects have been proposed (2e, 7b) as constituting a unique class. Reactions in which a methylene group is interposed between the side-chain reaction center and the benzene ring were considered especially appropriate for this sigma zero (SO) class (7b). However, data of this type were meager, and substituents effects in such reaction series are relatively small compared to small specific solvent effects or to experimental errors. The F-nmr shielding effects of p-substituents in fluorobenzenes clearly do not suffer from the latter disadvantage, and these substituent effects appeared to be well correlated by ;0 values obtained from the available reaction series data (7b). Consequently, the F-nmr shifts were given a strong weighting in defining the originally proposed ug scale. A number of apparently appropriate reaction series data have become available in recent years. Using essentially the above structural considerations, we have found 14 reaction series which we believe are appropriate for the SO classification. These reactions are listed in Table VIII. Unfortunately, only reaction 1 meets the minimal substituent requirements for a basis set. The other reactions contain sufficient numbers and kinds of substituents to be considered only partially adequate. In view of this shortcoming and the problems which arise from the relatively small R effect contribution to sigma zero substituent effects, the following procedure was adopted. The F-nmr shielding effects for three sets were added to the fourteen sets of reaction data: the p-FC6H4X, cyclohexane; p-FC6H4X, methanol; p-FC6H40C6H4X,benzene. It should be noted here that the units of the F-nmr shifts compared to the log (k/k,) values are such that sets 15, 16 and 17 are very highly weighted in the determination of the u$ scale. In the statistical sense, this weighting is justified by the relatively high precision of the F-nmr shifts. In the physical sense, however, it is not clear that the high weighting is justified. Although F is the weakest pi electron donor of the united-atom-like first-row pair donor
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
21
substituents, it has a definitely finite UR value in any of the scales of Table V. Consequently, enhanced or retarded effects on the F-nmr shifts associated with para quinoidal type pi delocalization of the fluorine atom probe may be expected to contribute to some extent (1 1). In the absence of data which are truly ideal in the physical sense, the fluorobenzene and fluorodiphenyl ether shifts have been utilized as described below. The comparable precision of fit found upon putting the F-nmr shifts and reactivity sets together in the generating of the u i scale provides some support for this procedure. The u i values presented in Table V were obtained from best fitting the seventeen adopted basis sets as follows: first, the 01 values of Table I and the UR(BA) values of TableV for NOz, C1, Br, and I were used. For these substituents, values and the original u i values did not differ significafitly. The set of u$ values so generated was compared with the u R ( ~ and ~ ) ui(A) sets. If differences of a few hundredths of a unit existed, it was assumed and subsequently verified that adjustment to a common value could be accommodated with no significant loss of precision of fitting. In this manner, for example, the values of uR(BA) and ;u for all +R substituents could be set equal. The first generated ug value for the CH3 substituent was -.16. However, this value is considered to be an artifact of the F-nmr shielding data for p-FC6H4X. All of the data for this substituent is satisfactorily fitted by the value of -.I1 given in Table V. Table VIII lists values of p f , p g , hp, n, SD,f; and Hamrnett p obtained for the seventeen sigma zero type basis sets with the u i values of Table V. Also listed are these results for 10 additional data sets. The comparative values of SD and f obtained with the various substituent parameters are given in Table IX. At first glance, it appears that the 14 basis set reaction series do not discriminate nearly as well between the various scales of OR as did the data of the previous sections. Seven of the fourteen sets are best fitted by a$ ; four sets are best fitted by Swain and Lupton parameters; two sets are best fitted by u ~ ( A ) parameters, and one set best fitted by UR(BA). A more complete examination reveals that in only three of the reactions (nos. 2, 9 , 13) not best fitted by the ug scale is the fitting by the competing scale better by a significant factor of two to three. Further, for all 14 sets, fits with cr; fall within the range o f f values of .022 to .126, with an overall value of .096. (The root-mean-square value, F, is .091.) Other parameters give overall fits which are notably poorer. For example, the root-mean-square F values for all 27 sets of Table VIII are us, .095;0R(,A), .159;S & L, . 1 8 8 ; ~ j j ( ~ .251;and ), u;, .257. The three F-nmr shielding sets (nos. 15, 16, 17) are fitted with uniquely better precision by the u i scale. The SD for each of these sets is smaller by factors of two to three times than that achieved with any other parameters (Table VIII). This result is consistent with the fact that these sets have much larger h values (1.5 t o 4.2) than do the reaction series (.7 to 1.0) and
2
*15. *16. 17.
F-nmr Shift, ArF, MeOH, 25" F-nmr Shift, ArF, cyclohexane, 25" F-nmr Shift, ArOC,H,F(,), benzene, 25"
Saponification, ArCH,O,CMe, 60% aq. acetone, 25" Saponification, ArCH,CO,Et, 60% aq. acetone, 25" Saponification, ArCH,CO,Et, 88%aq. EtOH, 30" Saponification, ArCH,CO,Et, 60% aq. acetone, 25" Saponification, Ar(CH,),CO,Et, 88% aq. EtOH, 30" Saponification, I-Ar-cyclopropyl CO,Et, aq. Decomposition, (ArO),CO(,), 363"
8. 9. 10 11. 12. 13. 14.
6. 7.
5.
Ionization, ArCH,CO,H, 50% aq. EtOH, 25" Ionization, ArCH,CO,H, 10% aq. EtOH. 25' Ionization, ArCH,CO,H, H,O, 25" Ionization, ArCH,NH:, 50% aq. EtOH, 25" Ionization, ArCH,NH:, H 2 0 , 25" Ionization, ArPO,(OH)-, H,O, 25" Ionization, f-Arcyclopropyl CO,H, 50% aq. EtOH, 25"
Reaction
*l. 2. 3. 4.
No.
-9.021 -7.033 -3.210
F-nmr Shifts
.7 14 1.066 1.173 1.044 .641 .857 ,182
Rates
.755 .556 ,484 1.282 1.082 1.082 S72
Equilibria
A. Basis sets
-31.17 -30.58 -4.854
.775 .159
.520
.718 .795 .790 .869
.646 .470 ,433 1.269 1.057 1.142 .501
BR
3.46 4.35 1.51
1.01 .75 .67 .83 .81 .90 .87
.86 .85 .90 .99 .98 1.06 .88
hP
Sigma Zero Sets. Fits to Eq. (1) with Use of &Values
TABLE VIII
5
22
21
7
5
8 7
5
8 7
11 9 7 8 8 7 5
n
.56 .56 .05
.03 .04 -05 .02 .02 .02 .01
.02 .02 .01 .05 .05 .04 <.01
SD
.072 .076 ,027
.086 .095 ,121 .063 .lo4 ,049 ,126
.060 ,087 .067 ,114 .119 ,099 .022
f
-14.99 -1 3.30 - 3.446
,732 ,985 .813 .981 .404 .835 .142
.562 .555 .481 1.097 .908 .937 ,553
P
E
Methanolysis 4-X, 2,6-diNOZchlorobenzene, MeOin MeOH, 0" Piperidine with 4-X, 2-NO, chlorobenzene, benzene, 45" Acetolysis. 6-X-syn-9-Arnorbornenol brosylates, HOAc, 77.6"
-1.851
5.369
5.96 1
-1.530
7.069
8.242
.83
1.32
1.38
4
11
7
.03
.25
.19
-1.73
5.436
.loo .033
5.545
.094
1. Wepster, B. M., private communication. 2. Reference for set no. 1. 3. (a) Dippy, F. J., el al., J. Chem. Soc., 161, 1888 (1934); 343 (1935); 644 (1936); 355, 1774 (1937); (b) Fischer, A., B. R. Mann, and J. Vaughan,J. Chern. Soc.,1093 (1961). 4. Reference for set no. I . 5. Reference for set no. 1. 6. Jaffb, H. H., et al., J. Am. Chem. SOC.,75, 2209 (1953). 7. Fuchs, R., C. A. Kaplan, J. J. Bloomfield, and L. F. Hatch, J. Org. Chem., 27, 733 (1962). 8. Tommila, E . , A n n Acad. Sci. Fennicue, 59A, 3 (1942). 9. Norman, R. 0. C., et al., J. Chem. SOC.,3247 (1961). 10. Kindler, K.,Ann., 452, 90 (1927). 1I . Yukawa, Y., Y. Tsuno, and M. Sawada,Bull. Chem. SOC.Japan, 39,2274 (1966). 12. Fuchs, R., and J. J. Bloomfield,J. Org. Chem., 28, 910 (1963); Fuchs, R., and J. A. Caputo,J. Org. Chem., 31, 1524 (1966). 13. Fuchs, R., and J. J. Bloomfield,J. Am. Chem. Soc., 81, 3158 (1959);J. Org. Chem., 28,910 (1963). 14. Smith, G. G., D. A. K. Jones, and R. Taylor,J. Org. Chem., 28, 3547 (1963). 15. Taft, R. W.,etal., J. Am. Chem. Soc., 85, 3146 (1963). 16. Reference for set no. 15. 17. Unpublished data of R. G. Pews and R. W. Taft. 18. Miller, J.,Aust. J. Chem., 9, 61 (1956). 19. Greizerstein, W., R. A. Bonelli, and J. A. Brieux, J. Am. Chem. Soc., 84, 1030 (1962). 20. Tanida, H., Y. Hata, S. Ikegami, and H. Ishitoba, J. Am. Chem. Soc., 89, 2928 (1967).
20.
*19.
18.
Rates
B. Other sets
N
-9.035 -1.676 -1.31 I -5.47 -1.33
nmr Shifts
4.2 10.1
pfl
-29.45 -1.537 -1.175 -21.19 -21.20
-133.2 -170.4
ir Intensities -~
4
3.26 .92 .90 3.87 15.9
-31.7 -16.8
hP
6
7 7 6 11
20 9
n
.6 .9
.29 .07 .03
4.7 4.6
SD
.044 .I06 .079 ,096 ,133
.140 ,128
f
-13.00 -1.426 -.goo -10.89 -9.66
-41.76 -38.10
P
Ray, G. J., R. J. Kurland, and A. K. Colter, Tetrahedron, 27, 735 (1971).
Brownlee, R. T. C., A. R. Katritzky, and R. D. Topsom,J. Am. Chem. SOC.,87, 3261 (1965). Katritzky, A. R.,R. F. Pinzelli, M.V. Sinnott, and R. D. Topsom,J. Am. Chem. SOC.,in press. Illuminati, G., R. W. Taft, unpublished data. Dayal, S., S. Ehrenson, and R. W. Taft,J. Am. Chem. Soc., 94,9113 (1972). Reference for set no. 24. (a) Maciel, G. E., and J. J. Natherstad,J. Chem. Phys., 42, 2427 (1965); (b) Khami, K. S., and J. B. Stothers, Can. J. Chem., 45, 233
F-nmr Shift, 4-X, 3,5-diMefluorobenzene, cyclohexane F-nmr shift, 4'-X, 4-F diphenylmethanols, CH, C1, F-nmr Shift, 4'-X 4-F diphenylmethanes, CH,CI, C-13 nmr Shift, XC,H, (para position) C-13 nmr Shift, Ar,COH (para position), THF.
23. *24. 25. *26. 27.
21. 22. 23. 24. 25. 26. (1967). 27.
(A-100)'/2 1600 cm-' band, X-C,H, (A-80)'/*, 1640 cm-' band, XCH=CH,
Reaction
*21. 22.
No.
B. Other sets
TABLE VIII (continued)
VI
h)
a
.02 .02 .02 .o 1 .56 .62 .05 .19 .25 .03 4.7 4.6 .29 .05 .03 .58 .9
.05
<.01 .03 .04
.04
.02 .02 .01 .05 .05
SD
0 i
f
.033 .140 .128 .044 .072 .017 .096 .133
.loo
.060 ,087 .067 .114 .I19 .099 .022 .086 .095 .121 .063 ,104 .049 .I26 .072 .083 .027 .094 .04 .02 .03 .04 .03 .04 .04 .01 .01 1.49 1.29 .15 .35 .36 .04 7.7 8.6 1.60 .07 .06 .81 1 .o
.08
.04 .03 .02 .05
SD
OR
f
.115 .203 .lo5 .084 .lo2 ,096 .075 .096 ,165 .035 .153 .193 .174 ,081 .176 .146 .048 .228 .235 .243 .091 .146 .134 .138
.131 .125 .lo5
(BA)
.05 .01 .01 .09 .04 .10 .02 .04 .05 .08 .04 .04 .05 .01 2.83 3.00 .30 51 .35 .08 12.4 9.2 1.52 .19 .08 2.61 332
SD
0R(A)
datum for NMe, not included, no R value listed. data for NMe, and SF, not included, no R values listed.
*l. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. *15. *16. 17. 18. *19. 20. '21. 22. 23. * 24. 25. *26. 27.
No.
TABLE IX
f SD
f SD
~~
~
.220 .04 .226 .02 .173 .01 .222 .06 .303 .08 .170 .06 .123 .01 .118 .02 ,158 .02 .05 .122 .170 .02 .262 .03 .076 .01 .250 .01 .323 2.03 .289 1.98 ,144 .19 .291 .35 .227 .34 .089 .02 .348 10.2 .347 10.1 .366 1.23 .208 .05 ,268 .01 .262 .86 .211 .7
S&L
f .152a .082 .079 .134 .201 ,140 ,052 .079 .041 .lo2 .044 .123a .020 .179 .282b .285' .I02 .179 .137 .031 .315d .279 .187 .063a .030a .169a .127a
.ll .05 .04 .13 .13 .09 .04 .04 .I2 .20 .09 .ll .05 .02 3.99 4.30 .19 .39 .34 .16 29.3 35.8 4.3 .21 .16 3.19 5.10
SD
f .395 .226 .234 .289 .339 .211 .179 .134 ,295 .452 .242 .468 .151 ,380 .502 .557 .102 .196 .139 .200 .824 .938 .649 .287 .375 .529 .731
data for NMe,, SCF,, SF, and SOCF, not included, no R value listed. data for NMe,, SF, and SCF, not included, no R values listed.
.181 .06 .031 .05 .072 .03 .199 .10 .093 .12 ,217 .07 .090 .03 .149 .03 ,112 .06 .177 .05 .116 .06 .188 .06 .146 .03 .186 .02 .355 2.53 .395 2.18 ,163 .27 .259 .57 .141 .56 .097 .07 .379 11.7 .252 12.4 .231 2.41 .15 .252 .196 .ll .433 1.58 .455 1.5
0;
Values of SD and f for 0; Sets
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
26
consequently are much more discriminating between the resonance effect scales. However, for the reasons noted above, further evidence for the uniqueness of the u$ scale (in reaction rates and equilibria, in particular) is desirable. Accordingly, additional reactivities and physical property sets have been sought and analyzed to provide more critical evidence in support of the uniqueness of the u$ on a "limited generality" basis. The reactivity sets include the acetolysis of 6-substituted anti- and syn-9-benzonorbornenol brosylates (1 2), and six basis sets from substituent effects in the naphthalene series (2p). The physical property sets include the integrated intensities of the skeletal stretching vibrations of substituted benzenes and ethylenes, the Cl3-nmr shifts at the para carbon position of substituted benzenes and the F-nmr shielding effects of 4'-substituted 4-fluorodiphenylmethanols and 4'-substituted 4-fluorodiphenylme thanes. In the brosylate acetolysis sets, conjugative stabilization of the transition state is geometrically excluded in the syn form, but is anticipated in the anti form (13). That is, on structural grounds, u i is expected to be the parameter of choice for the syn set and u& for the anti set. The available data (for the OMe, Me, C1 and NO2 substituents) do indeed conform to this expectation: 6-Subst.-Syn-9-Ar Norbornenol Brosylate Set (RMS = .77)
4
SD
f
-
.03 .033
OR (RA)
.04
.048
o i -
.07
.089
S&L .02 .031
07@) -
.16 .200
6-Subst.-Aizti-9-Ar Norbornenol Brosylate Set (RMS = 1.34) SD
f
4 -
.06 .045
u~ (BA)
.11 .130
4 -
.28 .208
S&L -
.14 .lo4
"ip,
__
.Ol .05 1
The previous analysis by the dual substituent parameter equation of substituent effects in the naphthalene series provided support for the ug scale, especially for sets involving nonconjugating positions (2p). The available data yield six basis sets which presumably give a critical analysis and, in particular, provide distinctions between conjugative (three sets) and iionconjugative positions (three sets). The results (using the earlier symbolism (2p)) are given in Table X. We regard these results as generally supportive of the expectation that the nonconjugative positions are best fitted by the 0; scale, while the conjugative positions are best fitted by the uK(BA) scale. The few apparent ambiguities which seem to blur this distinction involve sets of relatively low A and RMS values. Katritzky, Topsom, and co-workers (14) have reported correlation of the integrated intensities of the 1600 cm-' benzene skeletal vibration of substituted
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
27
TABLE X Analysis of Naphthalene Series Basis Sets Non-conjugating positions *A.4p. Ionization 4-Substituted-2-Naphthoic Acids (RMS = .505)
SD
f
43 -
O~(A)
OR(BA)
01; -
S&L
32
.04 ,077
.04 .076
.07 .147
.09 .186
.09 .182
.24 .484
*A.7p. Ionization 7-Substituted-2-Naphthoic Acids (RMS = .313, except S & L, .323)
SD
f
.04 ,111
.06 .205
.03 .082
.04 .140
.03 .077
.16 .5 18
*F.6a.Ionization 6-Substituted Quinolinium Ions (RMS = .994, except S & L, 1.052)
SD
f
.06 ,058
.16 .156
.08 .084
.17 .173
.10 .099
.44 .445
Conjugating positions *A.6p. Ionization 6-Substituted-2-Naphthoic Acids (RMS = .361, except S & L, .349) O~(BA)
SD
f
.02 .058
4
.04 .lo5
OR(A)
.10 .285
4
S&L
.06 .172
.02 .063
-
u(P) -
.09 ,251
*C.6p. Rate of Saponification 6-Substituted Methyl-2-Naphthoates (RMS = .832, except S & L, .813)
SD
f
.06 .075
.06 .077
.23 .271
.16 .196
.04 .044
.19 .226
*F.7a. Ionization 7-Substituted Quinolinium Ions (RMS = 1.465)
SD
f
.05 .036
.24 .162
.42 ,289
.12 .082
.06 .042
.28 .193
benzenes and of the 1640cm-' mode of substituted ethylenes with the u i parameter (no u1 dependence). The fittings obtained with this ir data are listed as sets 21 and 22 in Tables VIlI and IX. The fitting achieved by the CJ; scale for both ir data sets is approximately a factor of two better than that obtained for any other parameters. While the fitting with u i is slightly outside of thef'Q .I0 criterion, it seems probable that
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
28
this is associated with the relatively large uncertainties in the data for the weakly interacting substituents. The fittings support Katritzky's conclusions that the U I ~ Iterm is negligibly small ( A = -31.7 for the benzenes; -16.8 for the ethylenes: i.e., -X + -). The notion was also tested that the ir data for benzenes should be used to generate u i parameters which would be more suitable to 14 reactions of Table VIII than the values obtained from the 17 basis sets (Table V). Such a procedure, however, was found to give poorer fits than that achieved by the Table V parameter set. This result suggests again the incursion of the experimental difficulties in the ir data noted above. It is clear, however, that the independent test provided by the ir results does offer further support for a unique u i scale. The C13 shifts at the para carbon position for substituted benzenes (and for fris-p-substituted triphenylmethanols) also support the u i scale as shown by the fitting results of sets 26 (and 27). Set 23 of Tables VIII and 1X gives the fitting results for the F-nmr shifts of 4-substituted-3,5-dimethylfluorobenzenes.Because steric twisting is clearly anticipated for some substituents, e.g., NO2, SMe, and NMe2, only the effects of small or symmetric substituents are considered in the set (specifically, F, Cl, Br, I, Me, CN and NH2). The data of this set are best fitted by ug values by factors in the f parameter of from four to eight. Finally, the fittings achieved with the and methanes (sets 24 F-nmr shifts for 4'-substituted-4-fluorodiphenylmethanols and 25), which involve the p-fluorophenyl tag substituted at fully saturated carbon, also provide critical evidence supporting the ug scale. It may be noted that the results for all available F-nmr shifts of p-fluorophenyl tagged systems are best fitted in accord with the following structural expectations (as presented and discussed in detail subsequently): ug type : diphenylmethanes, diphenyl carbinols, diphenyl ethers UR(BA)
type: benzophenones, biphenyls, diphenylsulfides
u; type: benzophenone adducts of H', BF3, BC13 and BBr3, tripheny!methyl cations. u i type: triphenylmethyl anions
D. rn-Substituent Effects According to earlier considerations, the effects of m-substituents have been considered generally to be of the sigma zero type. Swain and Lupton have questioned this conclusion. We have proceeded in the following manner to obtain evidence on the issue. From all the known data, 1 1 sets of meta substituent reaction series data were found which meet the minimum substituent criterion for basis sets. These reactions are listed in Table XI, with the p y ,p g ,
M
Equilibria
2. cf. Lit. references for Table 11, set 3.
1. cf. Lit. references for Table 11, set 1.
Rate, saponification, ArCO,Et, 60% aq. acetone, 25"
2.367
Rates
.992 Ionization, ArCO,H, H,O, 25" Ionization, ArCO,H, 50% aq. EtOH, 25" 1.454 1.688 Ionization, ArCO,H, 75% aq. EtOH, 25" 1.658 Ionization, ArCO,H, 80%aq. Me cellosolve, 25" 2.360 Ionization, ArOH, H,O, 25" Ionization, ArSH, 48% aq. EtOH, 25" 2.739 2.966 Ionization, ArNHi, H,O, 25" Ionization, 3-X Pyridinium ions, H,O, 25" 6.041 Ionization, 4-X-ZNaphthoicacids, 5O%aq. EtOH, 25" 1.255 Ion-pair formation, ArC0,H-DPG, benzene, 25" 2.175
Reaction
1.129
.403 .620 .726 .827 .440 .839 1.026 2.626 .732 1.031
4
'
.48
.19 .31 .35 .43 .5 8 .47
SO
.4 1 .43 .43
am
Meta Basis Set Reactions. Fits to Eq. (1) with Use of ukValues
14
20 14 14 11 20 9 18 14 8 10
n
.07
.03 .06 .06 .06 .09 .07 .10 .16 .04 .06
SD
.077
.093 .111 .097 .087 ,101 .067 .084 .076 .077 .073
f
2.359
.998 1.413 1.643 1.708 2.307 2.665 2.989 5.936 1.238 2.166
P
3. cf. Lit. references for Table 11, set 5 . 4. cf. Lit. references for Table 11, set 6. 5. (a) Biggs, A. I., and R. A. Robinson, J. Chem. Soc., 388 (1 961); (b) Bordwell, F. G., and G. D. Cooper, J. Am. Chem. Soc., 74, 1058 (1952); Bordwell, F. G., and P. J. Boutan, J. Am. Chem. Soc., 78, 87, 854 (1956); 79, 717 (1957); (c) Kieffer, F., and P. Rumpf, Compt. Rend., 238, 360 (1954); (d) Sager, E. E., et aZ., J. Res. Natl. Bur. Stand., 35, 521 (1945); (e) Kuhn, R., and A. Wasserman, Helv. Chim. Act., 11, 3 (1928); (f) Benkeser, R. A., and H. R. Krysiak, J. Am. Chem. Soc., 75, 2421 (1953); (g) Fickling, M. M., A. Fischer, B. R. Mann, J. Packer, and J. Vaughan, J. Am. Chem. Soc., 81, 4226 (1959); (h) Sheppard, W. A.,J. Am. Chem. Soc., 84, 3072 (1962);85, 1314 (1963); (i) Liotta, C. L., Chem. Comm.,7, 416 (1968). 6. cf. Lit. references for Table VI, set 10. 7. cf. Lit. references for Table VI, set 1. 8. cf. reference 2p. 9. cf. reference 2p. 10. cf. Lit. references for Table 11, set 7. 11. cf. Lit. references for Table XI, set 8.
11.
6. 7. 8. 9. 10.
5.
2. 3. 4.
1.
No.
~
TABLE XI
.03 .06 .06 .06 .09 .07 .10 .16 .04 .06 .07
SD
4
.ll .ll
.04
.147 .059 .lo6
.050
Data for NMe,, SCF, and SF, not included, no R values listed. Data for SCF, and SF, not included, no R values listed.
.10 .05 .20 .17 .15 .25 .12 .06 .12
.09 .03 .ll .11 .13 .24 .09 .05 .13
.174 .046 ,122 .113 .123 .068 .186 .111 .143
.150a .043 .123b .094= .1 1gC .114 .182 .056a .132a
.01 .09
.Olla .160a <.01 .08
.111 .195
.04 .10 .10 .03 .ll .12 .15 .15 .09 .09 -13
.126 .110 .lo0 .135 .081 .082 .050 .I 34 .076 .135 .127
.05 .06 .06 .10 .07 .09 .06 .29
.085 .155 .130 .042 .I09 .090 .098
.03 .08 .08 .03 .10 .10 .12 .ll .07 .05 .10
.093 .111 .097 .087 .lo1 .067 .084 .076 .077 .073 .077
SD
f
S&L SD
f
0;
SD
f
OR(A)
SD
f
OR(BA)
SD
f
a Datum for NMe, not included, no R value listed.
5. 6. 7. 8. 9. 10. 11.
4.
1. 2. 3.
No.
Values of SD and f = SD/RMS for Meta Basis Sets
TABLE XI1
u(m )
.168 .070 ,220 .154 .127 .119 .231 .079 .127
.037 .181
f
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
31
An, n, SD, f values obtained for each on fittings with the u i values of Table V. In Table XII, the comparative values of SD and SD/RMS are given for each of these reactions for fittings to all of the various substituent parameters. As expected from the fact that Am values are small (-.3-.5), the meta data are not discriminating. Three of the eleven meta basis sets are best fit by the u i values (Table XII); two sets are essentially equally well fit by u i and ; two sets are best fit by two sets are best fit by u ~ (; and ~ two ~ )sets are best fitted by the Swain and Lupton parameters. All fits are near the 10% level. Interestingly, the only F value below .I00 is that from the u i fitting. One must conclude from these results that whle the assignment of meta substituent effects to the sigma zero type is not inconsistent, the available meta data provide no sound basis of support for the unique applicability of the u; scale to meta series. Indeed, a scale derived from the 11 meta basis sets does not fit the meta sets significantly better.
E. u i Values Brown and Okamoto have defined u+ based upon the rates of solvolysis of p-substituted t-cumyl chlorides and demonstrated their applicability to a number of “electrophilic type” reaction rates and equilibria (2c, 15). The parameters have also been used by Yukawa and Tsuno in their dual substituent parameter treatment of such reactivities (2g, 16). Unfortunately, however, the t-cumyl chloride solvolysis series does not meet the requirements for a minimal basis set. Only one existing reaction set was found which satisfies this requirement, Eaborn’s protonolysis rates of p-substituted phenyl trimethylsilanes (1 7). Through use of Eaborn’s series, it was found that widely varying sets of u i were generated with very similar precision by use of various assumed constraining conditions, including values of A p . In the absence of independent evidence on the correct value of AP and, in the light of the moderate to poor fits achieved with most of the generated u i sets when applied to other reactions, an alternate procedure has been utilized to obtain the basis u i parameters. The pT values are well defined for both the Brown and Eaborn sets. In view of the approximate but general relationship, p y p y , obtained for other types of reactivities, a similar relationship was assumed. It was then noted that if uI; value were calculated by the relationship p y = p f s p g , or u1; = [log (I?/ k 0 ) / @ ] - of,the results were consistently (irrespective of the value of uf)20% smaller for Eaborn’s set than for Brown’s set. That is, if for Brown’s set APE 1 .OO, then for Eaborn’s set h p Z 30. Using these constraints, averaged ug values were obtained from the two data basis sets. The results were compared with u g , uR(BA)and values. Differences of a few hundredths of a unit found for most +R substituents between .I;, uR(BA)and u i sets were then averaged out (giving the results in Table V) with n o significant loss of precision
t 4
W
17.
15. 16.
14.
13.
10. 11. 12.
6. 7. 8. 9.
5.
II
Arc-CHN; + OAc- + C,H,COCH,OCOMe, HOAc, 40"
+
Protonolysis ArSiMe,, aq. MeOH-HClO,, SO" Solvolysis, ArCMe,Cl, 90% aq. acetone, 25" Solvolysis, Ar(C,H,),CCl, 60% Et,O -40% EtOH, 60" Acetolysis, 2-Ar-2-Me Propanol Brosylates, HOAc, 75" Acetolysis, 6-Subst.anti-9-ArNorbornenol Brosylates, HOAc, 77.6" Decomposition ArN: ArOH, H,O, 29" Coupling ArN; + 2,6-Naphthylamine Sulfonic Acid, H,O, 20" 0
Ionization, Ar,COH, aq. H,SO,, 25" Ionization, Ar,C(C,H,)OH, aq. H,SO,, 25" Ionization, ArC(C,H,),OH, aq. H2S0,, 25" Ionization, ArCHOH*, aq. H,SO,, 25" Ionization, ArC(OH)Me', aq. H,SO,, 25" Ionization, 4-Subst. Pyridinium Ions, H,O, 25" Ionization, ArCO,H, H,O, 25' Equilibrium, A r g + 2 0 H - + ArN, 0-, H,0,25" Ionization Potentials, ArCH,(g), eV.
1.
2. 3. 4.
Reaction
No
-2.317 2.722 2.522
-2.407 -4.086 3.994
-.666
-2.948
-3.902
-.841
-4.498 -4.657 -2.432
-9.793 -7.896 -5.557 1.999 1.981 2.688 .474 5.342 1.082
-5.474 -4.639 -2.718
Rates
-11.100 -8.085 -4.521 1.733 2.260 5.153 .627 6.566 1.045
Equilibria
.79
-.67 .63
.96
.76
.82 1.oo .89
.88 .98 1.23 1.15 .88 .5 2 .76 .81 1.04
Sigma R Plus Series. Fits to Eq. (1) with Use of uiValues
TABLE XI11
.I2 .07 .I4 .02 .25 .I0
6
4
5
4
6
11 12 7
5
6 13 5 8
.042
-.713
.986 2.892
,081 .023 .20 .04
.01
-2.31 8
-3.427
-4.462 -4.714 -2.504
1.909 2.037 2.993 .5 05 6.555 1.115
-5.204
-9.861 -7.844
P
.045
,031
.070 .075 .119
,059 .032 .170 .lo8 .067 ,060 .074 .094 .196
3'
.06
.06
.2 1 .15 .I 3
.75
7 4
5
.55 .23
SD
7
n
W
W
Decomposition ArCON,, Toluene, 65.2" -.140 Rearrangement Ar(Me)C = NOH, 1,4dichlorobutane, -4.440 70" Cannizaro Reaction, ArCHO, 50% aq. MeOH, 100" 4.426 Bromination, Subst. Durenes, MeNO,, 30" -7.839
2.1 27 -7.523
+.134 -3.361 .48 .96
-.96 .76
7
5
5 9 .I4 .27
.o 1 .14 .060 .087
.062 .088 2.249 -7.072
.046 -3.701
1. (a) Deno, N. C., and A. Schriesheim, J. Am. Chem. SOC., 77, 3051 (1955); Deno, N. C., H. E. Berkheimer, W. L. Evans, and H. J. Peterson, J. Am. Chem. SOC.,81, 2344 (1959); (b) Arnett, E. M.,and R. D. Bushick, J. Am. Chem. SOC.,86, 1564 (1964); (c) White, W. N., and C. A. Stout, J. Org. Chem., 27, 2915 (1962); (d) Schuster, I. I., A. K. Colter, and R. J. Kurland, J. Am. Chem. SOC., 90, 4679 (1968); (e) Knuteson, G., and R. W. Taft, unpublished data. 2. References (a), (b), (c), (d) and (e) for set 1. 3. References (a), (b), (c), (d) and (e) for set 1; Diffenbach, R. A., K. Sano, and R. W. Taft, J. Am. Chem. SOC.,88, 4747 (1966). 4. Yates, K., and R. Stewart, Can. J. Chem., 37, 644 (1959). 5 . Stewart, R., and K. Yates,J. Am. Chem. SOC.,80, 6355 (1958). 6. cf. Wells, P. R., S. Ehrenson, and R. W. Taft,Prog. Phys. Org. Chem., 6, 147 (1968). 7. Goodman, J. F., P. Robson, and E. R. Wilson, Trans. Faraday SOC.,58. 1846 (1962). 8. Lewis, E. S., and H. Suhr, Chem. Ber., 91, 2350 (1958). 9. Harrison, A. G., P. Kebarle, and F. P. Losing, J. Am. Chem. SOC.,83, 777 (1961). 10. Eaborn, C., J. Chem. SOC., 4858 (1956); Dean, E. B., and C. Eaborn, J. Chem. Soc., 2299 (1959); Eaborn, C., private communication. 11. Brown, H. C., and Y. Okamoto, J. Am. Chem. SOC.,79, 1913 (1957);80,4964 (1958). 12. Nixon, A. C., and G. E. K. Branch, J. Am. Chem. SOC.,58,492 (1936). 13. Heck, R., and S. Winstein, J. Am. Chem. SOC.,79, 3422 (1957). 14. Tanida., H.., T. Tsuii. - . and H. Ishitobi, J. Am. Chem. SOC..86. 4904 (1964). 15. Crossley, M. L., R. H. Kienle, and C. H. Benbrook,J. Am. Chem. SOC 62, 1400 (1940). 16. Zollinger, H., Helv. Chim. Act., 36, 1730 (1953). 17. Tsuno, Y.,T. Ibata, and Y . Yukawa, Bull. Chem. SOC.Japan, 32, 960 1959). 18. Yukawa, Y., and Y. Tsuno, J. Am. Chem. SOC.,79, 5530 (1957). 19. Husigen, R., J. Witte, H. Walz, and W. lira, Ann., 604, 191 (1957). 20. Tommila, E., Ann. Acad. Sci. Fennicue, A59, 3 (1942). 21. Illuminati, G . , J. Am. Chem. SOC., 80, 4941,4945 (1958); 78, 4975 ( 956).
20. 21.
18. 19.
P
w
-1.53 -3.79
-.612
-1.827 -.569
- .45 1
Pg
-6.247 -7.231 -7.441 -7.914 -1 1.283
-19.43 -8.41
C"-nmr Shifts
-6.419 -7.862 -7.869 -7.913 - 10.746
F-nmr Shifts
-.438
-1.792 -.272
-.680
p4)
12.7 2.22
.97 .92 .95 1.00 1.05
1.40
1.02 2.10
.66
AP
6 6
6 6 5 7 7
11
1.62 .79
.19 .21 .06 .36 .83
.04
.096 .112
.068 -065 .018 .089 .096
.097
.083 .053
.08 .03
8 10
.034
.01
5
f
SD
n
-8.09
-18.36
-6.056 -6.973 -7.249 -8.086 -11.36
-.610
-1.801 -.554
-.640
P
Jones, B.,J. Chern. SOC.,1854 (1936). Smirnov, Y. D., S. K. Smirnov, and A. P. Tomilov, Zh. Org. Khim., 4(2), 216 (1968). Goering, H. L., and R. R. Jacobsen,J. Am. Chem. Soc., 80,3285 (1958). White, W. N., D. Gwyn, R. Schlitt, C. Gerard, and W. Fife,J. Am. Chem. SOC.,80, 3271 (1958). Pews, R. G., Y. Tsuno, and R. W. Taft, J. Am. Chem. Soc., 89, 2391 (1967). Reference for set 26. Reference for set 26. Reference for set 26. Taft, R. W., and L. D. McKeever, J. Am. Chem. Soc., 87, 2489 (1965); McKeever, L. D., Ph.D. thesis, Univ. of Calif., Irvine, 1966. Ray, G. J., R. J. Kurland, and A. K. Colter, Tetrahedron, 27, 735 (1971). Reference for set 31.
Ar,C', H,SO,-H,O, 37" (C of C+center) Ar,C', H,SO,-H,O, 37" (C para t o substituent)
31. 32.
22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.
Arb-FC,H,)CO-BF, Adduct, CH,CI,, 25" Ar@-FC,H,)CO-BC13 Adduct, CH,CI,, 25" Ar@-FC,H,)CO-BBr, Adduct, CH,CI,, 25" Ar@-FC,H,)COH', H,SO,, 25" Are-FC,H,)CC,H:, CH,CN, 25"
O,
26. 27. 28. 29. 30.
25.
--f
Chlorination, ArCOC,H,OMe(-p), 99% aq. HOAc, 20" Cleavage, ArHgBr + HCI ArH, DMF, 17" O-Claissen Rearrangement, ArOCH,CH=CH,, 184.9", (C,H,),O OClaissen Rearrangement, ArOCH,CH=CH,, 181 carbitol
22.
23. 24.
Reaction
No.
TABLE XI11 (continued)
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
35
of fitting. For all -R type substituents, u i are significantly enhanced compared ~ ~ Any ) averaging of these values between to corresponding u i and u ~ ( values. sets is found to be accompanied by significant loss of precision (compare, for example, fittings summarized in Tables IV, VII, IX, and XIV) and consequently is not done in arriving at u i values for -R substituents. The u i values of Table V obtained in the manner described above are found to fit uniquely a substantial number of data sets within the criteria f < .lo. Indeed, the variation of XP and p y values permitted by these correlations is highly remarkable (XP varies from -.96 to 12.0, p y varies from -1 1.10 to -.140 and from t.627 to +6.566). Table XI11 lists values of p y , p$ , XP, n, SD, and f obtained for sets of the u i type, each of which contains data for sufficient numbers and kinds of p-substituents to provide a reasonably critical analysis. Table XIV lists comparative SD and f values for fittings of all the sets of Table XI11 with each of the U, scales of Table V, the F and R values of Swain, and with the single substituent parameter treatment, PO&). These statistics, coupled with structural considerations, we believe support the usefulness and uniqueness of a u i scale of “limited generality.” In general, the f values of Table XIV for the uI; scale are smaller than those of the other scales by factors of from 2 to 10. The root-mean-square F values for the other scales are from 2.25 to 3 to 4 ( S & L, u i , a&,,) times that for u;(. Because this analysis has demonstrated that Swain’s F and R are generally inferior for the discriminating data for all four types, there appears little to encourage proliferation of these parameters.
-
111. DISCUSSION
A. Regarding Fittings by Equation (1)
The fact that our analysis yields essentially the same precision of fit for reaction rates, reaction equilibria, and F-nmr shift data we believe is highly significant. That is, substituent behavior is indicated to be generalizable to a precision of SD/RMS=f = .05 to .lo. This result is in keeping with the basic idea that the substituent effects may, be described by parameters characteristic of the substituent group. To these three types of measurements may be added the C-13 and proton nmr shifts and the ir intensity measurements, for which fittings are generally only slightly less precise. Because the experimental errors in these latter measurements generally appear to be somewhat greater, the generality of the treatment of substituent electronic effects according to eq. (1) is not apparently damaged, but is in fact supported by the broad range of measurements involved.
m
W
SD
.55 .23 .75 .I2 .07 .14 .02 .25 .10 .21 .I5 .I3 .06
No.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
n i '
.059 .032 .I70 ,108 .067 .060 .074 .094 .I96 .070 .075 .I19 .031
f
f' .loo .206 .337 .196 .142 .I23 .I32 .I68 .339 .I86 .242 .241 .053
SD .88 1.48 1.41 .22 .I4 .28 .04 .45 .I8 .54 .5 1 .27 .I0
OR(BA)
TABLE XIV
1.94 2.23 1.87 .28 .18 .6 1 .04 .49 .21 .9 1 .68 .35 .21
SD
4 .220 .309 .447 .251 .I88 .263 .I48 .I83 .402 .318 .322 .317 .I08
2'
.43
.55
4.59 4.59 3.06 .45 .36 1.19 .09 .77 .30 1.86 1.08
SD
.510 .487 .221
.648
.519 ,637 ,733 .402 .371 .497 .323 .288 .573
f
u s Sets
,JR(A)
Values of SD and f = SD/RMS for
.84 .66 .53 .16 .I3 .41 .03 .51 .19 .55 .69 .32 .I4
SD
.I58 .046 .232 .113 .152 .383 .268 .179 .I38 .I56 .047
.I55 .208
1.40 .33 .97 .12 .15 .89 .07 .48 .07 .47 .lo
.17 .41
.I 1 6a .153a .260a .I47 .131 .195a .I19 .I91 .358 .280a .325 .284 .074
I' SD
"
6 I'
S&L
4
W
14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.
.045 .081 .023 .042 .064 ,088 .060 .087 .034 .083 .05 3 .097 .068 .065 .018 . I 23 .096 .096 ,107 1.34 2.52 4.40 .79
.48
.21 .08 .06 .31 .34
.02
.03 .o 1 .31 .24 .61
.I3
.I7 .36
.I30 .I45 .071 .090 .I01 .I93 ,107 .I96 .070 .223 .I68 .147 . I 1I .I04 .I45 .312 .293 .259 .I12 .28 .39 .22 .05 .01 .34 .46 .87 .02 .29 .I6 .I 1 .54 .71 .56 1.57 3.10 5.98 1.48
a Datum for NMe, not included, no R value listed.
.06 .20 .04 .01 .01 .I4 .I4 .27 .o1 .08 .03 .04 .I9 .21 .06 .52 .83 1.62 .76 .366 .360 .353 .210
.I71
.208 .I59 .I22 .I56 .I28 .211 .205 .280 .078 .311 .332 .281 .I92 .220
.47 .69 .43 . I3 .03 .66 1.04 1.47 .03 .37 .28 .20 1.05 1.26 1.37 2.36 5.67 11.22 3.95 .355 .281 .244 .370 .231 .408 .461 472 .121 .403 .598 .503 .387 .399 .415 .534 .627 .661 .559 .14 .24 .09 .03 .O1 .34 .04 .86 .01 .38 .09 .08 .7 3 .83 .50 2.07 3.23 2.45 .7 1 .481 .608a .242a .151a
.I51
.I04 .097 .05 1 .089 .05 1 .210 .019a .277 .048 .399 .229a .I98 .259 .257 .07 2.41 .6 1 .07 .I 1 .45 .89 .67 .08 .39 .I2 .I4 .23 .31 .20 .74 1.oo 7.15 1.97
.05 1 .978 .345 .200 .976 .275 .398 .217 .306 .418 .256 .343 .081 ,096 .062 .I 84 .I 17 .421 .278
38
S . EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
The physical property measurements pertain to a specific state of chemical identity, whereas the rate and equilibrium measures pertain to a change between such states. Consequently, eq. (1) is shown t o apply to either situation with essentially equal precision. The data sets with V ’ E p : /py values appreciably different from unity give such large deviations with the single substituent parameter equation (cf. Tables IV, VII, IX, and XIV) that the statistical best-fit parameters are essentially meaningless. However, the data sets with XP values which are either large positive numbers or negative numbers are treated by eq. (1) no differently from those more usual sets (with near unit W values) with respect to both statistics of fitting and of the appropriate structural classification of the type of OR scale giving best fit (cf. discussion of next section). This result provides critical evidence of the general applicability of eq. (1) with the four uR scales. It is important to note that the fitting according to eq. (1) requires zero .OO). While we intercept behavior: i.e., P‘ = .OO for H (for which uI uR recognize that the data for the unsubstituted (H) member of a set may be as subject to experimental error as any other member, such error is generally relatively small for a set of reliable data. Any constant error from this source will be distributed among all of the substituents in such a manner as to achieve “best fit.” Any loss in precision of fitting of the set which may result by such a procedure we believe is a small price to pay compared to the “violence” done by introduction in eq. (1) of a completely variable “constant” parameter. The latter procedure has been utilized by other authors both in treatments by the simple Hammett equation and by the dual substituent parameter equation. We specifically reject the inclusion of a third parameter as a constant intercept in eq. (I), even though the rejection does result in loss of precision fit. Our reasons are as follows. The third parameter gives unwarranted freedom in the fitting of the data. In a data set, the point P=O for the H substituent is a highly critical and valuable one in locating the scale origins. The hydrogen data point cannot influence the rho values (all sigmas are constrained to zero), and accordingly, the hydrogen data point is not explicitly counted in the statistics. Furthermore, the H atom has unique structure (perhaps the most different) among those of all the substituents (10). To in effect throw away this point in a data set (by introducing a third parameter) we believe is to render to the noise level one of nature’s most revealing signals. Many of the significant results of this analysis, which are discussed in the following sections, would have been lost had we not adhered strictly to eq. ( 1 ) . A note regarding the weighting of data by the least-square analysis by eq. (1) is in order. By not explicitly assigning weights to individual points or data sets, we have implicitly weighted the points by the size of the Pi value, or for the individual data set, by its RMS of P‘. This weighting is done because (a) we feel that a larger P is probably generally known more accurately than a smaller one
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
39
(we recognize that there are exceptions, of course) because the P"s are really differences (log k i - log Pi, or Pi - 8)and (b) we have no other knowledge of how to weight points without introducing bias. Consequently, even though our fittings are explicitly weightless, we must make adjustment for our implicit weightings. This adjustment is done by examining the fit parameter, .FSD/RMS: that is, by comparing f values for a given data set as obtained with the various (previously defined) sigma constants. We note here also that the comparison off values among basis sets used to define a particular OR scale is not profitable, because the fitting minimizes the overall SD for all points in all sets considered. Yukawa and Tsuno have discussed (16, 18) a dual substituent parameter treatment having greater freedom than eq. (1). In this treatment, they utilize one universal pi delocalization parameter, 71, and allow p n values for a given data set (one p n value for substituents in the +R class, and the second pn for substituents in the -R class). While this treatment has the potential to correlate data on a very broad basis, it suffers the important disadvantage that it cannot critically distinguish significant separations of polar and pi delocalization effects from nonsignificant or coincidental fittings. That is, eq. (l), as we have applied it, makes the separation of I and R effects by utilizing the noncorrelation between UI and U, values over the full range of electronic effects from extreme -R to extreme +R (in the plot of a, versus any of the OR parameters of Table V, points for a minimal basis set fall in a generally random fashion among three of the four quadrants). With the freedom introduced by the Yukawa-Tsuno treatment, the separation of I-R effects is based upon the noncorrelation between polar and pi delocalization parameters withm each class, -R or +R (i.e., generally within only one quadrant). Because of well established correlations between these parameters for certain common structural features within the -R or the +R classes (lo,), we believe that this treatment at the present level of knowledge does not rest upon very sound ground. (A similar objection applies to the Exner are required for treatment (20).) The present finding that four scales of precise description of p-substituent effects clearly does not appear to support the basic postulate of the Yukawa-Tsuno treatment: namely that a single generalized scale of pi delocalization parameters is applicable within either -R or tR classes.
B. Pi Delocalization Parameters and their Interpretations The UR parameters of Table V show many of the trends previously recognized (24 4, 10, 19). The substituents (-R) having a first row element with an unshared electron pair as first atom (F, OCbH5, OMz, NHCOMe, NHZ and NMez) show enhanced pi delocalization across the scales: i.e., -u: < -uR(BA) < - u i . The increment of the scales is greater between -UR(BA) and - u i than between -ug and -uR(BA), although this trend
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
40
increases sharply in the sequence of substituents given above. For the weaker pi but donor substituents (Me, C6H5, C1, Br, and I) -UR(BA) < - u i -uR(BA) = -ug . For unsaturated substituents containing electronegative atoms (+R), ui(A, > ug Z uR(BA)Z u i is a completely consistent pattern, extending from the weak pseudo-unsaturated substituents, e.g., SCFJ, SiMea, SF5 and CF3, to the relatively strong unsaturated acceptor substituents, e.g., CN, CO1 R, NOz and CH3C0. More specific orders are found in specific instances. Thus N
-oi(A) =
-4< -oR(BA)
for NH2 and OMe, but for F - u ~ ( A ) = -uR(BA)
> -0; .
This special propensity of F for pi donor action in electron-rich systems has been previously discussed (20). For the substituents Me, C1, and Br, -u;;(~, E - u ~ ( -= ~ -~a0R) , but -u: >
for SMe and I. The latter feature has been ascribed t o the presence of unoccupied acceptor orbitals (probably d ) (14). The same relationship may apply for C1 and Br, but the effects are too small to be significant in the definition of the scales. The C6H5 substituent has been considered as having the ~ u) i, values are capacity of either a donor or sink. In accord, u i , u ~ ( ~and negative for C6H5, but u ~ ( A )is positive. Aside from the OH substituent, which was specifically not considered in this analysis becausi of the evidence of marked and specific hydrogen-bonding effects (2b, lo), the only substituent which does not appear to behave acceptably according to eq. (1) is SMe. The behavior of this substituent appears acceptable in all but the u i sets. (The behavior of this substituent in the a; TABLE XV Calculated u i Values for SMe
Reaction
PR
1 3 6 10 11 21 21 28
-9.79 -5.56 2.69 -4.50
-4.66 -7.52 -7.91 -11.28
-.55 -.48 -.66 -.69 -.81 -.64 -.98 -.95
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
41
scale cannot be regarded as well tested, however.) The inadequacy of a fixed u i parameter for the SMe is illustrated in Table XV, which gives values calculated according to eq. (1) for each available set. The inability of a single u i value to describe the behavior of the SMe substituent may be the consequence of two pi interaction mechanisms at sulfur (14,21): e S + - M e
and
+O
E - M e .
However, the iodo-substituent, which might be expected to show similar behavior, is well behaved. The behavior of the substituents MeSO, SCF3, and CF3S0 would be instructive in this connection, but no data exists for these substituents in any of the u i sets. The substituents NHCOMe and OC6H5, which involve competing conjugative interaction mechanisms, as well as coplanarity problems, are only moderately well behaved in the u i sets. Calculated values of c i vary from -.74 to -.86 for the former and -.74 to -.92 for the latter. There is, however, a considerable presumption in the case of the NHCOMe substituent that this behavior is solvent related. The value -.74 (reaction 6 ) is obtained in water solvent at 25", and the value -.86 (reaction 23) is obtained in dimethylformamide solvent at 17". The UR(BA) values calculated for the NHCOMe substituent show similar trends with solvent, as shown in Table XVI. Evidence has been presented from F-nmr shielding effects in m- and p-substituted fluorobenzenes (10) that solvent interaction modifies the uz values of a number of the substituents of Table V (specifically NMez, NH2, NHCOMe, OMe, CH,SO, SF3, CF,SO, CF,, S03ME, CN, COzR, NOz and MeCO). The indicated changes in uI between hydrocarbon and weakly protonic solvents are TABLE XVI Calculated UR(BA) Values for NHCOMe
Reaction
Solvent
PR
u~ ( BA)
1
H,O, 25" H,O, 25" 10%aq. EtOH, 25" 15%aq. EtOH, 25" 50%aq. EtOH, 25" 50%aq. EtOH, 25" dimethylformamide 75%aq. EtOH, 25" 80%aq. Me cellosolve
1 .oo .87 .95 1.93 1.21 1.21 -3.32 1.31 1.44
-.26 -.34 -.33 -.34 -.39 -.39 -.41 - .44 - .46
16 4 28 2 3 40 5 6
S . EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
42
Q.05. In the statistical fittings of reactions, we did not find significant
improvements in correlations utilizing these indicated solvent-effect variations in sigma constants. Consequently, we have utilized throughout this analysis the constants for weak protonic solvents and have allowed any solvent-substituent influences to be reflected in the PI and p R values. This procedure unquestionably oversimplifies the treatment of substituent-solvent interactions (as is indicated by the results for NHCOMe in Table XVI), but when the effects of these interactions are relatively small, the statistical results indicate that the treatment is permissible to the precision we have discussed. For the fittings of p-substituted fluorobenzene F-nmr shifts, the p values do reflect the generally expected effects of methanol-substituent interaction (10) (in cyclohexane, pf = -7.30 and p g = -30.8; in methanol, pf = -9.02 and ppR = -31.2). Additional discussion of solvent effects on p values is given in a subsequent section. In this paper, we have not concerned ourselves with the differing behavior of various alkyl groups, but have instead for the present considered the methyl substituent as roughly representative of the behavior of most alkyl group substituent effects. The present results make possible (through use of pIand pR values) analysis of reported substituent effects of various alkyl groups. Such an analysis is beyond the scope of this paper, however. We infer from the results of our statistical analysis that the four UR scales of Table V are definitive and characteristic of the substituent interacting within a given pi framework. The pi interaction frameworks suggested are as follows (2P, 22):
1. The G: Scale X
o
Y
' X O -Y ,
+-.-.-+
or
-
I (X is a general substituent, Y is a detector or reaction center.) The inclusion of p-substituted fluorobenzene F-nmr shifts in the u i basis sets suggests that weakly interacting Y pi electron donor groups are also permitted.
2. The uR(BA) Scale X
G
Y
- 0.+x-- __._.
Y is a weak to moderate pi electron acceptor group. Examples of Y groups from Table IV include, in addition to carboxylic acid and derivative groups, S02NHR, Se(OH), , As(OH)~, As(OH)~O-, COC6H4F@), S F S , C6H4F@), SC6H4F@), and CH2F. The groups apparently all possess weak pi electron acceptor orbitals. The CH2F group can presumably act as a weak acceptor
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
43
through the contribution of the hyperconjugative form: \----I
-
3. The 0; Scale +
X -O
Y
Y is a strong interacting pi electron acceptor. In addition to carbonium and oxocarbonium ion centers, examples of Y groups from Table XI11 include N l and several electrophilic substitution transition states (cf. sets 10, 21 and 23) of the type
The pyridium ion interaction is also included, although the low hP value (S2) for this ionization (set 6) is in accord with a lesser stabilization of forms, e.g.,
than the corresponding trans quinoidal forms (above), cf. subsequent discussion.
4. The u;i Scale
Y is a strongly pi electron donor group. As previously noted in the results section, examples of Y from Table VI include centers of high pi electron charge density at carbon, sulfur, nitrogen, and oxygen. Also included in Table VI are examples of nucleophilic substitution transition states (cf. reactions 21 and 22) of the type
-.a;, -
It is interesting to note in the latter connection that nucleophilic substitution transition states in which there apparently is not strong delocalization of pi electron density into the substituent tend to fall into the ug type (cf. reactions 18 and 19 of Table VIII). In set 18, there are two ortho nitro groups which apparently take up much of the pi charge (thus it is unavailable to X), whereas in set 19, the positive piperidinium center may cause (perhaps with assistance from the 'NH hydrogen bonding permitted by the aprotic solvent) the
44
S. EHRENSON, R. T.C. BROWNLEE, AND R. W. TAFT
single ortho nitro group to exert a similar influence. Another interesting example of a nucleophilic substitution transition state for which the data clearly discriminates in favor of the u i rather than the UGCA) type is in the methoxydechlorination of cata-substituted 4-chloroquinolines. Evidently, the transition-state interaction structure MeO.. $1
is substantially more important than the structure
as seems reasonable on other grounds. (Compare, for example, pR values for the F-nmr shielding effects of 4-substituted 1-fluoronaphthalenes with 7-substituted lp-fluoronaphthalenes (2p). The fitting results for this rate data set (X-NMe2, OMe, SMe, Me, F, C1, Br, and NO2) are as follows:
4 SD
fa a
.09
.on
~R(A)
.34 .286
UR(BA)
.14 .I20
0;
.31 .260
RMS = 1.20 for all parameters.
It is apparent from these examples (and the previous ones) that the dual substituent parameter treatment appears to provide an important potential means of characterization of aromatic substitution (and other) transition states. C. Concerning OR Type and Values of the p R Parameter
In rate or equilibrium state changes, we presume that generally one state is dominant in determining the OR type (for example, in the ionization of ArNH;, the dominant state is ArNH2, or, in the ionization of ArJCOH, the dominant state is Ar3C+). Because p R values for reaction rates or equilibria are thought to be related to the change in pi electron demand at the reaction center (2,23), there is no necessary relationship between the magnitude of the p~ value and the uR type. Tables 11, 111, VI, VIII, and XI11 show that wide variation in p~ values (and indeed of sign and magnitude of K values) are permitted within each type of OR scale. As noted in the results section, all of the F-nmr shift sets for p-fluorophenyl tagged systems are well behaved in both precision of fit and in
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
45
the structural relationships to the type of UR scale giving best fit. This fact indicates that the measurements of F-nmr shifts in both states corresponding to a reaction equilibrium will provide a revealing probe of the composite equilibrium substituent effect. For the formation of the BC13 Lewis acid adduct of p-fluoro-p'-substituted benzophenones in CH2C12 solution at 25",
substituent effect shifts have been obtained for the adduct state and the uncomplexed ketone state (23). From these, one obtains the substituent effect, f R A, on the state change corresponding to complex formation. These shifts are summarized in Table XVII.
TABLE XVII Substituent Effect F-nmr Shifts for BCI, Adduct Formation with p-Fluoro-p'-Substituted Benzophenones, CH,CI,, 25"
p'-Substituent Me0 C,H,O Me C,H, F
c1
CF, NO2
Uncomplexed ketone, ppm
BCI, adduct, ppm
Complex formation I R A , PPm
.91 .45 .45 .02 -.19 -.52 -1.32 -2.01
5.05 3.66 1.88 I .25 .18a -1.05 -4.25 -6.19a
4.14 3.21 1.43 1.23 .31 -.53 -2.93 -4.1 8
a Calculated shift, using
eq. (1).
The dominant state in the adduct formation is clearly the adduct. Further, the shifts for the uncomplexed ketone are best fitted by the UR(BA), whereas those for the adduct state are best fitted by u i , in accord with structural expectations. Because the adduct state is dominant in the complex formation equilibrium, the I R A values are also best fitted by the u i scale. The PR values for the individual states (summarized in Table XVIII) for this reaction (as well as other similar examples for BF3, BBr3 and H' adducts) are consistent with the idea that increasing pi electron demand at the reaction center increases the -PR
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
46
TABLE XVIII Fitting Results for Lewis Acid Complex Formation (a) Best fit parameter
4
4
Uncomplexed ketonea -2.71
-2.55
1.06
-7.23
-7.86
.92
-5.58
-5.28
1.06
BCI, Adductb IRA ~~~
Best fit parameter
kp
U ~ B A ) 01; 01;
~
(b) Fittings for I R A values ~R(BA)
U i
.22 2.68 .081
SD RMS
f a
.49 2.68 .I82
L
S
UR(A)
;0
.72 2.68 .269
.62 2.68 .233
1.22 2.60 .470
cf. Table 111, set 37 cf. Table XIII. set 25
value. While values for the F-nmr sets generally reflect a similar pattern, there is as yet no satisfactory theoretical model for these terms (2p). An additional example of this kind is also instructive: i.e., the following hypothetical oxidation “reaction”:
As noted previously, the shifts for the methane state (NO. 25 of Table VIII) are best fitted by u i and for the ketone state by UR(BA) TABLE XIX Fitting Results for
SD RMS
f a
--
Values for Oxidation “Reaction”
Ul;b
S&L
.07 .83 .08 1
.06 .52a .121
0
u
~
(
.18 .83 .212
Datum for NMe, not included, no R value. For best fit = -1 .I 62 and p; = - 1.025.
~7
~
~O R )
UR(A)
.27 .83 .324
.5 1 .83 .617
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
47
(Table XVIII). However, the $RA values corresponding to the oxidation reaction state change are best fitted by u i (cf. Table XIX). Thus we see that composite substituent effects for state changes may be complex, with neither state achieving clear dominance. That is, the c r i fitting is apparently characteristic of this particular state change, rather than an individual dominant state.
D. Concerning the Separation of Z and R Effects Data sets for which & /&=X p is very large can potentially provide an indication of whether UR parameters have been correctly defined (i.e., with no, or very little, I effect components). For example, any data sets for which I s 0 for all substituents would give rise to an apparent F’ value of finite value (rather than infinite) if the appropriate type uR parameter were incorrectly defined. In fact, for several such sets of data, the apparent V’ values would be essentially a finite constant. Table XX summarizes the hp values for all data sets having large V values. The results provide no evidence for incorrectly defined u i or u i parameters, because P’ values of Table XX are variable both in magnitude and sign. In the data sets for w h c h h 2 10, there is a considerable presumption that the pr terms may be largely artifacts. That is, for most practical purposes these sets may be regarded as sets with h p + w . One data set from the benzene series has been noted which represents the opposite limit: i.e., AP+ 0. This is the data set of Exner and Jonas (25) for the ionization of X-CH? - @-C02H in 50% aq. EtOH, 25’. There is essentially n o , with discrimination between the precision of fits to the U: , u ~ ( ~or ~u; ) scales TABLE XX kp Values for Data Sets Displaying Large Values
Set No.
AP ui
*15 *16 *21 22 *26 27
PP
p%
Type (cf. Table VIII)
3.46 4.22 -16.8 -31.7 3.9 15.9
-9.02 -7.30 10.1 4.2 -5.5 -1.3
-31.17 -30.82 -1 70. -1 33. -21.2 -21.2
u i T y p e (cf. Table XIII) 29 30
12.0 2.2
-1.63 -3.83
-19.54 -8.46
48
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
t h s data set, and hp values of -.02, -.01, and +.01, respectively, are obtained. The value of py is.903 k .010 with SD= .03 and f =.082 ( X = OMe, C1, Br, I, C6H5, CN, OC6HS, and NHCOMe). This result indicates that the interposed CH2 moiety does eliminate conjugation of the substituent, X, with the ring system (but not necessarily that of the CH2 group).
E. Variables Affecting h The data sets (above) with the large values of X p are physical property measurements which presumably involve predominantly the pi electrons. For example, the F19- and C”-nmr shifts are dominated by paramagnetic contributions resulting from unbalanced pi orbitals (24). Ionization equilibria, on the other hand, are characterized by a much higher blend of polar effects (a blend w h c h traditionally has been defined as hp = 1.00 for the ionization of benzoic acid, H 2 0 , 25’). h values clearly reflect the poorer transmission of pi delocalization effects from the meta than para position. For the select meta sets of Table XI, for example, Am is typically about .4, whereas for corresponding reactions, hp is around unity. Evidence is meager with respect to the ortho position, but it appears that in accord with the classical ideas of pi electron transmission in the benzene ring, generally X p > ho > Am for corresponding reactions (cf. subsequen t discussion). An important feature of eq. (1) is that it allows for the possibility that and PR may be of opposite sign (A = negative quantity). A basic question may be asked: Are I effects transmitted through bonds in such a manner (via direct pi electron transmission or indirect pi-sigma electron interactions) that the I and R effects of any substituent must always necessarily be directly related? The data sets having hP values which are finite negative quantities provide a definite answer of no t o this question. These data sets provide critical evidence that I and R effects may have a high degree of independence. A set with a negative hp is one in which, for example, a substituent with positive values of both urand uR has polar and pi delocalization effects which are opposed: i.e., are opposite in direction. Three reaction rate sets (no. 34 of Table 111 and nos. 15 and 18 of Table XIII) have been found which show this relationship, and the behavior appears quite rational (26). These reactions are such that in going from reactant to transition state, positive charge is moved closer to the substituent (therefore negative values of p y are expected, as observed). These reactions are further characterized by a loss of reactant state para quinoidal resonance stabilization on achieving the reaction transition states. Therefore, because direct resonance effects predominate over indirect or resonance polar effects, positive ppR values are expected, as observed. We have found no data reported for a chemical equilibrium series having
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
49
X p negative. However, there appears to be no reason to expect that such sets should not exist. That is, the absence of such sets is attributable to the lack of imaginative equilibrium studies rather than to any fundamental behavior of nature which prohibits such possibilities (except for u i type p-substituent effect equilibria and meta substituent effects generally, for which positive X values are evidently required). While certain types of structural changes at the reaction center appear to permit AP to take on a high degree of variability, other types of structural change lead to little or no change in X p . Thus, extending the chain of conjugation between the substituted phenyl ring and the reaction center for a given type of reaction with CH=CH or - G C - bonds has little effect on X p (compare the results for corresponding reactions of benzoates, cinnamates, or phenyl propiolates, Tables I1 and 111). Also, the F-nmr shifts for p-fluorophenyl tagged systems are sets with X p 1.0,irrespective of the moiety (a bond, C=O, C=OH+, CH2, CHOH, etc.) interposed between the p-FC61-L, and p'-XC6H4 rings. This result is in marked contrast to the fluorobenzene shifts in which both the F detector and the substituent are placed in the same ring. (Both the Am and X p values are then notably unique (lo).) There is a considerable presumption that steric twisting from coplanarity, which diminishes effective transmittal of pi-electron effects, has appreciable effect on X p . For example, the X p = 1.I0 for the phthalide saponification rate (no. 28 of Table 111) compared with X = .89 for the corresponding benzoate saponification rate is probably a reflection of the rigid coplanarity conditions imposed in the former structure. However, the reactions were carried out in differing compositions of H20-EtOH solvent, so that a solvent effect may also be involved. The ionization of benzoic acids shows a regular trend among basis sets, in decreasing X p values with decreasing water content of the solvent (cf. Table XXI). The decreasing X p values may apparently be ascribed to the decreasing importance of para quinoidal resonance interaction in solvents of decreasing polarity (10,27). However, it is clear from the p y and p g values (both o f which tend overall to increase with decreasing solvent polarity) that additional factors contribute to the solvent effects on these parameters. Additional examples in general agreement with this trend in Ap values for benzoic acid ionizations are found in Table 111. Further evidence supporting this suggested interpretation of the X p values of Table XXI is obtained in the lack of solvent dependence of Xp values for ionization equilibria which involve little or no para quinoidal resonance interaction of the type I -
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
50
TABLE XXI Basis Set Ap Values for Benzoic Acid Ionization Reaction No. Solvent
AP 0%
4
7
1
4
2&3
6
H,O
10%aq. EtOH
50%of EtOH
80%aq. Me cellosolve
75%aq. EtOH
benzene
.87 .95 1.08
.80 1.24 1.55
.84 1.44 1.72
.I5 1.31 1.75
.69 1.36 1.98
~
1.01 (1.00) (1.00)
-
5
-
-
For example, in Table VIII, K values for ionization of ArCH2COzH are .87 k .02 in HzO, 10% aq. EtOH, and 50% aq. EtOH; for ionization of ArCHzNH;, Ap = .99 f .01 in HzO and 50% aq. EtOH. Also, in TableVI, Ap = .80 f .01 for the ionization of ArSH in 48% aq. EtOH and 95% aq. EtOH. Incidentally, the nonunity values for many X p noted throughout all of the correlations of reaction rates and equilibria by eq. (1) may be taken as evidence for the reasonable expectation that various changes in electron demand at the reaction center need not require equal responses of the polar and pi delocalization effects. instead, the nature of the functional group and its chemical change does influence the blend of ZP and RP effects. It is of course probable that in some of the data sets, especially those not fully represented by I OR values, contain experimental substituents with a broad spectrum of Uand errors or small specific effects which have given rise to fortuitous rather than well defined X p values. Clarification can be expected only from more rigorous experimental results for these series.
F. Ionization of Phenols in Water This reaction has been regarded by previous authors as the prototype of ureactions (2,28). It also figured heavily in the definition of the u" parameters of Wepster for -R para substituents (2e). However, we find that the data set for this reaction series is not fitted with acceptable precision by eq. (1) and u ~ ( A ) parameters (SD = .17, f = .130). Nor are the data fitted even as well by other parameters (for uR(BA), SD= .43, f = .329; for S & L parameters, SD = .38, f = .287). Thus, the data for this set appear truly exceptional. The largest deviations for individual substituents in the fitting with u ~ ( A )parameters are found among both -R (NMe2, NHz , F) and +R (NOz and MeCO) substituents. Because the data sets for both m-and p - substituents meet the minimal basis set requirements, we have utilized these in a manner similar to that described for the definition of ug(*) partfmeters to obtain a comparative set of uk(p) parameters.
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
51
TABLE XXII Comparison of u ~ ( and ~ )u&
Substituent NMe, NHZ OMe SMe Me
c1 Br I MeSO SCF SiMe, SF, CF, SO Me CN CO, R NO, MeCO
Parameters
UR(A)
O R (P)
-.34 -.48 -.45 -.I4 -.I I .04 -.45 -.23 -.I9 -.I 1
-.i6 -.25 -.36 -.04 -.06
-
.I4 .14 .20 .11 .38 .33 .34 .46 .41
.04
-.45 -.23 -.19 -.I I .17 .10 .17
.06 .08 .29 .24 .26 .46 .41
We stress that the latter parameter set serves only as a basis of comparison (cf. Table XXII), for we have found no evidence to claim any (even limited) generality for uj;(p) parameters. Table XXIII compares the fits with u i ( p ) and parameters for data sets of Table VI having six or more points. It is to be noted in Table XXII that u ~ ( A )= ui(p) (k.03) only for the halogens, C6H5,%Me3, NOz, and MeCO. It is evident that the uicp) values are appreciably more positive than the corresponding u ~ ( A )for all the other -R substituents (NMe2, NH2, OMe, SMe, and Me). Where differences exist between these two scales for tR substituents, a&) parameters are less positive, however. A clearly anomalous result is the sequence of - u i ( p ) values NH2, NMe2 < OMe < F. There appears to be no ready single explanation of this behavior, especially because the ionizations of phenols in nonaqueous media are satisfactorily (and generally better) fitted by u ~ ( A )parameters (cf. nos. 12, 13, and 14 of Tables VI and VII). It seems likely that concomitant with the strong pi donor action of the 0- reaction center, the protonic H 2 0 solvent may hydrogen bond to substituents, e.g., NMez and OMe, resulting in some twisting of these substituents from ring coplanarity. Such concomitant action would give rise to
52
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
TABLE XXIII Comparison of Fits with u&
and u I Z ( ~ )Parameters
%(P)
UR(A)
NO.^,^
SD
f
SD
I 2 5 7 10
.24 .07 .11 .26 .18 .16 .17 .I5 .31 .35 .62 .10 .38 .41 .23 .04 .19
,133 .042
.03 .03 .14 .14 .03
11
12 13 14 15 16 19 22 23 24 25 26 a
.084
. I 04 .I65 .111 .I 11 ,092 -.I04 .089 .I91 .lo6 . I 33 .158 .068 .094 .223
.08
.10 .10 .28 .36 .7 1 .08 .I 5 .19 .25 .o 1 .I 1
f .o I 5 .018
.072 .058 ,030 ,058 .069 .063 .093 .092 .217 .084 .054
.065 .072 .030 .133
Set no. refers to designation given in Table VI. n is 6 or more for each set, cf. Table VI.
the diminished values of -OR(,,). A limited set of data (n = 7 , and not including either NMez or NH2) for ionization of phenols in 49% aq. EtOH (cf. no. 2 of Table XXIX) is somewhat better fitted by the u;i(p) (f= .044) than by u ~ ( A ) cf= .056)parameters. It is clear that more investigation is required to obtain a better understanding of these interesting differences in substituent effect behaviors. It should also be noted that the ionization of ArNHC6H5 in DMSO (no. 15 of Tables VI and VII) is poorly fitted by the u ~ ( A )treatment cf= .217). This result might be taken 'as an indication of the limitations of u ~ ( A ) parameters in strongly enriched pi electron systems. However, in view of the other successes given in Table VI, we have investigated other alternatives. In the fitting of this data set by the uiCA)parameter treatment, individual substituent deviations of k1.2 log units are obtained for the NOz and SOzMe substituents. Accordingly, fittings were attempted with either the NOz or the SOzMe data point omitted. The results are compared in Table XXIV. It is clear that the data points for both NOz and SOzMe are incompatible with the treatment by eq. (l), as without one or the other, the precision is
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
53
TABLE XXIV Fitting Results for Reaction no. 15 of Table VI with uR(*) Parameters
SD All substituentsincluded ( n = 6) .71 NO, point omitted .I9 S0,Me point omitted .28
f .217 .lo1 .087
5.09 3.83 6.09
4.99 4.04 5.64
.98 I .06 .92
improved to an acceptable level. It appears most likely that the SOzMe substituent shows anomalous behavior. Until this matter is clarified, the fitting parameters (py, p c and h p ) for this reaction obviously must be regarded as highly uncertain.
G. Regarding Independent Generation of uIand OR Parameters It was desirable t o test for possible inadequacy of the uI values for certain substituents. This testing has been done with data for several reaction rate and equilibrium series for which both the p and m- sets meet the minimal basis set requirements. The PR and PI values for the m- and p- positions obtained in preliminary fittings were held as constraints in the data, with the result that both q and UR values were generated from best fitting. These sets of substituent parameters are dependent upon the q values of Table I in one respect only: namely, in the pI and p R values generated by the preliminary fittings as the constraints. This procedure then allows for the detection of any clearly errant substituent parameters. For example, the finite uR values for the CF3 substituent have been questioned (29) on the basis of an errant (too small) value of uI. However, the substituent parameters generated from individual reaction series by this procedure (cf. Table XXV) are in good accord with the values of Table I. Accordingly, the results of this treatment provide no evidence of inadequate or errant u~values. H. “Secondary” uR Values
From the p$ and py values of Tables 11, VI, and VIII, data for additional substituents may be used to obtain the various uR parameters. A number of “secondary” substituent parameters so derived are summarized in Table XXVI. The OR values are rounded values obtained from the indicated data. The uI parameters are based upon m-FC6H4X F-nmr shifts. The results in Table I1 are “untested,” of course, and should be used with due caution.
4
NO,
MeCO CO,R I Br CF, CI F CN
OMe
a
.56 .65
1 .ooo ,286
I .ooo 1.009
.I 2 .09 .04 .I 8 .29 .28 .33 .33 .4 1 .45 .38 .42 .45 .51 .67
.06 .I0 .I2 .23 .26 .27 .38 .30 .39 .44 .45 .46
.so
.oo
-.03
BA. I b
.oo
-.04
OF
1.990 2.167 1.377 .707
2.523 2.302 2.238 .7 30
.45 .44 .5 7 .67
1.781 1.709 1.478 .637
.4 1 .42 .67 .70
.4 3
Constraints
.34 .38
.4 3
.46 .4 1 .45 .48 .53 .65
.26
.25
.40
.08
.oo .I 3 .I 1 .I 7 .22 .26 .24
-.07
.oo
BA. 8b
-.01
BA. 7b
.14
.oo
-.11
BA.6b
Values Generated From Some Basis Sets
rn- andp- basis sets for ionization ArOH, H,O, 25".
Basis sets from Table VI.
From Table I. Basis sets from Table 11.
NH, SMe NHCOMe
C.85
Me H me*
Substituent
UI
TABLE XXV
2.990 2.720 3.100 .710
.27 .23 .27 .39 .42 .47 .47 .40 59 .65
.I8 .I 1 .26
.oo
-.01
A. 1'
2.676 2.426 2.000 .565
.48 .5 1 .52 .67
.23 .20 .31 .42 .46
.I 0
-.01
.oo
-.07
A. l I c
.oo
2.499 2.249 2.526 .468
.21 .24 .22 .45 .4 8 .45 .44 .43 .56 .61
.08 .I 1 .10 .25
-.02
P. I d
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
55
TABLE XXVI "Secondary" Substituent Parameters Substituent OCF, CH,CF, N(CF,), C(OH)(CF,), CF(CF,), SO,NH, CH=CHNO SO,F SO,CF, CH=C(CN), C(CN)=C(CN),
4 -.2Ia -.04e .0oe
.0oe .02e .05' .I 3a
u
~
-.31b (-.04)f
.0Ob coot .02 .0Sh -
~";(A)
~
-.2Ic -.04g
uI
--.21d
.55 .14 .48 .35 .48 .44 .24 .82 .84 .43 .6 1
-
.oog
-
.07' .I 2c -
.5 3d .3Sd .4ld
-
.49g .57! .68! .94'
k
~ O R (P) )
-
-
a Obtained from data of sets 15 and 16 of Table VIII.
Obtained from data of set 2 of Table 11. Obtained from data of sets 1 and 7 of Table VI. Obtained from data for ionization of ArOH, H,O, 25". Obtained from data for set 16 of Table VIII. Suggested value only. Obtained from data of set 1 of Table VI. h Obtained from data of set 1 of Table 11. ' Obtained from data of set 15 of Table VIII. j Obtained from data of set 7 of Table VI. Calculated from meta F-nmr shift relationship: = -7.10 or+ .6 (cf. reference 10). H
7
I. Additional Applications Eq. (1) has potential application t o other types of measurements of substituent effects besides those specifically considered in this paper: e.g., nmr coupling constants and shifts for other nuclei, ir and uv spectral shifts and intensities. We caution (with emphasis) in these applications the needed use of data sets of high quality, both with respect to the precision of the measurement and substituents considered (i.e., a full complement of substituent UI and UR properties must be encompassed for a meaningful correlation to be obtained). There is, of course, no requirement that all data sets will be uniquely fitted by eq. (1) using one of the four OR scales of Table V. For example, the data for the ionization of the conjugate acids of pyridine-N-oxides (30), HzO,25" is found to fit equally well the UR(BA) or ;u scales (SD=.14; f = .072). The data (31) for the rates of alkaline (-OMe) cleavage of ArSnMeJ are not fitted to acceptable precision cfs > .23) by any of the uR parameters. This data set is nevertheless indicated
vI
QI
0.5
Y
-'.O
-0.5
'-.& o;-.
.do
io o;.
/"
Me
= 1.976
.io S'O
PR 10.69 1.355
p,
J
Figure 1. Ion-Pair Formation, ArCO, H + (C, H, NH), C = NH, Benzene 25" ordinate (both figures): log (K/K, 1. abscissa: (upper figure, ub);lower figure, C from UR(BA) scale.
0
- 0.0
zY m0 . 5 1
I.o
"i
-1.0
-0.5
-g 0.0
Y
Y
0
I
-it .o [:
-A0
I
-20
00
.OO .20 40
I
/ I
I
I
1.00
.20
P,;:
PI = 9.30
.60 .80
CN
/..
.40
I
I
Figure 2. Fluorine Nuclear Magnetic Resonance Shifts, ArCH, F, C a , ordinate (bothfigures): &- x, ppm. abscissa: upper figure, u b ) ;lower figure, d from OR(BA) scale.
-0.0
-4*o-/
-4.0
i, 0.0
-
O.ol
.
-.60 "
.60
y
OMe
-20 .OO
O
Me
3 8
N
.20
I
-0.4
.40
I
aoo
2.628
,
.60 .80 1.00
I
x I
I
1.2
a8
p,=2.110 =0.80
PI
0.4
u-
I
0
O U
A u0
1
,
1.8
ub),
Figure 3 . Ionization, ArSH, 48%aq. ETOH, 25" ordinate (both figures): log (KIK,). abscissa: upper figure, a@), uG); lower figure, d from crR(A) scale.
0
Y
\
2.401 I .80
S0,Me
Y
ub),
-.2
-8
1
I
.4
I
.2
.4
1
0
0
-.4
I
.6
I
.8
I
I
.8
I
I
1.6
= 5.855 = 5.03I = 0.06
1.2
Figure 4. Rate, Displacement of CL- by-SC, H, in MeOH, 35" ordinate (both figures): log (klk,). abscissa: upper figure, u@), ub);lower figure, 6 from uR(A) scale.
6.0
58
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
O’O -1.0
1
H.
Me.
Not
CI
-4.0
OMe
1
180
1.0
0.0
2 -1.0 t -3A
I
I
-.a-.40
I
-.20
a
I
I
.40
0.00 .20
/
1
.60
.00
/ &t
OMe
3
-.a-.40
P, ~4.086 p, ‘9.722 *-.66
I
-.20 .OO
.20
I
.40 .60
Figure 5. Rate, Decomposition ArN,’, H,O,29” ordinate (both figures): log (k/k,). abscissa: upper figure, uIip);lower figure, G from u i scale.
to be interesting in that the fittings give values of X p ranging from .27 for the aj&) scale to .01 for the a; scale. The possibility is suggested that this data may reflect unique phenyl anion type pi delocalization effects (3 1). Unique resonance effects of meta substituents in radical cations have been indicated (32). It also seems reasonable that radical reactivities may be treated by a unique set (or sets) of pi delocalization parameters of “limited generality.” The UR parameter scales of Table V appear to be applicable to substituent effects at the ortho and meta positions. For the latter position, however, the data generally are not capable of discriminating between OR scales (cf. earlier results and discussion). For the ortho position, the great difficulty is in obtaining a data set covering the full range of electronic properties without the incursion of substantial proximity effect (2a) contributions. In a following section are reported some of the results of treatment of ortho data sets by eq. (1). Comparative plots are illustrated in Figures 1 through 5 with various
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
59
“ordinary” sigma values and with “synthetic” sigma values (6) obtained (2p) from the best fit to the DSP eq. (1). J. Solvent Effects on p y and
4 in Benzoic Acid Ionization 4
Through use of URR(BA)parameters for benzoic acid ionization, the p y and values given in Table XXVII have been obtained. Two important generalizations are found. For all pure organic solvents (e.g., benzene, n-BuOH, MeOH) p? /py r K 7 2 1.08. In mixed aqueous organic solvents (with the organic component greater than 15%by volume), K? 2 .95 (in H 2 0 and 10%or 15% aq. EtOH, KF = 1.OO). These generalizations hold without exception for all the solvents of sets nos. 2, 3, 5, 6, and 7 of Table I1 and for sets nos. 9, 10, 11, 12, 13, 14, and 15 of Table 111. The same generalizations hold for rates of esterification, ester saponification, and carboxylic acid reactions with diphenyldiazomethane (DPDM): i.e., sets no. 8 of Table I1 and nos. 26,27,34, and 35 of Table 111. It is of interest that set no. 34 involves a novel Ap value (-.37). The greater than unit value of KF in pure solvents is the result expected by the field effect model (33) on a distance basis. The lower than unit value ofK,“ in the mixed aqueous organic solvents appears to be related t o preferential hydration of the reaction center, which results in an increased effective dielectric constant from,the m- compared to the p position. The fact that KY values fall into two separate categories for pure organic and mixed aqueous organic solvents does not support the treatments of Exner (20) or Yukawa and Tsuno (16).
K. Ortho Substituent Effects No properly constituted data sets for reaction rates were found for which eq. (1) is followed with acceptable precision (34). This result may be attributed to the incursion of proximity effect contributions. However, certain benzoic acid type ionization equilibria data sets do appear to follow eq. (1) satisfactorily, although none of the sets qualifies as a minimal basis set. Table XXVII summarizes the results for the fittings with UR‘R(BA)parameters, which for every discriminating set provides the best fit (35). For sets nos. 1, 2, and 3 of Table XXVII, eq. (1) appears to hold for ionization of ortho substituted benzoic acids cf= .048 - .05S), with K; = &/pf = 1.6 .l. This result is reasonable for field effects transmitted only through the molecular cavity: i.e., the lines of force do not pass through appreciable solvent of high dielectric constant (the solvent is presumably excluded by the close proximity of the C02H center and the substituent) (36). It is further of interest that eq. (1) fails for the ionization of ortho substituted benzoic acids in solvents of high OH content (sets nos.4, 5, and 6 of Table XXVII).
*
0" .25 .43 .82
3. Ionization ArCO,H, 73.5% aq. dioxane, 25" 1S O .05 .057 OMe, Me,CI, Br, 1, H, NO, .97 .02 .025 Me, F, C1, Br, I, H, NO, .81 (1 .OO) .02 .041 OMe, Me, F,C1, Br, I, H, NO,
.66 .68 1.22
1.04 .60 1.24
1.03 .62 1.15
2.63 1.51 1.49
f.29 1.48 1.53
2.47 I .34 I .43
mP-
0-
mP-
0-
mP-
0-
P-
m-
.42 .46 .8 I
.45 .41
.07 .05 .04
.060 .059 .047
4. Ionization ArCO,H, 43.5% aq. dioxane, 25" 1.73 .I0 .I 10 OMe, Me, Cl, Br, I, H, NO, .94 .01 ,027 Me, F, C1, Br, I, H, NO, .02 ,040 OMe, Me, F,Cl, Br, I, H, NO, (1 .OO)
P
Me, F,C1, Br, I, H, NO, NMe,, NH,, OMe, Me, F , C1, Br, I, H, CN, NO, NH,, OMe, Me, F, C1, Br, I, H,CN, NO,
2. Ionization ArCO,H, n-BuOH, 25" 1 .I9 .09 .089 OMe, Me, F, C1, Br, I, H, NO, 1.05 .04 .066 Me, F , C1, Br, I, H, NO, (1 .OO) .o 1 .027 OMe, Me, F, C1, Br, I, H, NO,
I .48 1.09 (I .OO)
1. Ion-Pair Formation ArCO,H, -1, 3 DPG, Benzene, 25" .69 .33 .69
Substituents
2.03 .70 1.36
f
2.92 2.15 1.98
SD
0-
KI
PR
PI
Position h
Fitting Results for Benzoic Acid Type Ionization with ffR(BA) Parameters
TABLE XXVll
+
m
.18 .I 1 .44
.4 7 .4 3 .45
.4 3 .03 .03
,239 .051 ,050
.05
.30 .03
,261 .086 .I 10
25" OMe, Me, F, C1, Br, H, NO, OMe, Me, C1, H, NO, OMe, Me, C1, H, NO,
OMe, Me, F , C1, Br, I,C,H,, H, NO, (n = 19) (n = 20)
OMe, Me, F, CI, Br, I, H, NO, Me, F, CI, Br, I, H,CN, NO, OMe, Me, F,CI, Br, I, H , C N , NO,
35% aq. dioxane, 25" .I 98 OMe, F, C1, H, CF,, NO, .220 OMe, F, C1, H, CF,, NO, OMe, F, C1, H, CF,, NO, .217
7. Ionization trans-ArCH=CHCO,H, H,O, 1.02 .03 .I 77 .95 .03 .I44 ( I .OO) .05 .258
1.oo ( I .OO)
I
6. Ionization ArCO,H, H,O, 25"
1.09 (1 .OO)
5. Ionization ArCO,H, MeOH, 25"
8. Ionization Arc<-CO,H, .78 .68 .04 .4 2 35 .06 .95 (I .OO) .07
.38 .26 .9 7
.28 .28 1.01
.28 .84
.oo
0-, rn-, and p-
of set no. 7 for Table 11. reference of set no. 11 for Table 111. 0-, rn-, and p- reference of set no. 10 for Table 111. 0-, rn-, and p- reference for set no. 3 of this table. 0-, rn-, andp- reference of set no. 12 for Table 111. 0-,Kortum, G., W. Vogel, and K. Andrussoco, Pure Appl. Chern., I, 190 (1961). rn- and p , references of set no. 1 for Table 11. 0-, reference for set no. 6 of this table. m-and p , reference of set no. 22 for Table 111. 0-, rn-, and p reference of set no. 21 for Table 111.
0-, rn-, and p- reference
1. 2. 3. 4. 5. 6. 7. 8.
rnP-
.49 .61 .72
0-
rnP
0-
.38 .25 .69
I .oo
1.oo
rnP-
1.oo
.87 .28
3.09
0-
P-
rn-
.01 .42 1.14
4.02 1.48 1.36
0-
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
62
The trans cinnamic acid and phenyl propiolic acid data involve fits of essentially the same precision at a-, m-, and p positions (SD= .05 .02). However, the RMS of these sets is quite low, and consequently, f values of -200 prevail. The interpretation of these results is therefore uncertain. To the extent that the results of Table VII are meaningful, it is of particular interest that KY =p:/pf = .68 for the phenyl propiolic acid, whereas for the trans cinnamic acids, KY = 1.02. These results suggest that in contrast to the ortho substituted benzoic acids, the lines of field forces in the ortho substituted phenyl propiolic acids do (partly at least) penetrate regions of high dielectric solvent. The results for the trans cinnamic acids would then indicate some (but not complete) exclusion of solvent resulting from the presence of the vinyl hydrogens. These interesting results from the application of eq. (1) clearly need to be confirmed by additional studies. ~ values The pi delocalization parameters of Table XXVII show X z p /PI which generally follow the classical sequence hp > hu > Am. There are several exceptions to this trend for A" values, however (sets 1 and 2 of Table XXVII). It is not clear whether these exceptions are significant, or whether they instead merely reflect the difficulty of obtaining ortho data sets which are sufficiently free of incurring proximity effect contributions. The pattern Kf < KF < KY and X p > hu > Am is also clearly shown in the correlation of the proton nmr shifts of substituted phenols in DMSO solution. The 0- and p- substituent effects are best fitted by the parameters (cf. para set no. 24 of Table VI), whereas the rn- substituent effects are best fitted by UR((BA) parameters. The following fitting parameters are obtained from these fits:
*
position
PI
PR
A
KI
SD
f
0-
2.36 1.64 1.45
1.68 .I8
.I1 .47
1.58
1.09
1.63 1.13 1 .oo
.IS .04 .11
.I82 ,056 .I 33
mP-
These correlations are of generally poorer precision than those for reactivity and F-nmr shift data, and in the case of the ortho data set they required rejection of data for the substituents C H 3 C 0 , NOz, and COzR (which give large deviations if included). The latter deviations may be associated with ortho chelation effects. In any case, the K I and h patterns, as noted above, appear essentially as expected. Additional ionization equilibria involving ortho substituents have been reported by Charton (34) to follow eq. (1). The results of our analysis of the data for aqueous ionization of 2-substituted pyridinium ions, o-substituted anilinium ions, and o-substituted phenols are given in Table XXVIII. Comparison with the corresponding meta and para data set results is also included.
W
m
or;
faio;)
0-
mP-
I"(";)
m-
a
"R
3. Ionization Phenols, H,O, 25" 4.06(3.66)b 1.62(1.28)b 2.36 .44 2.48 2.1 8
SD
.17
20
.09(.20)b
.09 20
7
.28 .10 .03
.16 .14
.5 1
4. Partial Rate Factors H-D Exchange Monosubstituted Benzenes, NH,(l) .04 11.52 .48 7 .35 .4 1 7.78 3.22 I .36 7.60 .60 4.55 I .15
.40(.35)b .19 .84
7 18 18
2. Ionization Anilinium Ions, H,O, 25" 5.54 2.76 2.97 1.03 3.09 3.48
.5 0 .35 1.13
n 11 14 13
PR
1. Ionization Pyridinium Ions, H,O, 25" 10.60 1.39 6.02 2.63 5.15 2.69
PI
.I 3 .4 3 .52
A
Fits are indiscriminate; results are obtained with the indicated U R scale Results using the a ~ s c a l e .
mP-
Ia(oR)
OR(BA)
0-
0-
OR
P-
OR
Iaioh)
m-
P-
OR
0-
0 ;
Best fit type
Position
Fitting Results for Other Ionization Equilibria Including the Ortho Position
TABLE XXVIII
.175 .155
.104
.057(.129)b .101 .I 30
.121 .084 .015
.i42 .076 .060
f
S. EHRENSON, R. T. C. BROWNLEE, AND R. W. TAFT
64
While the ortho ionization data are generally fitted with notably poorer precision than for the m- and p positions, there appear t o be characteristic trends indicative of predominant contributions from polar and resonance effects. Thus, for ionization from the ring position (pyridinium ions), XP > Am S ho, whereas for ionization from the side-chain position (anilinium ions and phenols), hp > A" > A". The p I sequence for the former is similar to that for the latter (and for the benzoic acid ionizations of Table XXVII), but the p~ sequence is not. Comparing ionizations from nitrogen, we note
In spite of ionization at a greater distance for the ortho and para positions of the side-chain reaction centers, p~ is greater at these positions for ArNH: than for pyr H". Only at the meta position does p~ reflect ionization at a greater distance in ArNHS than pyr H'. This behavior provides evidence for the much smaller importance of direct quinoidal interaction within the ring than across it: i.e.,
Y'
- X -~
y -_...
+
,
____
- 2 -xQ, x ~
-.a -
In these terms, Shatenshtein's partial rate factors (37) for the H-D exchange of monosubstituted benzenes in liquid ammonia are not anomalous (2m). The analysis of this rate data is included in Table XXVIII. Even though the data are not precise enough to meet the desired standard of precision of fits, the p'; are clearly evident in the results. sequences Ap > Am $=Ao and P:% p;" Consequently, this data set (which is of the u i type) may be taken as providing supporting evidence with the pyridinium ionization (which is of the u i type) for unique h blends for the positions 0- and p - to ionization from the ring position as compared with the X blends for side-chain ionization.
L. Summary A thorough statistical analysis shows that substituent effects (rate, equilibrium, and nmr shifts) in the benzene series cannot be adequately described by either a single or a dual substituent parameter treatment with universal sets of substituent parameters. However, four sets of substituent pi delocalization parameters have been defined utilizing a generalized dual substituent parameter treatment with U I polar effect parameters (eq. 1). These UR parameter sets have been rigorously defended by supporting statistics. Both structural considerations and statistics are shown to support very generally the separation of polar and pi delocalization effects achieved by the use of eq. (1). It is shown, however, that substituent effect sets covering a full compliment of substituent UI and UR properties are critically needed in distinguishing coincidental from significant data fittings by eq. (1).
1. NMe, 2. NH, 3. NHCOMe 4. OMe 5.OC6H, 6. SMe 7. Me 8. C,H5 9. F 10. c1 11.Br 12. I 13. SiMe, 14. MeSO 15. SCF, 16. CF, SO 17. SF, 18. CF, 19. S0,Me 20. CO,R 21. CN 22. NO, 23. MeCO
2
-.83 -1.03 -.79 -.66 .00 -.09 -.32 -.30 -.32 .oo -.01 -.16 -.I7 -.01 .06 .23 .44 .23 .40 .18 -.07 -.lo .49 .70 .73 1.01 1.O1 .54 .81 .72 1.07 .45 .68 I .05 .66 1.29 .78 so .65
1
3a
4a
-.23 -
-.20 -
I .27 1.54
1.82 I .73 1.92
-
-
-
-
-.68 -.25 -.15 -.40 -.03 .31 .61 .68 .63 - .09 1.30 -
-
-1.67 -1.52
-
-
-
-
.9 1 1.14 .67 1.11 1.34
-
-
-
.48
.5 3
so
.26
.35 .56 .60 .59 -
-
-
-.34
-1.05 -1.07 -.21 -.37
-.81
1.10
.22 .38 .38 .38
-.22
-.32
1.18
.25 .39 .4 3 .38
-.21
-.36
(a) Benzoic Acid Type (cf. Tables I1 and 111) Sa 6 7 8 9 10
Data Summary
TABLE XXlX
.82 .96
.17 .30 .37 .36
-.17
-.32
11
.91 1.02
.18 .34 .42 .39
-.18
-.36
12
1.oo 1.17
.23 .42 .47 .45
-.I8
-.32
13
1.14
.21 .39 .43 .45
-.21
-.36
14
1.14
.22 .39 .42 .40
-.19
-.36
15
mw.1 1 Y
d y!
W
I
I
d m ? Y .-.w o
ION
c?
P-9
y!?
e r - 4
I-
N
I
N
?
9
-
r-
1
N
-f
m
I
I
I
z
W
I
I
9 N
I
I
-0
m
I
I
N
w m N 9 I
m
9 I
m
9
c? IO
N
r-
?
0
v
m-m N1" m m
N
NN
I
I
?
m
0
m
d
1 N
-
m
1 3
9?
I
d
c?
mr-
0
N
c?
9 00
-
E:
m
c?
c?
Y
I
m
I
IO
l-
? I
66
rm y!
m
m 09
m "!
W
1
I
m
09
15. SCF, 16.CF,SO 11. SF, 18.CF, 19.S0,Me 20.CO,R 21.CN 22.NO, 23.MeCO
14.MeSO
2.48
.I I
-.46
-.92
-.53 -.56
.lo7 -.60 .096 -.80 .I20
.I52 -1.99 -1.85
4
.42
-.35
-.41 -.23 -.20
.O1
.84 -.27
.40
.013
-.028
.72
.64 .70
.42
.oo
.09 .22 .26 .23
-1.32
7.69 8.10
.34 .45 -2.95 .02 -.19 -2.83 -.52 .49 .99
.34 -2.01
.05 .10
-.I4 -.05
38
.91 -1.19
-.I0
5.0C6H, 6.SMe 7.Me 8. C6H, 9.F 10. c1 1 1 . Br 12.I 13. SiMe,
2.19
-.60
-.I8
-.066
1 . NMe,
35
2.NH, 3.NHCOMe 4.OMe
34 2.34 .5 3
40
-1.26
-3.09 -2.86
42b
-2.33
.36 -.64
1.96 2.49
1.20
.43
.93 - S O
41
-1.02 -2.24 2.85 -2.14 -3.64
-.go
-.I4 .45 .30 -.78
-3.15
39
(a) Benzoic Acid Type (cf. Tables I1 and 111)-conr.
33
37
32
36
30
31
TABLE XXIX-COH~.
m
9 I
“dv)
9999
s
W
u!
I
W
9 I
b,
I
m
9
m m 71
Y
z
m w ?.?
e 9
09
v)
COP-
I
W
I
9
?-.
I
s
vlm 6‘0
I
t-
10
9
t
I
w
9
w m m m
9-11
0,
1
QI
1. NMe, 2. NH, 3. NHCOMe 4. OMe 5.0C6H, 6. SMe 7. Me 8. C,H, 9. F 1o.a 11. Br 12. I 13. SiMe, 14. MeSO 15. SCF, 16. CF,SO 17. SF, 18. CF, 19. S0,Me 20. CO,R 21. CN 22. NO, 23. MeCO
-6.35 -5.90 -8.85 -7.15 -10.25 -10.35 -7.65
-
15.05 14.05 5.15 11.45 7.25 4.50 5.55 2.80 6.40 2.70 2.10 1.35 -.65 -4.80 -
15
18
2.02 -3.29
17
-3.00
-
71.6 40.8
-
-
-14.7 -9.2 -14.2 -20.6 -21.8 -1 1.3 -23.1 -29.0 -25.8
.O
18.4 40.4 34.8 .O -1 7.2 .O -
56.8 48.2 33.1 13.2 12.7 45.3 28.8 30.7 29.4
-
70.7 62.0
-8.95
5.57 2.29 1.83 1.45
4.15
12.84
(b) Sigma Zero Type (cf. Table VIH-cont. 19 20 21 22 23
.21 11.70 1.25 -2.26 -1.60 7.45 4.40 -.82 .20 .63 -.97 5.40 .32 .10 3.00 6.80 .79 -.52 3.10 .9 3 2.60 .98 1.06 1.08 1.70 -SO -3.00 -4.12 -7.50 -5.35 2.72 -5.05 -1.85 -8.00 2.96 2.86 -5.90 3.77 -8.80 4.61 -1.43 -9.01 -2.79 -6.10
15.90 14.40
16
TABLE XXIX-cont.
- 1.44
-.78
-.69
-.23 -.37
.12
.1 I -.23 -.43
.19
.5 3
25
.23
.65
24
-6.0 -4.2
-4.4 -3.0
6.0 3.6
3.9
2.8 4.4 2.0 1.o .4
8.8
11.9
27
8.1
11.8 9.5
26
r-
m
I
I
c! d
W
I
I
t 3
I
d
? I
?
m
r-
I
I
c?
\q
'?
c?
m
m
I
I
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3. NHCOMe 4. OMe 5.OC6H, 6. SMe 7. Me 8. C,H, 9. F 10. c1 11. Br 12. I 13. SiMe, 14. MeSO 15. SCF, 16. CF,SO 17. SF, 18. CF, 19. S0,Me 20. CO,R 21. CN 22. NO, 23. MeCO
2. NH,
-.17
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-.66
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2.20
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-5.51
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2.99 2.73
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-.36 -.40 -.21
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(d) oh Type (cf. Table XII)-conr. 22 23 24 25
TABLE XXIX-conf.
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a Unpublished data sets of A. S. Hoefnagel, M. A. Hoefnagel, R. H. de Vos, and B. M. Wepster. Ionization of Pyridine N-Oxide Conjugate Acids, H,O, 25". Ionization ArCO, H, n-BuOH (cf. reaction 15 of Table 111). Ionization ArCO, H, 73.5% aq. dioxane (cf. reaction 10 of Table 111). Ionization ArCO, H, 43.5%aq. dioxane (cf. reaction 9 of Table 111). Ionization ArCO, H, MeOH (cf. reaction 12 of Table 111). g Ionization ArCH=CHCO, H, H, 0 (cf. reaction 22 of Table 111). H, 35% aq. dioxane (cf. reaction 21 of Table 111). Ionization Arc=-CO, f Ionization &OH, H, 0,25". J Ionization ArOH, 49% aq. CTOH, 22". Rates of methoxide cleavage of ArSiMe,, 50". P-nmr shifts for ortho substituted phenol (OH) in DMSO. Ionization 2-subst. C, H, N@, H, 0, 25". Ionization o-subst. C, H, N q ,H,0, 25". Ionization o-subst. C, H, OH,H, 0, 25". p Ortho log. partial rate factor D substitution in C, H, X,NH, (1). Same as p meta position. r Same as p para position.
78
S. EHRENSON, R T. C. BROWNLEE, AND R. W. TAFT
Evidence is provided by this analysis that (a) structural considerations discriminate among at least four practical classes of pi delocalization behavior, each of which has “limited generality”; (b) the blend of polar and pi delocalization effect contributions to the observed effect of a substituent is widely variable among different reaction or data sets (the contributions may be opposite as well as alike in direction), depending upon structural considerations and the nature of the measurement; (c) solvent may play an important role in determination of the observed blend of effects; (d) it is the first three conditions which lead to the deterioration of the single substituent parameter treatment as a means of general and relatively precise description of observed electronic substituent effects in the benzene series. The potential of eq. (1) in the elucidation of transition-state structure is discussed briefly. Also, a number of additional applications of the method which require further study of the preliminary conclusions or suggestions are pointed out.
Acknowledgment We are greatly indebted to Prof. B. M. Wepster for making available to us his unpublished data (cf. sets 3 , 4 , 5 of Table 11, and sets I , 4 , 5 of Table VIII).
References 1. This work was supported in part by the National Science Foundation (UCI) and the U.S. Atomic Energy Commission (Brookhaven). 2. For previous treatments, cf. the following: (a) Hammett, L. P. Chem. Rev., 17, 125 (1935); (b) Jaff6, H. H., Chem. Rev., 53, 191 (1953); (c) Brown, H. C., and Y.Okamoto, J. Am. Chem. Soc., 79,1913 (1957); (d) McDaniel, D. H., and H. C. Brown, J. Org. Chem., 23, 425 (1958); (e) van Bekkum, H., P. E. Verkade, and B. M. Wepster, Rec. Truv. Chim., 78,815 (1959); (4Taft, R . W., and I. C. Lewis, J. Am. Chem. SOC.,81,5343 (1959); (g) Yukawa, Y., and Y. Tsuno, Bull. Chem. SOC.Japan, 32, 965,971 (1959); (h) Roberts, J. L., and H. H. Jaffk, J. Am. Chem. SOC.,81, 1635 (1959); (i) Taft, R. W., J. Phys. Chem., 64, 1805 (1960); (j) Palm, V., Russ. Chem. Rev., 31, 471 (1961); (k) Wells, P.R., Chem. Rev., 63, 1 7 1 (1963); (1) Ehrenson, S.,Prog. Phys. Org. Chem., 2, 195 (1964); (m)Ritchie,C. D., and W. F. Sager, Bog. Phys. Org. Chem., 2, 323 (1964); (n) Charton, M., J. Am. Chem. SOC., 86, 2033 (1964); (0) Exner, O., Collection Czech. Chem. Commun., 31, 65 (1966); (p) Wells, P. R., S. Ehrenson, and R. W. Taft, Prog. Phys. Org. Chem., 6, 147 (1968); (4)Swain, C.G., and E.C. Lupton, Jr., J. Am. Chem. SOC., 90,4328 (1968); (r) Hammett, L. P., Physical Organic Chemistry, McCraw-Hill, 2nd ed., 1970, Chap. 11. 3. (a) Taft, R. W . , J. Am. Chem. SOC.,79, 1045 (I 957); (b) cf. also references 2(1), p. 244 and 2(p),,p. 19 1 , for background discussions. 4 . Taft, R. W., in N. S . Newman, Steric Effects in Organic Chemistry, Wiley, New York, 1956, Ch. 13; cf. reference (3a), footnote (4), for clarification of symbolism.
SUBSTITUENT EFFECTS IN THE BENZENE SERIES
79
5. cf. references 2(fl and 2(h); E. D. Schmid, et aL, Spectrochim. Acta, 22, 1615, 1621, 1633,1645,1659 (1966). 6. Rakshys, J. W., R. W. Taft, and W. A. Sheppard, J. Am. Chem. Soc., 90, 5236 (1968). 7. (a) References 2(a), 2(c), 2(e), and 2(f); (b) R. W. Taft, S. Ehrenson, I. C. Lewis, and R. E. Glick,J. Am. Chem. SOC.,81, 5352 (1959). 8. The u, values of Table I represent slightly modified values from those given previously. Modifications were based upon examination of more recent data for ionization equilibria involving substituents at saturated carbon: (a) Ionization of XCH,CO,H, H,O, 25", XSF,, Ray, N. H., J. Chem. SOC., 1440 (1963); X=SCF, and CF,SO, Orda, V. V., L. M. Yogupolskii, V. F. Bystrov, and A. U. Stepanyants, J. Gen. Chem., 35, 1631 (1965); (b) Ionization of 4-substituted [ 2.2.2.1 octane-] carboxylic acids, 4-substituted bicyclo [ 2.2.2.1 octa-2-ene-1-carboxylic acids and dibenzobicyclo [ 2.2.2.1 octa2,5-diene-l-carboxylic acids, 50% aq. EtOH, 25", Baker, F. W., R. C. Parish, and L. M. Stock, J. Am. Chem. SOC.,89, 5677 (1967); (c) Ionization of 4-substituted bicyclo [ 2.2.2.1 octane-I-ca~boxylicacids and 4-substituted bicyclo [2.2.1] heptane-1-carboxylic acids in 50% aq. MeOH, 25", Wilcox, C. F., and C. Leung,J. Am. Chem. SOC.,90,336 (1968). 9. Fawcett, F. S., and W. A. Sheppard,J. Am. Chem. SOC.,87, 4341 (1955). 10. Taft, R. W., E. Price, I. R. Fox, I. C. Lewis, K. K. Andersen, and G. T. Davis, J. Am. Chem. SOC.,85, 709, 3146 (1963). 11. Angelelti, J. M., R. T. C. Brownlee, A. R. Katritzky, R. D. Topsom, and L. Yakhontov, J. Am. Chem. SOC.,91,4500 (1969). 12. We are indebted to Dr. Douglas Blagdon for drawing our attention to these data. 13. Tanida, H., Y. Hata, S. Ikegami, and H. Ishitobi, J. Am. Chem. Soc., 89, 2928 (1967). 14. (a) Brownlee, R. T. C., A. R. Katritzky, and R. D. Topsom, J. Am. Chem. SOC.,87, 3261 (1965); (b) Katritzky, A. R., R. F. Pinzelli, M. V. Sinnott, and R. D. Topsom, J. Am. Chem. SOC.,in press. IS. Brown, H. C., and Y. Okamoto, J. Am. Chem. SOC.,80, 4980 (1958). 16. Yukawa, Y., Y. Tsuno, and M. Sawada, Bull. Chem. SOC.Japan, 39, 2274 (1966). 17. (a) Eaborn, C., J. Chem. SOC., 4858 (1956); (b) Dean, E. B., and C. Eaborn, J. Chem. Soc., 2299 (1959); (c) Private communication from Professor Eaborn. 18. Presentation of Professor Y. Yukawa at Second Linear Free Energy Conference, Irvine, California, March 1968. 19. (a) Brownlee, R. T. C., and R. W . Taft, J. Am. Chem. SOC.,90, 6537 (1968); J. Am. Chem. SOC., 92, 7007 (1970); (b) Taft, R. W., N. C. Deno, and P. S. Skell, Ann. Rev. Phys. Chem., 9, 287 (1958). 20. (a) Streitwieser, A., Jr., and H. F. Koch, J. Am. Chem. SOC.,86, 404 (1964); (b) McKeever, L. D., and R. W. Taft,J. Am. Chem. SOC.,88,4544 (1966). 21. (a) Craig, D. P., J. Chem. SOC., 997 (1959); (b) Bordwell, F. G., and P. J. Boutan, J. Am. Chem. SOC., 78, 87 (1956). 22. Taft, R. W.,and J. W. Rakshys, Jr., J. Am. Chem. SOC.,87, 4387 (1965). 23. Pews, R. G., Y. Tsuno, and R. W. Taft,J. Am. Chem. SOC.,89, 2391 (1967). 24. (a) Ramsey, N. F., Php. Rev., 78, 699 (1950); (b) Pople, J. A., and M. Karplus, J. Chem. Phys., 38, 2803 (1963). 25. Exner, O., and J. Jonas, CON.Czech. Chem. Commun., 27, 2296 (1962). 26. (a) Bunnett, 3. F., and E. Zahler, Chem. Revs., 49, 273 (1951); (b) Lewis, E. S., and E. B. Miller, J. Am. Chem. SOC., 75, 429 (1953); (c) Dickson, J. D., and C. Eaborn, J. Chem. SOC., 3036 (1959). These authors first point out that the rates of aqueous
80
27. 28. 29. 30. 31. 32. 33. 34.
35. 36.
37.
S. EHRENSON, R. T.C. BROWNLEE, AND R. W. TAFT decomposition of p and m-substituted phenyldiazonium salts could be described by an equation of the form of eq. (1). Gutbezahl, B., and E. Grunwald, J. Am. Chem. SOC.,75, 559 (1953). cf., however, reference 20. Holtz, D.,Prog. Phys. Org. Chem., 8, 55 (1971). Nelson, J. H., R. G. Harvey, and R. D. Ragsdale,J. HeFero. Chem., 4, 591 (1967). Eaborn, C., H. L. Hornfeld, and D. R. M. Walton, J. Chem. SOC.(B), 1036 (1967). Latta, B. M., and R. W. Taft, J. Am. Chem. SOC.,89, 5172 (1967). Kirkwood, J. G., and F. H. Westheimer, J. Chem. Phys., 6 , 5 0 6 , 5 13 (1938). Charton, M., Prog. Phys. Org. Chem., 8, 235 (1971) has reported extensively on correlations of rate data for ortho substituted benzene derivatives using the dual substituent parameter treatment in the form with an additional (intercept) parameter, and in our opinion, too limited substituent data sets. For these and related reasons which we have discussed, we question the significance of many of Charton’s correlations. M. Charton has summarized his earlier correlations of these data in reference 35. Our results are dissimilar to those of Charton for the reasons indicated. (a) Charton, M., and B. I. Charton, J. Org. Chem., 33, 3872 (1968); (b) Bowden, K., N. B. Chapman, and J. Shorter,J. Chem. SOC.,5239 (1963); (c) Bowden, K., M. Hardy, and D. C. Parkin, Can. J. Chem., 46, 2929 (1968). Shatenshtein, A. I.,Adv. Phys. Org. Chem., I , 155 (1963).
Substituent Effects in Nonaromatic Unsaturated Systems By Marvin Charton Department of Chemistry. Pratt Institute. Brooklyn. New York 11205
CONTENTS
I . Introduction . . . . . . . . . . . . . . . . . . I1. Substituents on Carbon-Carbon Double Bonds . . . . . . .
A . Substituted Vinyl Sets . . . . . . . . . 1. DipoleMoments . . . . . . . . . 2. Ionization Potentials . . . . . . . . B . VinylideneSets . . . . . . . . . . . 1. Equilibria . . . . . . . . . . . 2 . Reaction Rates . . . . . . . . . . 3 . Physical Properties . . . . . . . . . c. trans-Vinylene Sets . . . . . . . . . 1. Equilibria . . . . . . . . . . . 2. Reaction Rates . . . . . . . . . . 3. Physical Properties . . . . . . . . . D . cis-Vinylene Sets . . . . . . . . . . 1. Equilibria . . . . . . . . . . . 2 . Reaction Rates . . . . . . . . . . 3 . Physical Properties . . . . . . . . . E. Reactions of Carboncarbon Double Bonds . . . 1. Charge Transfer Complexes . . . . . . 2. Addition Reactions . . . . . . . . . a. Electrophilic Addition . . . . . . . b . Nucleophilic Addition . . . . . . . c . Radical Addition . . . . . . . . d . Carbene Addition . . . . . . . . e. Diels-Alder Cycloaddition . . . . . . f . 1,3.Dipolar Cycloaddition . . . . . . I11. SubstituentsonCarbon-Heteroatom DoubleBonds . A . Substituted Heterovinyl Sets . . . . . . . B. Heterovinylidene Sets . . . . . . . . . C. Heterovinylene Setswith Heteroatom Reactionsites D . trans-Heterovinylene Sets . . . . . . . . E . cis-Heterovinylene Sets . . . . . . . . . F . Amidines and Carboxylic Acids . . . . . . 1. Amidines . . . . . . . . . . . . 2. Carboxylic Acids . . . . . . . . . . . . . . . . . . . a. Equilibria b . Reaction Rates . . . . . . . . . 81
. . . . . . .
. . . . . . .
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. . . . . . . . . . . . . . . . . . . . .
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.
. . . . . . . . . .
. .
. . .
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. . . . . . . . . . . . . . . . . . . . . . . .
82 86 86 86 90 90 90 93 93 94 94 94 97 97 99 105 106 107 108 108 108 120 121 126 126 132 132 133 135 137 144 146 146 146 146 149 151
82
MARVIN CHARTON
IV . Substituents on Carbon-Carbon Triple Bonds . . . . . . . . A . Substituted Acetylene Sets . . . . . . . . . . . . B Ethynylene Sets . . . . . . . . . . . . . . . . 1. Properties of the Ethynyl Proton . . . . . . . . . . 2. Other Ethynylene Sets . . . . . . . . . . . . . C. Reactions of Carbon-Carbon Triple Bonds . . . . . . . . V . Substituentson Carbon-HeteroatomTripleBonds . . . . . . . A. Substituted Nitriles . . . . . . . . . . . . . . . B . Heteroethynylene Sets . . . . . . . . . . . . . . VI . Substituents on Cyclopropane Rings . . . . . . . . . . . A. Substituted Cyclopropane Sets . . . . . . . . . . . B . Cyclopropylidene Sets . . . . . . . . . . . . . . C. trans-Cyclopropylene Sets . . . . . . . . . . . . . D. cis-Cyclopropylene Sets . . . . . . . . . . . . . E. Reactions of Cyclopropane Rings . . . . . . . . . . . VII . Substituents on Heterocyclopropane Rings . . . . . . . . . A. Substituted Heterocyclopropyl Sets . . . . . . . . . . B . Heterocyclopropylidene Sets . . . . . . . . . . . . C. Heterocyclopropylene Sets . . . . . . . . . . . . . D . Heterocyclopropanes with Heteroatom Reaction Sites . . . . . VIII Substituents on Other Unsaturated Systems . . . . . . . . . . . . . . . . . . . . . . . . . . A . Pyridones B . Quinones . . . . . . . . . . . . . . . . . . C. Multiple Substitution at Nonequivalent Sites . . . . . . . D. Conjugated Dienes and Polyenes . . . . . . . . . . . E . Allenes and Cumulenes . . . . . . . . . . . . . . IX . Conclusions . . . . . . . . . . . . . . . . . . A . Transmission of the Electrical Effect . . . . . . . . . . B . Composition of the Electrical Effect . . . . . . . . . . C. Other Conclusions . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . Appendix 1. Substituent Constants from Sources Other than Reference 23 and Reference 29 . . . . . . . . . . . . . . Appendix 2 . Data Used in Correlations . . . . . . . . . . . .
.
.
. .
. . . . .
. . . . .
. .
. .
. .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . .
. . . . . . . .
. .
. . . .
.
. .
. .
151 151 154 154 156 156 156 157 157 160 160 163 163 164 164 164 164 164 164 165 166 166 166
173 174 175 175 175 181 181 182 189 192
I . INTRODUCTION Linear free energy relationships (1-9) have been of great utility in the quantitative study of reactivity and of physical properties as a function of structure . In the study of carbon compounds. attention was first directed to mand p-substituted benzene sets (1.2.4) . The application of linear free energy relationships to compounds bearing the substitutent on an sp3 hybridized carbon atom has been reviewed (3) . Reviews have appeared on the application of the Hammett equation to ortho-substituted benzenes (10). naphthalenes (1 1). and heteroarenes (12) . No systematic review of the application of linear free energy relationships to nonaromatic unsaturated systems has appeared as yet. although these compounds comprise a large fraction of the known organic
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
83
compounds. It is the objective of this work to provide a critical survey of this field. The first mention in the literature of the application of the Hammett equation to a nonaromatic unsaturated system seems to be a private communication from Carter to Evans and DeHeer (13) reporting a linear relationship between the Hammett up constants and the Eo values of substituted quinones. No details were given. Jaffi (2) had suggested that rigid molecules might be treated by means of the Hammett equation. In accord with the proposal, Harnsberger, Cochran, and Szmant (14) attempted the extension of the Hammett equation to pKa data for X'X2C=NNH2, where X was methyl, phenyl, or substituted phenyl. The first clear-cut example of the application of the Hammett equation to nonaromatic unsaturated systems is the work of Charton and Meislich (15), who reported the correlation of pKa data for trans-3substituted acrylic acids, trans-3-substituted-2-methylacrylic acids, and trans-3substituted-2-carboxyacrylic acids with the Hammett equation by means of the up constants. This work was followed by that of Hine and Bailey (16, 17), who reported a correlation of the rates of reaction of trans-3-substituted acrylic acids with diphenyldiazornethane by means of the up constants. This effort was followed by a report by Charton (18) that pKa data for substituted acetylenic acids were correlated by the up constants. Charton (19) has also reported correlations of data for substituted cyclopropanes and substituted cyclopropane carboxylic acids with the Hammett equation. Since 1964, a number of other papers have appeared demonstrating the applicability of both the simple Hammett equation
Qx =pox + h
(1)
and the extended Hammett equation
Q = ~ U I , X+P%,x + h
(2)
to various sets of data for nonaromatic unsaturated systems. Of the two equations, the extended Hammett equation, first proposed by Taft and Lewis (20),is the more widely useful, because it accommodates the complete range of substituent effect composition. The simple Hammett equation can be adapted to substituent effect composition only in a crude manner by the proper choice of substituent constant. To clarify this point, we must consider what is meant by the composition of the electrical effect. Taft (21) has suggested that the electrical effect of a substituent is composed of localized (inductive and/or field) aqd delocalized (resonance) factors. Thus we may write the substituent constant of the group X as OX = hUI,X
&uR,X
(3)
MARVIN CHARTON
84
We had previously described the composition of the electrical effect by means of E , where
E = SIX
(4)
Substitution of eq. (3) into eq. (1) gives
equivalent to eq. (2) with a = pX, 0 = pS. Then
E = PIa We believe that a more useful measure of the composition of the electrical effect may be defined as
where
PR
is the percent resonance effect. Furthermore,
The quantities E and PR are related to each other by the expression
E . 100 pR=E+1
(9)
Values of pR for the substituent constants commonly used with eq. (1) are given in Table I. When correlations are made with eq. (l), the substituent constant used determines the composition of the electrical effect.
TABLE I Composition of the Electrical Effect in Substituent Constants Substituent Constants "I am 0 ;
"P "P
"P "R
PR
0 25 40
50 62 60 100
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
85
As the extended Hammett equation is capable of accommodating the complete range of electrical effect composition, it will be used in this work. The question then arises of what substituent constants to choose for the localized and delocalized effects. Recently, Swain and Lupton (22) have proposed a new separation of electrical effects into localized and delocalized factors. Although they have proposed new localized effect substituent constants, they agree with most other workers in the field that the UI constants are a valid measure of the localized effect. They have, however, proposed a new set of delocalized (resonance) effect parameters, and they have suggested that the UR values are not pure resonance effect parameters. In our opinion, the Swain-Lupton treatment is invalid for the following reasons: (a) The separation proposed by Swain and Lupton depends upon values of u, and up for Me3" which are reported by McDaniel and Brown (23). These authors have reported probable errors of +.2 for these substituent constants. It seems to us that parameters based on values so much in doubt are of little use. (b) The separation of Swain and Lupton is based on the assumption that the trimethylammonio group is independent of resonance interaction: that is, the resonance effect of this substituent is zero. The trimethylammonio group is isoelectronic with the tertiary butyl group, which has been firmly established as an electron donor by resonance. We would therefore expect that the trimethylammonio group should also be an electron donor by resonance. In accord with this expectation, a value of ut of -.15 obtained from infrared spectra of para-disubstituted benzenes has been reported for the trimethylammonio group by English, Katritzky, Tidwell, and Topsom (24). This result is supported by values of -.11 for U R obtained from pKa measurements (25) and of -.08 for ug obtained from "F-nmr data for p-fluorotrimethylanilinium chloride (26). A value of -.12 for OR can be calculated from pKa values of substituted phenols (24,27). These results are in value determined for the trimethylammonio group (4). agreement with the Additional support for an electron don& delocalized effect by the trimethylammonio group comes from the observation of the effect of NR; groups on benzenoid chemical shifts (28). It was suggested that the results indicate a somewhat higher electron density at the position para to the NR', group than at the meta position. In view of the above arguments, we have continued to use the substituent constants as a delocalized effect parameter. Correlations in this paper have been made therefore with 01 and OR constants. The UI values were generally taken from the compilation of Charton (29), and UR values were obtained from the equation OR = Op-UI (10)
ui
where use was made of the up values reported by McDaniel and Brown (23). Other substituent constants used will be reported in Appendix 1. The correlations were carried out by means of multiple linear regression analysis (30).
86
MARVIN CHARTON
11. SUBSTITUENTS ON CARBON-CARBON DOUBLE BONDS
Foremost among the classes of the nonaromatic unsaturated systems is that of compounds in w h c h the substituent is bonded to a carbon-carbon double bond. It is convenient to divide the data sets for carbon-carbon double bonds into five categories: vinyl, vinylidene, trans-vinylene, cis-vinylene, and reactions of carbon-carbon double-bond sets.
A. Substituted Vinyl Sets Certain physical properties of substituted ethylenes may be correlated with the extended Hammett equation. Included in this category are dipole moments and ionization potentials.
1 . Dipole Moments The first recorded correlation of dipole moments with substituent constants was observed by Taft (3), who reported results for alkyl cyanides, chlorides, iodides, and tertiary amines. Kross and Fassel (31) have reported the correlations of dipole moments for 4-substituted nitrobenzenes with the simple Hammett equation. Rao, Wohl, and Williams (32) have studied the correlation of dipole moments of &substituted benzenes with eq. (1) and of monosubstituted benzenes with the equation PX = Pb,,xl
(1 1)
Van Beek (33) proposed the equation
C)
log - =pox for the correlation of dipole moments. This equation has been criticized by Exner (34), who points out that it fails for px = 0. Exner has himself proposed the equation -+---+
PX = P I ~ I , X U I , X+ P R ~ R , x % , x *+Po
(13)
for the correlation of dipole moments. In this relationship, 4 is the distance between charges due to the inductive (localized) effect and dR the distance between charges due to “polar conjugation”; ug signifies the use of u& for electron donor substituents and u< for electron acceptor substituents. This equation is based on the resolution of p into localized (PA) and delocalized ( p s ) components, a concept inherent in the mesomeric moments defined by Sutton (35) as (14) &n = pArX - PAlkX
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
87
Sharp and Walker (36) have reported “good linear plots” of px - p~ for 3- and 4-substituted pyridines, pyridine-N-oxides and nitrobenzenes against the appropriate substituent constants. Charton (37) has reported correlations of dipole moments for substituted ethylenes and related compounds with eq. (1) using the UI, urn and up constants. Best results were generally obtained with up. Only those substituents which are symmetric with respect to the substituent-to-carbon bond are included in the sets studied. In this manner, the problem of the conformation of the substrate was avoided. All of the sets studied may be written in the form XGZ, where X is the substituent, Z is a constant substituent, and G is the skeletal group to which Xpand Z are bonded (in this case, the carbon-carbon double bond). For the trans-vinylene sets, members of the set for which up,x> up,z were considered positive, whereas members for which up,x < up,z were considered negative. For the vinylidene sets, members of the set for which luP,xl> luP,zl were considered to have the sign of uP,x, whereas members of the set for which luP,xl < luP,zl were considered to have the same sign as that of up,z. The quantity which is really of interest in the correlation of sets bearing a constant Z substituent is the moment of the X group, px. This quantity is given by the expression pX
= p Z - Ebbs
(15)
where k b s is the observed dipole moment and pz the group moment of the constant Z substituent, which is equal to the moment of the compound ViZ. Applying eq. (2) to eq. (15) and solving for Ebbs gives Ebbs
= - c r ~ ~ X - P ~ R , X - h + ( l l ~ I , Z + P ~ R+, hZ
(16)
or as Z is constaot, /Jobs = a‘U1,X +P’OR,X
+h’
(17)
equivalent to eq. (2). Thus, correlations have been carried out directly with observed dipole moments through use of eq. (2). The quantity of interest in the case of the vinylidene sets is again px. From the law of cosines, we obtain px = -pz
COS
8 f d & b S - SinZ8 p i .
(18)
For vinylidene sets, 8 is approximately 120°, and p X = 0 . 5 pz *d/&s-O.75p&.
(19)
For Z with small values of pz@z < S), pX zEbbs
As for the vinylidene sets studied here, pz is small. These correlations were carried out with the Ebbs values. The sets studied are given in Table 11. Results of the correlations are set forth in Table 111.
MARVIN CHARTON
88
TABLE I1 Vinyl Sets ~
Q
Set 2-1 2-2 2-3 24 2-5 26 2-1 2-8 2-9 2-10 2-1 1 a
Substrate
Substituted ethylenes trans-2-Substituted styrenes trans-3-Substitutedpropenes Ir 2-Substituted-1-bromoethylenes Ir 2-Substituted-1-chloroethylenes P 3-Substituted acrylonitriles P 2-Substituted propenes Ir 1-Substituted styrenes Ir 2-Substituted 1,3-butadienes Substituted ethylenes I trans-3-Substitutedpropenes Dipole moment. Ionization potential. Ira
Ir
’fh
Reference 31 31 31 31 31 31 31 31 31 41 41
The significance of r is <90% CL unless otherwise noted. The confidence levels for the significance of regression are reported as superscripts on F values. Confidence levels for the significance of a,0, and h are reported as superscripts on the values of s,, sp, and Sh. Of the nine sets correlated with eq. (2), seven gave significant correlations. The other two sets each had only four members. Undoubtedly, had more data been available, significant results would have been obtained for ali sets. The composition of the electrical effect in these sets is reported in the form of the pR values in Table IV. Most of the sets studied show a value of pR of 42, which corresponds roughly to that of the up” substituent constants. It has been shown (38) that for correlations with the simple Hammett equation (eq. 1) of sets having a constant substituent Z, PZ = P l 2 u Z + P H (20) where pz is the value of p for the set bearing the constant substituent, PH is the value for the set which bears n o constant substituent (the set for which the constant substituent Z = H) and p l z is the coefficient of the interaction term (39). In the case of the extended Hammett equation [eq. (2)], the equations analogous to eq. (20) are
The results obtained for the correlation of a and 0 values of sets 2-1 through 2-4 are not significant. Thus, eqs. (21) and (22) are not obeyed in the case of dipole moment data.
4.64 4.62 5.58 5.07 6.21 3.75 1.27 1.32 .6 11 .769
5.50
4.70 6.06
LY
3.34 4.68 3.93 3.33 3.31 6.13 3.55 4.72 1.13 1.66 2.51 2.29 1.70
P
7.O7tlg 42.08e 4.611' 45.95'
11
99.5%CL. 99.0% CL. 98.0% CL. 97.5%CL.
d
.36Se .982g .786g .370g 1.30rn .472e .997rn .120g .491g .273e .38On .112'
.550e
SLY
80.0% CL. 50.0%CL. O 20.0% CL. p <20.0% CL. Number of points in set.
*rn <90%CL.
90.0%CL.
' 95.0%.CL.
.038
.057
.482 .267 .613 .260 .0975 .398 .293 .233 .0378 .452 .218 .194 .0554
.I25 ,013 .314 .781. .891J .788 ,328 319 ,823 .051 .156
40.48e 176.2e 16.139 29.32' 196.9e 41.75' 58.78f 34.19'
.949 .993 .930 .975 .996 .994 .983 .993 .9995 .674 .936 .869 .989
.0930 .0473 .414 -1.29 -1.39 -3.80 .344 .198 -.0309 9.75 9.85 9.46 9.33
d
Sest
re
Fb
Ra
h
a Multiple correlation coefficient. F test for significance of regression. Partial correlation coefficient of 01 on OR. Standard errors of the estimate, a,p, and h. 99.9% confidence level (CL).
2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-10A 2-11 2-11A
Set
TABLE III Results of Correlations with Vinyl Sets
3.92" .717g 2.39". .196J .580h .361e .861k .266'
.fillJ
.863g .521e 1.48J 2.1Sg,
spd
.227' ,166' .376" 2.15" .060Se .387k .184m .223' ,0287" .160e .0922e .Ille .0387e
sg
7 4 5 20 15 6 5
4
12 8 8 6 6
nq
MARVIN CHARTON
90
TABLE IV Composition of the Electrical Effect-Vinyl Sets Set
PR
Set
pR
Set
PR
Set
PR
2-1 2-2 2-3
42 44 42
2-4 2-5 2-6
42
2-1
'
2-10A 2-llA
66 69
a
2-8 2-9
23
In this set, 01 = f(UR). Correlation for this set was not significant.
2. Ionization Potentials
A number of correlations of ionization potentials for substituted benzenes (40-42), benzyl (43), phenoxy (44), and alkyl (45) radicals and substituted pyridines (46)with the simple Hammett equation have been reported. Charton (47) has studied the application of the extended Hammett equation to substituted ethylenes and carbonyl compounds. The sets studied here are reported in Table I1 (sets 2-10 and 2-1 1). Results of the correlations are set forth in Table 111. The results obtained are much improved by the exclusion of the values for X = Cz H3, Ac, F, H and OAc from set 2-10 (set 2-10A) and the value for X = H from set 2-11 (set 2-11A). The composition of the electrical effect corresponds to that found for the ui constants as is shown by the PR values reported in Table IV. B. Vinylidene Sets We have classified the available vinylidene sets into three categories: equilibria, rates, and physical properties. 1 . Equilibria
Charton (48) has examined the correlation of pKa values for 2-substituted acrylic acids with the Hammett equation. This work was extended by Sandris (49). Data exist for nine sets of 2-substituted acrylic acids. In eight of these sets, the substrate bears constant substituents. These data have been correlated with eq. (2): the sets studied are set forth in Table V. The results of the correlations are reported in Table VI. Seven of the nine sets studied gave significant correlations, and only two of these sets gave significant values of 0. Unfortunately, of those sets which gave significant correlation with eq. (2), only set 5-1 contains an electron acceptor substituent. Thus, with regard to the composition of the electrical effect, only the pR value of set 1 is meaningful.
”
a
5-5 5-6 5-1 5-8 5-9 5-10 5-11 5-12 5-13 5-14 5-15 5-16 5-17 5-18 5-19 5-20 5-21 5-22
54 ”
I,
91
trans
,.
,,
,,
1,
”
7,
11
9,
2-Substituted acrylic acids a-Substituted-cis-cinnamic acids
Substrate
trans-1-Substituted-2-chloroethylenes ” 1 ” 2-bromoethylenes ” 2’ ” styrenes ” 1 ” propenes ” 1 ” ” 3 ” methylacrylates ” 1 ” lbutene-3-ones
MeAc 2 : 3 EtOH-H2O
H,O
H2O 50% V/V EtOH-H2O
50% V/V EtOH-H20
H2O
Solvent
Parameters for the calculation of chemical shift in nmr spectra. Chemical shifts in nmr spectra. Frequencies, nmr spectra.
SH 6H
YC
6H 6H
6H 6~ 6H
VC
6H
”
a ” ” crotonic ” 2 ” -3,34imethylacrylic acids kr 2 ” ally1 chlorides 103kr 2 ” vinyldielthylphosphates 2; Substituted ethylenes
’
pKa
5-1
5 -2
5-3
Q
Set
Vinylidene Sets
TABLE V
KI H,Ot
Reagent
20 85
51 56 56
56 56 56
56
55 56
53
48 48 50 49 48 50 49 48 51 51 52 54
25 25 25 25 25 25 25 25
25
Ref.
T“C
h)
W
5-6 5-7 5-8 5-9 5-10 5-11 5-12 5-13 5-14 5-15 5-16 5-17 5-18 5-19 5-20 5-21 5-22
5-5
5-1 5-2 5-3 54
Set
P h
a
For footnotes, see Table 111.
-4.14 -.873 4.31 -3.39 1.89 3.90 -2.22 3.03 5.36 -3.00 1.53 5.06 -4.25 -2.92 4.47 -3.81 -1.22 5.77 -3.85 -1.40 5.60 -3.55 -.925 4.66 -3.56 2.16 4.72 -.845 -1.23 -.656 3.31 -7.82 -.0518 ,583 1.24 -.166 -.189 1.38k -.417 43.4 -78.1 338.0 .421 -1.08 -.487 .814 -.920 -.527 -1.01 .789 -.833 -.663 -.278 -.933 -1.27 -.312 -.lo7 -21.4 119. -203. -1.01 1.37 -1.40 8.48 -4.15 -.707
a
.994 ,974 .992 .991 .966 .9995 .998 .999 ,924 .968 317 ,489 .601 .716 .458 ,615 .615 .321 .559 .932 .697 .992
Ra 174.0e, 27.34' 31.351 56.60' 28.06' 527.3' 288.4: 262.2' 5.858' 7.511' 1.005' 3.142k 1.414' 3.148' .798' .609' .6 10' ,460' 1.823' 3.322' 2.362' 30.19'
Fb
.256 ,781 .859 .778 .760k .859 .778 329 ,792 .859 .785 .214 .215 .014 .198 ,174 .lo5 ,250 ,250 .177 .039 .773
rc
d
sa
sb
:234e .353k .144 .283 ,855' 2.33" .814h 2.08h ,203 .166 .519' 1.38" .643g 1.07k ,248 .0511 .206' ,525" .0735 .229' .610m .0591 .251j ,566" .449 1.42m 3.88O .0624 .251m .640" .648 3.49'. 5.60" .408 .494' .332O .473 .74gp .877m 21.4 42.9" 34.2k .590 .853" 1.31' 1.02O 1.76O ,448 .452 1.04" 1.85O ,550 ,793" 1.13p SO2 .724m 1.03' 11.7 24.4' 46.9" .690" .821m .383 .125 .65Sk 1.09k
d Sest
Results of Correlations with Vinylidene Sets
TABLE VI
.353k .234e .202' .144e .15ge .05 1og .063Se .0467g .311g .0622' .582' .168g .300" 18.3e .336" .282" .289m .307h .281° 12.9' .224g .113m
d Sh
11 11 4 8 4
5
9 5
9
7 4 5 4 5 4 4 23 8
5
7 6 4
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
93
Values of pR are given in Table VII. The mi value obtained for set 5-1 seems to show that the substituent effect in the vinylidene position is predominantly a localized effect. Further data are necessary to firmly establish the composition of the electrical effect. TABLE VII Composition of the Electrical Effect-Vinylidene Sets Set
pR
Set
pR
Set
5-1 5-2 5-3 5-4 5-5
17
5-6 5-7 5-8 5-9 5-10
a
5-11 5-12 5-13 5-14 5-15
a a
41
a
a
pR
a
Set
5-16 5-17 5-18 5-19 5-20
pR
Set
pR
5-21 5-22
b
a p was not significant for this set.
Correlation was not significant for this set.
2. Reaction Rates Only two sets of rate data are available for vinylidene substitution, and each set is minimal, consisting of only four points. It is not surprising then that significant correlations were not obtained for these sets. The problem of vinylidene rate data has received very little attention. Further investigation in this area would be very welcome. 3. Physical Properties The only physical property which has been studied for substituted vinylidene sets is the nmr chemical shift of the vinylidene proton in substituted ethylenes and in frans-l,2-disubstituted ethylenes. The first attfmpt at correlating chemical shift data for substituted ethylenes with the Hammett equation appears to be the work of Banwell and Sheppard (53), who reported a correlation of A, values with the CJRconstants, the A2 values being defined by the equation
where 6 ~ 6, ~ and , 6~ are the chemical shifts of the vinylidene, trans-vinylene, and cis-vinylene protons respectively. Eleven sets of chemical shift data were correlated with eq. (2). The sets studied are shown in Table V, and the results of the correlations are reported in Table VI. Only in one set were the results significant (set 5-12), and even in this set, correlation was very poor. It seems certain that no meaningful relationship
94
MARVIN CHARTON
exists between substituent constants and the chemical shifts of vinylidene protons. Unfortunately, no data are extant on any other physical property of vinylidene compounds, such as infrared spectra. This area is again one which would repay investigation.
C. trans-Vinylene Sets We shall again classify the available data into the categories of equilibria, rates, and physical properties. 1. Equilibria The work of Charton and Meislich (15) has already been referred to. Hogeveen (58) has reported a correlation of pKa values for trans-3-substituted acrylic acids. Hogeveen (50) and Sandris (49) have studied the pKa values of p-substituted cinnamic acids. Bowden (59) has also studied pKa values of trans-3-substituted acrylic acids. Data for 10 sets of pK values have been correlated with eq. (2). The sets studied are set forth in Table VIII: the results of the correlations are given in Table IX. Of the ten sets studied, eight gave significant results. Particularly important is the excellent correlation obtained for the trans-3-substituted acrylic acids in water. This large set (16 members) includes a wide range of substituent type. The composition of the electrical effect, as indicated by the values of pR reported in Table X, is 48%. This value is comparable to the composition of the electrical effect in the ionization of 4-substituted benzoic acids. The value of pR for the sets bearing constant substituents will be expected to differ somewhat from this value if eqs.(21) and (22) are obeyed. The sets available are insufficient to test eqs. (21) and (22) by correlation. It would be interesting to study an extensive series of pKa values for trans-3-substituted acrylic acids in various solvents to determine whether pR is independent of the medium, as is the case for the 4-substituted benzoic acids. 2. Reaction Rates
As was noted previously, Hine and Bailey (16, 17) have obtained correlation of rate data for the reaction of trans-3-substituted acrylic acids and diphenyldiazomethane with the Hammett equation. Bowden has reported correlation of rate data for the reaction of trans-3-substituted acrylic acids with diphenyldiazomethane (59) and the alkaline hydrolysis of trans-3-substituted methyl acrylates (69) with the Hammett equation. Sufficient data are available for nine sets of rate studies. The sets studied are reported in Table VIII. The results of the correlations are given in Table IX. Of the nine sets studied, seven gave
8-11 8-12 8-13 8-14 8-15 8-16 8-17 8-18 8-19 8-20 8-21 8-22 8-23
8-3 84 8-5 8-6 8-7 8-8 8-9 8-10
8-1 8-2
Set
a
”
P
”
”
” ”
”
methacrylic cis-crotonic ,,
9,
”
”
7,
”
”
..
”
”
4 ” vinylacetic ” 3 ” l-aza-[2,2,2] -bicycle2-octenes ” 3 ” ethylacrylates ” 3 ” ” ” 3 ” acrylicacids ” 3 ” ” ” ” 3 ” ” ” ” 3 ” ” ” ” 3 ” ” ” ” 1 ” 3chloropropenes ” 1 ” 3 ” 1 ” methylacrylates Substituted ethylenes
”
P
”
>> 39
”
P
”
$
”
”
”
”
3 3
t-BuOH EtOAc EtOH 50%EtOH-H,O CCl,
EtOH
OHOHMeOH Ph,CN,
25 18.8 35 30 30 30 30 25 25
25 25 25 25 25 25 25 25
25 25
55
70 69 69 16 59 59 59 71 71 69 54 53
50,58,62 60 63-6 50 50 49 62,64,67 68
59,60 61
Reagent T”C Ref.
Chemical shifts. Frequencies, nmr spectra.
70% v/v dioxane-H,O MeOH EtOH
50% v/v EtOH-H,O
HZO
HZO 80% Methyl cellosolve-H,O 50%v/v EtOH-H,O
tmns-3-Substituted acrylic acids ,, ” 3 ” 7.
Solvent
Substrate
Infrared spectra frequencies. Parameters for the calculation of chemical shift in nmr spectra.
Q
trans-Vinylene Sets
TABLE VIII
8-6 8-7 8-8 8-9 8-10 8-11 8-12 8-13 8-14 8-15 8-16 8-17 8-18 8-19 8-20 8-2 1 8-22 8-23
8-5
a
-2.26 -2.59 -1.44 -2.58 -2.84 -2.94 -3.44 -2.95 -1.18
8-1 8-2 8-3 8-4
P 4.35 6.65 5.22 4.63 4.56 4.10 5.37 5.3 1 4.33 11.02 -1.14 1.43 1.11 .00757 .0808 -.364 -.691 .438 .793 1735. .0556 -.0416 339.
h
For footnotes. see Table 111.
-2.09 -3.34 -4.27 -2.65 -3.43 -4.09 -4.90 -3.76. -1.47 -5.75 2.33 4.88 2.83 3.85 3.59 .22O -.954 1.16 1.63 1.62 1.60 2.18 2.09 3.03 2.97 -5.19 -8.80 -7.81 -14.5 15.9 48.9 .892 2.11 -1.35 -3.38 51.8 188.
a
Set .997 .9995 .962 .991 .994 .851 .997 .970 .982 .998 .9997 .986 ,857 .973 .998 .992 .994 .637 .559 .977 .874 .873 .829
Ra 1148e 485.9 24.60g 83.20f 172.9e 2.632' 96.1 gk 16.OOk 40.31g 261.5: 841.7' 51.66f 5.512k 36.10f 462.3e. 64.30: 79.23' .341' .228' 31.34g 32.49e. 8.00lJ 6.607'
Fb
.017 .065 .5 39 .038 .324 .896 .859 .7 78 .525 .657 .116 .374 .122 .205 .122 .778 .778 .819 .819 .374 .214 .215 .014
rc
.0553 .0442 .262 ,116 .0896 .291 .0717 .185 .0498 .lo2 .0391° .187 .I78 .138 .0452 .0694 .0894 1.50 2.71 2.28 .361 .470 33.1
.058l: .O12OJ .52d .245g .159e 1.51m .288k .5 78' .131g .30lg .l08' .394g .288' .230g .0730e .216h .27gg 6.41' 11.6' 4.81' .437k .744m 66.3"
d SLY
d Sest
Results of Correlations with trans-Vinylene Sets
TABLE IX
Sh
.0762e .0190e .159' .0227g 1.09h .178e .0706e .377g .318e .0515e 3.39" .245g .736k .O71Sg 1.54m .160e .276h .036Se .763k .0789e .178' .0209h .137g .508g .3540 .129g .367' .088p .0326k .0897e .0599' .576k .0773h .742' 15.4O 1.43p 27.8O 2.59p 1.66e 6.19g .148O .294e .872h .298p 52.8h 28.3e
$
4 6 7 7 7 5 5 4 4 6 23 8 9
5
4 5 6
5
16 4 7 6 7
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
97
TABLE X Composition of the Electrical Effect-trans-Vinylene Sets Set ~
pR
Set
48 56 75 51 55
8-8 8-9 8-10 8-11 8-12 8-13 8-14
pR
Set
pR
Set
pR
8-15 8-16 8-17 8-18 8-19 8-20 8-21
50 51 51
8-22 8-23
78
~~
8-1 8-2 8-3 8-4 8-5 8-6 8-7
a
59
55
63 52 42
a a
75 70
CQrrelation was not significant for this set. p was not significant for this set. a and p differ in sign: therefore, correlation was not significant. (Y was not significant for this set. a
significant correlations. The two sets which did not give meaningful results involve the solvolysis of trans-1 -substituted-3-chloropropenes.As the solvolysis of benzyl chlorides is frequently not correlated by the Hammett equation, these results are certainly not surprising. The value of pR for these data in general is about 50,as is shown by the values in Table X. It is interesting t o note that the value of pR observed for the reaction of the trans-3-substituted acrylic acids with diphenyldiazomethane in EtOH, t-BuOH, and EtOAc is independent of the solvent, according to Bowden’s data. The comparatively high value of pR for the alkaline hydrolysis of the trans-3-substituted ethyl acrylates probably results from the small size of the set (four points). The composition of the electrical effect is in general comparable to that of the analogous 4-substituted benzene sets. 3. Physical Properties The infrared absorption frequencies of trans-3-substituted methyl acrylates gave a significant correlation with eq. (2). The value of pR obtained is 75, which indicates predominance of the resonance effect. Three sets of nmr chemical shifts also were studied. All three sets gave significant correlation with eq. ( 2 ) . The values of pR obtained in two of the three sets were 70 and 78. Again, the resonance effect appears to-predominate.
D. cis-Vinylene Sets There is an obvious structural analogy between cis-vinylene sets, 1 , and ortho-substituted benzene sets, 2. The possible existence of proximity effects in
MARVIN CHARTON
98
a: 2
1
ortho-substituted benzenes was proposed long ago and continues to be of interest (10). Such proximity effects can also conceivably exist in cis-vinylene sets. According to Charton (lo), the proximity effect can be pictured in terms of three possible major factors: (a) electrical effects; (b) steric effects; (c) intramolecular secondary bonding. As proximity electrical effects are a function of the UI and OR constants, and secondary bonding interactions when present may be a function of the uI constants; the effect of an ortho- or a cis-vinylene substituent may be represented by an equation including electrical and steric terms. The presence or absence of a steric effect may be ascertained in the following manner (72). There are four major cases of interest. (a) The steric effect obeys a linear free energy relationship. Then we may write the equation QX=CWOI,X+@R,X
+
$Vx + h
(24)
where u is the steric parameter. We may define u by the equation
ux
5
rv,x - r V , H = rv,x - 1.20
(25)
where rv,x is the Van der Wads radius of the X group and W,H is the Van der Wads radius of the H atom. Values of ux are reported in Table XI. (b) The steric effect does not obey a linear free energy relationship. Then for any given member of the set, we may write
QX=W,X+POR,X+S[ + h (26) where SX is the steric effect of the substituent. (c) The steric effect is constant. Then Qx = ~
, + @xR , x + ~ ’
(27)
where h‘ = h + Sx. (d) The steric effect is negligible or nonexistent. Then
% =aoI,X ‘@R,X+h
(2)
The data to be examined are correlated with eq. (24). Successful correlation with eq. (24) is a necessary but not sufficient condition for the existence of case (a). Strong evidence for case (a) is provided by a confidence level of J, greater than or equal to 90.0. The confidence level of J, is obtained by means of a “student t” test of J,. If J, is not significant, then this fact implies either the existence of cases (b), (c), or (d), or the use of an incorrect steric parameter. The data are now correlated with eq. (2). If the correlations with
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
99
TABLE XI Values of v
X
U
F NO2 t-Bu H
.27 .35 1.24
0 a
X CI O=C-Za OZ C,H,
u
.55
SO .32 .57
x
Br Ph NZ'Z' S0,Z
u
x
U
.65 .57 .35 .99
I Me SZ Me$
.78 .52 .60 1.40
X CN CH,Z CF,
v
.40 .52 .91
z i s any atom or group of atoms.
eq. (24) and (2) are both unsuccessful, either case (a) exists and the choice of steric parameter is incorrect, or case (b) exists. Although it is impossible to distinguish between these alternatives at the present time, the second is the more likely. If the data give significant correlation with eq: (2), then cases (a) and (b) may be excluded, as in those cases the data must include a variable steric term which is not accounted for by eq. (2). Then a nonsignificant value of $ obtained in a correlation with eq. (24) coupled with a successful correlation with eq. (2) indicates the existence of case (c) or case (d). A comparison of the experimentally observed values of h (that data point for which X = H) with the calculated value of h obtained from the correlation serves to distinguish case (c) from case (d). In case (c), h&s st halowhereas in case (d), hobs = hCde Once again, the data have been divided into three categories: equilibria, rates, and physical properties. 1. Equilibria Ionization constants of cis-3-substituted acrylic acids have been correlated with the Hammett equation by Hogeveen (58) and by Charton (60). Charton has correlated ionization constants for a number of other cis-vinylene sets with the Hammett equation (60). Charton and Charton have correlated some cis-vinylene sets with the extended Hammett equation [eq. (2)] (73). Sufficient data are available for twelve sets of cis-vinylene equilibria, of which four sets represent ionization constants of hydroxy compounds (sets 12-1 to 12-4) and eight sets represent ionization constants of carboxylic acids (sets 12-5 to 12-12). All sets have been correlated with eq. (24) and eq. (2). Sets studied are reported in Table XI. Results of the correlations are reported in Table XIII. Sets designated A were correlated with eq. (24), sets designated B were correlated with eq. (2). In the case of the second ionization constant of 2,3,5,6-tetrahydroxy-l,4benzoquinone (set 12-3), it is uncertain which hydroxyl group ionizes: therefore, the value for X = OH was excluded from the correlation. All of the sets 12-1 to 12-4 gave significant correlations with both eq. (24) and eq. (2),
12-1 12-2 12-3 124 12-5 12-6 12-7 12-8 12-9 12-10 12-11 12-12 12-13 12-14 12-15 12-16
Set
Q
1’
I.
Solvent
I,
a-Substituted tetronic acids H Z 0 3,6-Disubstituted-2,5dihydroxy-l,4-benzoquinones 3,6” 2,5 ” 1,4 3-Substituted-2-hydroxy-1,4-naphthoquinones cis-3-Substituted acrylic acids ,, ” 3 ” 50% v/v EtOH-H,O ” 3 ” methacrylic ” H*O trons-3Chloro-cis-3-substituted acrylic acids p-Substituted trans cinnamic acids p” 50% V/V EtOH-H,O pp” ” crotonic ” H2O cis-3-Substituted acrylic acids MeOH ” 3 ” methylacrylates 70% v/v dioxane-H,O ” 3 ” acrylicacids EtOH ,, ” 3 ” t-BuOH
Substrate
cis-Vinylene Sets
TABLE XI1
”
MeOH OHPh,CN,
25 25 25 26-33 25 25 25 25 25 25 25 25 35 18.8 30 30
Reagent T“C
60 60 60 60 59,60 58 60 60 60,74 50 49 60 69 69 59 59
Ref.
12-17 12-18 12-19 12-20 12-21 12-22 12-23 12-24 12-25 12-26 12-27 12-28 12-29 12-30
d ” ”
3 1
”
”
methylacrylates -1-butene-3-ones
propenes
2-Substituted-l,4-naphthoquinones
” ”
”
’I
1 1
rruns-1 -Substituted-2-bromoethylenes ” 1 ” 2-chloroethylenes ” 2 ” styrenes
1,
,, 3 ” 3 ” methyl acrylates Substituted ethylenes
”
”
a ir spectra frequencies. Parameters for the calculation of chemical shifts in nmr spectra. Chemical shifts. Frequencies, nmr s p e c ~ a .
vd
6 6
6 6 6
6 6
5
va Zb
kr
THF
cc1,
EtOAc ”
”
30 30
80
59 69 54 53 55 56 56 56 56 56 57 56 56
TABLE Results of Correlations ~
Set
12-1A 12-1B 12-2A 12-2B 12-3A 12-3B 12-4A 12-4B 12-5A 12-5B 12-6A 12-6B 12-7A 12-7B 12-8B 12-9A 12-9B 12-10B 12-llA 12-llB 12-12A 12-12B 12-13A 12-13B 12-14A 12-14B 12-15A 12-15B 12-16A 12-16B 12-17A 12-17B 12-18A 12-18B 12-19A 12-19B 12-20A 12-20B 12-21A 12-21B 12-22A 12-22B 12-23A 12-23B
&
-3.51 -3.71 -8.22 -7.83 -8.41 -7.72 -5.67 -3.23 -2.28 -2.41 -1.08 -1.85 -3.75 -1.80 -1.03 -2.12 -2.25 -3.02 -3.23 -3.34 -3.14 -3.14 .0325 -.405 2.81 2.30 1.98 1.90 2.37 2.30 3.30 3.21 30.5 28.2 1.06 1.22 -.775 -1.02 31.7 78.5 -1.14 - 1.26 -1.72 -1.92
P
tL
-2.16 -1.71 -6.37 -6.48 -4.82 -5.04 -3.99 -6.30 -1.71 -1.56 -4.94 -4.62 -5.16 3.11 -3.44 -.929 -.463 -2.13 -3.74 -3.20 -2.67 -2.55 -.403 1.83 1.90 4.53 1.97 2.37 2.41 2.81 3.52 3.98 12.4 24.6 2.14 2.21 -2.86 -2.89 170. 169. -1.65 -1.41 -3.71 -3.38
-.739 .608 1.10 .952 -.274 -.588 -2.01 -.313
-.345 -.0625 -1.43 - 1.68
-.253 -.250 -.295 -7.81 .520 -1.17 73.4 -.476 -.362
102
h
RB
.967 3.93 .960 3.63 .998 2.78 2.82 .997 5.18 .9996 .994 5.26 .9991 4.01 .995 4.12 .987 4.22 .981 4.12 .990 5.42 .983 5.33 .982 4.66 .939 4.54 .960 3.43 .910 4.46 .900 4.39 ,994 5.76 5.55 .998 .992 5.48 4.70 .996 4.69 .996 1.29 .983 1.oo .661 .99996 1.61 1.27 .734 .114 .987 .0621 .976 .988 -.358 - .409 .981 -.648 .992 -.708 .986 1.000 1735. .962 1733. -.0476 .913 .906 .171 ,915 .269 ,850 -.148 .968 311. .905 327. .0762 3 9 5 -.0972 .879 -1.15 .962 -1.25 ,955
Fb
33.28e 46.61e 178.2g 285.2e 4 105.5' 89.21' 381.1f 138.3f 48.40f 64.02e 16.741 29.19' 9.167' 7.4501 5.903' 1.596' 4.284' 40.57' 93.92k 64.16' 82.43f 178.2e 9.435' .777' 3917.' 1.166' 13.04' 20.24j 13.65: 25.0d 19.951 35.94' 143.ak 12.56k 3 1.60e 45.81e 6.903k 6.525' 24.94f 13.64g. 6.677' 10.23' 4.111' 10.2gk
-
XI11 with cis-Vinylene Sets
.198 ,198 ,085
.252 .395 ,631 .154
.085
.163 .163 .786 .786 .385 .385 .493 .493 .800
.639 .281 .275 .295 .520 .431 .819 .241 .297 .760
300
.773 .737 .737 .859 .778 .778 .762 .762 .778 ,778 .778 .778 .778 .778 .778 .778 .778 .7¶8 .778 .778 .214 .214 .215 .215 .014 ,014 .199 .199 ,105 .lo5
.629 .665 .656 .710 .562 .691 .656 .710 .656 .710 .656 .710 .656
.710
,656 .710 .656 .710 .354 .272 .237 .022 .481 .015 .230 .375 .524 .485
.323 ,331 .257 .249 .117 .307 .0717 .145 .lo6 .112 .271 .249 248 .322 .256 .420 ,311 .126 ,0769 .113 .0941 .0784 .148 .424 .00928 .483 .110 .lo7 .130 .117 .149 .136 .556 2.21 .327 .330 .371 .441 13.9 21.5 .272 .265 .320 ,246
.446e .427e .66S9 .489e .313' .637g .884! .9 18' .222e .213e 1.11' .571k 1.59" 1.24" 1.34' 1.51h 1.07" 508m ,247' .354h .251h .209e .474p 1.32' .0298g 1.51" .352m ,333' .417m .364' .480k .423h 1.78' 6.91k .4 17h .399g .613" .697" 31.8" 43.2" .418' .383h .880: .568 103
.791! .718' .426g .397e .263' .670h .838' .864g .396h .401h 1.20m 1.oa' 5.89' 3.15" 2.24" 3.93p ' 2.69" 1.30" .704" .941k ,854k .620' 1.3SP 3.52' .0849j 4.01" 1.oo" .885" 1.19" .968" 1.37" 1.13k 5.09" 18.4" .273e .269e .699h .817h 22.2e 34.49 .67Sk S90k 1.52" l.Olk
.614" ,676" .309" .297k .2 16" ,705' 1.30"
1.01p .189" .22op .363" .022gg .269' .319' .367'
.55se
1.36"
"
.44 1
.695" 24.d s79" .848'
.28Se .149e .253g .241g .117h .302g .071Se .12Se .0992e .061ee .258' .218g .248' .3079 .231j .41gk .263g .126h .076gg .097ge .0939e .065ge .148k .367" .00926g .41gk .109" .0910° .130" .lOlk .149m .117' 1.91e .229* .136" .343" .279O 13.0e 18.4e .262' .1510 .320" .157h
11 11
6 6 5 5 6 6 8 8 5 5 5
5 4 5 5 4 5 5 6 6 5 5 5 5 5 5 5 5 5 5 5 5 23 23 8 8 9 9 9 9 5 5
104
MARVIN CHARTON TABLE
12-24A -1.64 12-24B -1.72 12-25A -.982 12-25B -1.08 12-26A -1.30 12-26B -1.47 12-27B -50.9 12-28A -1.14 12-28B -1.30 12-29B -2.60 12-30A -47.7 12-30B, -65.9 12-30B2 -95.3
-3.57 -3.45 -2.54 -2.38 -2.89 -2.62 -40.5 -1.40 -1.30 .808 -104. -105. -121.
-.200 -.391 -.655
-.339
-46.2
-.968 -1.03 -1.31 -1.46 -.337 -.585 -224. -.624 -.740 -.860 -405. -420. -423.
a Multiple correlation coefficient. F test for significance of regression. Partial correlation coefficients of uI on OR,01 on u Standard errors of the estimate, a,0, J / ,and h.
, q
.9998 .997 .937 .930 .945 .932 .985 .929 .919 .954 .926 .888 .967
900.8i 162.4g 16.80f 25.7Se 19.41e 26.27e 16.89' 8.424' 13.56g 5.082' 12.12g 13.03f 43.59e
on v .
99.9% confidence level (CL). 99.5%CL. 99.0%CL. 98.0%CL. i 97.5% CL. j 95.0%CL. 90.0%CL.
although generally better results were obtained with eq. (2). The value of J/ was not significant in sets 12-1 to 12-3, however, and was barely significant in set 12-4. As values of hobs are in fairly good agreement with values of hCdc,,we may exclude case (c). As cases (a) and (b) are excluded by the success of the correlation with eq. (2), we conclude that case (d) prevails: that is, there is no significant steric effect in these sets, Of sets 12-5 to 12-12, only six were large enough to correlate with eq. (24) [it is necessary to have at least five numbers in a set which is to be correlated with eq. (24)] . Of these six sets (sets 12-5 to 12-7, 12-9, 12-11, 12-12), three gave significant correlation with eq. (24). None of these sets (12-5, 12-11, 12-12) gave significant values of J / .Of the eight sets correlated with eq. (2), four gave significant results. Of the remaining sets, two had only four points [minimal sets for correlation with eq. (2)] and two had five points (sets 12-8, 12-10, 12-6, and 12-9, respectively). No conclusions are possible for those sets which did not correlate with either eq. (24) or eq. (2). In the case of the other sets, we can immediately exclude cases (a) and (b). The
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
105
XIII-cont.
.I74 ,174 ,250 .250 .250 .250 .177 .039 .039 ,773 ,073 ,073 .189
.423 .392 .243 .293 .243
.293
S 1 7 .245
3 6 9 .013
,0207 ,0595 ,224 ,220 250 .260 4.90 .I94 .185 .211 14.6 16.6 9.86
.050gh .135g .344' .318B .384h .374g 10.2m .416k .333h 1.11" 28Sm 29.9k 19Sg
.0870h .234g .498' .453,
.0507m
3 5 9
S14"
s34g 19.6" .437J .397J 1.86O 19Sg 22.1g 13.8e
"
.46 1
,455" 26.7m
.0206h .0375g .215, .123e .239" .145g 5.38h. .192' .108g .192m 13.1e 10.6e 6.33e
5 5 11 11 11 11 4 8 8 4 10 10 9
e 0 . m CL. 80.0% CL. " 50.0%CL. O 2O.O%CL. <2O.O%CL. Number of points in set. Correlation is not significant because of difference in sign between 01 and p. Significance of r is <90% CL unless otherwise noted. Confidence levels for significance of regression are reported as superscripts on F values. Confidence levels for significance of a,p, $, and h are reported as superscripts on values of s,, sp, s$, and sh.
*
values of hobs are in reasonably good agreement with the values of hcdc. We may therefore conclude that these sets (12-5, 12-6, 12-11, 12-12) are examples of case (d). With regard to the composition of the electrical effects, values of pR for the sets studied are reported in Table XIV. The sets in which the hydroxyl group is the reaction site generally exhibit a pR value of about 39. The cis-3-substituted acrylic acids show a pR value of 39 in aqueous solution. The value of 71 obtained in 50% aqueous ethanol seems too large. 2. Reaction Rates Bowden has studied the application of the Hammett equation to the kinetics of the reaction of cis-3-substituted acrylic acids with diphenyldiazom'ethane (59) and with methanol (69) and the rates of alkaline hydrolysis of cis-3-substituted methyl acrylates (69). The sets studied are reported in Table XII. Results of the
MARVIN CHARTON
106
TABLE XIV Composition of the Electrical Effect-cis-Vinylene S Sets Set
pRa
Set
pR
12-11 12-12 12-13 12-14 12-15 12-16 12-17 12-18 12-19 12-20
49 $5
Set
PR
~~~
12-1 12-2 12-3 12-4 12-5 12-6 12-7 12-8 12-9 12-10
32 45 39 66 39
”
55
54
12-21 12-22 53 12-23 64 12-24 67 69 12-25 12-26 12-27 j0 12-28 12-29 12-30 56e
6b4
a Values of pR were obtained from correlations with eq. (2). Correlation was not significant for this set. p was not significant for this set. a was not significant for this set. pR was calculated from set 1 1-30B2.
correlations with eq. (24) and eq. (2) are given in Table XIII. The acid-catalyzed rates of esterification of the cis-3-substituted acrylic acids (set 12-13 ) did not give significant correlation with either eq. (24) or eq. (2). In contrast, the acid-catalyzed esterification of 2-substituted benzoic acids is correlated by eq. (2) with the resonance effect predominant (75). The base-catalyzed hydrolysis of cis-3-substituted methyl acrylates (set 12-14) is correlated by eq. (24) but not by eq. (2), and $ is significant, suggesting the existence of case (a). Again, this behavior is in contrast to that of the 2-substituted methyl and ethyl benzoates, which correlate best with eq. (2) and show a predominance of the localized effect (76). As sets 12-13 and 12-14 are small, it would be useful to reinvestigate these reactions with more extensive data and in other solvents. The three sets of rate data for the reaction of cis-3-substituted acrylic acids with diphenyldiazomethane all give significant correlations with eq. (2) but not with eq. (24). This fact excludes cases (a) and (b). As the values of hcdc and hobs are not significantly different, the data must belong to case (d): that is, there is no meaningful steric effect. 3. Physical Properties Chemical shifts of cis protons in substituted ethylenes and in trans-1,2disubstituted ethylenes have been correlated with the Hammett equation in
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 107
several instances (77-79, 54). Crecely, Crecely, and Goldstein (80) have correlated chemical shifts of cis protons in 2-substituted naphthoquinones with the up constants. Data for twelve sets of nmr chemical shifts of cis protons are extant. The sets studied are given in Table XII; results of the correlations with eq. (24) and eq. (2) are set forth in Table XIII. Eight of the ten sets correlated with eq. (24) gave significant results. Of the 12 sets correlated with eq. (2), 10 gave significant results. The ten sets which did not give significant results with eq. (2) had only four members each. It must be noted that best results for correlation of set 12-30 with eq. (2) are obtained by the exclusion of the value for X = OAc (set 12-30B2 in Table XIII). In general, better correlation was obtained with eq. (2) than with eq. (24). Of the eight sets which gave significant correlation with eq. (24), seven did not have meaningful values of $ . It would seem then that we can exclude cases (a) and (b). The values of hcdc are not significantly different from the values of hobs : therefore, case (c) may be excluded, and the data generally belong to case (d). That is, there is no steric effect. The composition of the electrical effect in the case of nmr chemical shifts for substituted ethylenes is indicated by the value of pR of 53 for set 12-22. The results for sets 12-20 and 12-21 suggest, however, that this value may be too low (a was not significant for these sets). The composition of the electrical effect in the case of the trans-1,Zdisubstituted ethylenes bearing a constant substituent will depend on whether or not their 01 and 0 values obey eqs.(21) and (22). Niwa (56) has suggested that in correlations of these data with the Hammett equation, the p values obtained obey eq. (20). Correlation of 01 with eq. (21) did not give significant results, whereas correlations of 0 with eq. (22) did give significant results. The rrans-l,2-disubstituted ethylenes show an average p~ value of 62. The values of p~ for the sets studied are set forth in Table XIV. The carbonyl stretching frequencies in the ir spectra of cis-3-substituted methyl acrylates (set 12-18) were also correlated with eq. (24) and eq. (2). Barely significant correlations were obtained with both equations. The value of I ) obtained in the correlation with eq.(24) was not significant. We may therefore probably exclude cases (a) and (b). As the hcdc is not significantly different from hobs, we may exclude case (c). This set is therefore probably an example of case (d): that is, there is no meaningful steric effect. No conclusion can be made with regard to the composition of the electrical effect in this set, as 0 was not significant in the correlation with eq. (2). In conclusion, it would seem that most sets of cis-vinylene data are free of steric effects.
E. Reactions of Carbon-Carbon Double Bonds Among the most important reactions of olefinic compounds are those involving the carbon-carbon double bond. It is convenient to divide phenomena occurring
108
MARVIN CHARTON
at carbon-carbon double bonds into formation of charge transfer complexes and addition reactions. 1. Charge Transfer Complexes
The ability of compounds with double bonds to act both as electron donors and as electron acceptors in charge transfer complex formation is well known (81, 82). Hammond (83) has studied the correlations of association constants and of the energy of the charge transfer absorption of 2-substituted-l,4benzoquinones complexed with hexamethylbenzene with the Hammett equation. Charton (84) has studied the correlation with eq. (2) of association constants of 1-substituted propenes with Ag' . Sufficient data are extant for three sets of charge transfer complex association constants and one set of charge transfer absorption energies. The sets studied are reported in Table XV. Results of the correlations with eq. (2) are given in Table XVI. All the sets studied gave significant results. An improvement in the correlation for set 15-2 occurs on the exclusion of the values for X = Ac and X = C 0 2Me (set 15-2BA). The composition of the electrical effect in the case of the 1,4-benzoquinones seems to depend upon the degree of substitution. The association constants and charge transfer absorption energies of the 2-substituted-l,4-benzoquinone-hexamethylbenzene complexes (sets 15-2 and 15-4) show values of pR of 55 and 44 respectively. Values of pR are set forth in Table XVII. 2. Addition Reactions Perhaps the most characteristic property of the carbon-carbon double bond is its ability readily t o undergo addition reactions with a wide range of reagent types. It will be useful to consider addition reactions in terms of several categories: (a) electrophilic additions; (b) nucleophilic additions; (c) radical additions; (d) carbene additions; (e) Diels-Alder cycloadditions and (f) 1,3-dipolar additions. a. Electrophilic addition. The correlation of rates of addition of chlorine to 3,3-disubstituted acrylic acids with the Hammett equation using the constants was reported by de la Mare (86). Dubois and co-workers have correlated rates of bromination of substituted ethylenes and multiply substituted ethylenes with the Taft modification of the Hammett equation (87,88, 89, 90). Dubois and Bienvenue-Goetz (90) have also considered the use of the equation
ui
Q x = p * C ~ z+6Z&,x + h
where the
(28)
& values are the steric parameters of Taft. Dubois and co-workers
5:
,,
H2O
aq. HCIO, CF,CO,H H2O
,,
AcOH AcOH MeOH AcOH, HBr
15-21 15-22 15-23 15-24
rruns-2'-Substituted styrenes 2-Substituted propenes , " 2 Substituted ethylenes
'?
?runs-l,2-Disubstituted elthylenes " 1,2 Substituted ethylenes trans-2'-Substituted styrenes Substituted ethylenes
trun~-2'-Substitutedstyrenes Substituted ethylenes
4-benzoquinones 2-Substituted- 1,4-benzoquinones Substituted ethylenes AcOH AcOH-H~O AcOH aq. HCIO,
H*0 cc1,
1-Substituted propenes " -1,4-benzoquinones 2-
2,3,5,6-Tetrasubstituted-l,
Solvent
Substrate
THF
Q
15-20
15-4 15-5 15-6 15-7 15-8 15-9 15-10 15-11 15-12 15-13 15-14 15-15 15-16 15-17 15-18 15-19
15-1 15-2 15-3
Set
CarbonCarbon Double-Bond Sets
TABLE XV
diglycine anion glycine anion c-aminocaproic acid anion DL-alanine anion
Reagent
Ref.
0
108 108 108 108
100
24 25 25 25 25 24 24 25 24 24 38 25 25
30 30 30 30
83 94 95 94 96 96 96 96 94 94 87,91 94 94 97 98 99
25 24
25 84 25 83 18-20 85,83
T"C
+.
15-25 15-26 15-27 15-28 15-29 15-30 15-31 15-32 15-33 15-34 15-35 15-36 15-37 15-38 15-39 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 15-50 15-51 15-52 15-53 15-54 15-55 15-56
Set
Q
1-Substituted-2-methylpropenes 1 ” 2 2 ” propenes
2-Substituted propenes Substituted ethylenes
nuns-1,2-Disubstituted ethylenes ” 1,l” ” Substituted ethylenes
Substituted ethylenes
1,l-Disubstituted ethylenes
” propenes 2 Substituted ethylenes
Substrate
I9
0
THF
.,
3,
,,
,,
,,
9,
9.
,.
,,
9,
,I
9.
gas phase
isooctane
isooctane gas phase
,,
9,
vinyl acetate radical methyl methacrylate radical methyl acrylate radical dichlorocarbene
Cl,H*, so styrene radical
9.
Br,
F,No
Pho
CCl, cyclopropyl radical
CFO,
CFO,
Eta
0 -78 -78
60
60 60 60 60
78 100 118 40 80 120
65 65
138 139 139 139 139 139 140 140 140
137
Meo
isooctane
,, ,,
110 109 109 109 111,123,124 111,123,124 125 126 130 130 131 131 132 133 133 134 135,136 135,136 135,136 137 137 137
24 0 30 45 65 65 60 100 65 180 65 65
OMeMorpholine
MeOH
gas phase
Ref.
T“C
Reagent
Solvent
Table XV-(continued)
c.
15-57 15-58 15-59 15-60 15-61 15-62 15-63 15-64 15-65 15-66 15-67 15-68 15-69 15-70 15-71 15-72 15-73 15-74 15-75 15-76 15-77 15-78 15-79 15-80 15-81 15-82 15-83 15-84 15-85 15-86 15-87 15-88 15-89 15-90 15-91 15-92 ”
trans-l,2-Disubstituted ethylenes ” 1,2
trans-3-Substituted alkyl acrylates 2-Substituted alkyl acrylates Substituted ehtylenes
trans-3-Substituted ethyl acrylates Substituted ethylenes
”
1,3-butadienes ” 1,3 ” 1 ” 1,3 ” 2,3 ” 1,3 ” 2,3 ” 1,3 ” 2 ” 1,3 ” 2‘ ” 1,3 ” 2 ” 1,3 ” 2 ” 1,3 ” trans-l,2-Disubstituted ethylenes cis 1,2 trans 1,2 cis 1,2 trans 1,2 cis 1,2 trans-3-Substituted methyl acrylates ” 3 ” acrylonitriles ” 1,2-Disubstituted ethylenes cis 1,2 ” 1,l Substituted ethylenes
2 2 2,3
Me, NCHO PhMe
CHCl, Et, 0 PhH
CCI,
Dioxane
PhH
,I
THF PhH, AlCI, ,,
>,.
dioxane
PhH
,
91
diphenyldiazomethane N-methyl€-phenylnitrone
picryl azide benzonitrile oxide diphenylnitrile imine
I.
phenyl azide
9,l Odimethylanthracene cinnamaldehyde isoprene pentachlorocyclopentadiene
2,3dimethylbutadiene
9,lO dimethylanthracene
cyclopentadiene
te tracyanoethylene methyl acrylate
maleic anhydride
80 80 80 40 120 85 120
20
25 25 25
-18 25 25 30 30 roomT 20 20 20 20 40 40 20 20 130 130 130 130 130 130 130 170
140 142 142 142 142 142 143 143 143 143 142 142 142 142 142 142 142 142 142 142 142 142 142 144 144 146 147 148 146 146,148 149 149 150 151 151 151
-3.60 1.23 1.15 2.27 -.693 -9.72 -13.5 -7.14 -6.22 -22.4 -19.1 -10.7 -8.35 -13.0 -9.76 .328 -7.49 -3.72 -4.32 -8.48 -18.3 -1.26 1.79 1.90
15-1 15-2B1 15-2B2 15-3 15-4 15-5 15-6 15-7B, 15-7B2 15-8 ,Y 15-9 h, 15-10 15-11 15-12 15-13 15-14 15-15 15-16 15-17 15-18 15-19 15-20 15-21A 15-218 15-21C 15-22A 15-22B
1.70 ,995
a
Set
-5.21 .942 1.39 -.310 -.540 -5.60 -3.38 -3.02 -4.77 2.29 332 -5.82 -2.73 -3.56 -4.53 -13.2 2.20 6.80 -32.9 -13.7 -.554 -3.88 19.2 4.31 23.5 19.4 8.14
P .794 -.266 -.0952 -.244 -.540 2.28 .912 3.41 2.94 6.10 4.86 4.70 3.32 2.25 2.37 1.64 1.93 2.01 -.158 ,672 .835 .444 -1.45 -1.17 -1.09 -.940 -1.58
h
.987 .862 .96 1 .986 2.98 .980 .965 .881 .928 .974 .964 .857 .837 .981 .931 .973 .990 -990 .959 .985 .995 .948 .797 .678 .699 .921 348
Ra
8.437k 2.568'
38.93' 11.58' 36.67e 35.07' .971 49.28' 40.82e, 8.672' 12.45: 28.15: 19.98' 2.762l 2.337' 78.65e 3.238' 44.79e 48.46i 48.64i 22.96' 16.46l 262.7e 22.04' .873' ,424'
Fb
.376 ,193
.976' .028 .094 .778 .215 .244 .378 .012 .121 .838k .838k .376 .376 .133 .178 .477 .330 .512 .447 379 .694 ,428 ,319 .418
rc
.286 ,236 .146 .144 .0665 .369 .696 .756 .603 .974 1.01 1.94 1.43 .440 1.09 .569 .228 .187 .65 1 ,375 .187 ,192 ,758 .924 .635 .495 .773
d Sest
d
Sff
1.61" 2.49'
3.18" .33gg .21lr: .449J .0882e 1.35' 1.5Se 1.79h 1.50h 5.231 5.43J 6.85" 5.05" 1.04e 3.93" 1.3SP .895h .423h 3.46" 1.8grn 1.12e .492k 2.81' 3.58O
Results of Correlations with CarbonCarbon Double-Bond Sets
TABLE XVI
6.41' .311h .230e .120p .066 le 1.15' 3.71" 2.39" 2.1Ok 10.5p 10.9p 5.54" 4.08O 1.75k 4.63O 1.61e 1.03rn .81fjh 6.08' 2.41rn 1.93O .875' 2.14' 9.33O 17.0". 4.76' 3.59rn
1.05" 1.98O
.124m .0367e .60 1 .397" .7819 .667h .886' .920h 3.33" 2.45" .23ge 1.15" .292' .239h ,201' .587p .375" ,1749 .0990g 2.14O 3.15O
.loo"
.143rn
d Sh
5
4 4 4 6
8 5 5 7 4 8 8
5 5 9 4
7 6 6
9 8
5 11 9 5 11 7
nq
15-22C 15-23A 15-23B 15-23C 15-24A 15-24B 15-24C 15-25A4, 15-25A2 15-25B 15-25C1 15-25C2 15-26Al 15-26A2 15-26B 15-26Cl 15-26C2 15-27A, 15-27A2 15-27B 15-27C1 15-27C2 15-28A, 15-28A2 15-28B 15-28C1 15-28C2 15-29-1 15-29-2 15-30-1 15-30-2 15-31-1
.923 1.93 3.13 3.05 2.54
-1.95 ,817 -.434
-1.30 2.33 1.71
-1.74 2.30 2.21
-1.39 2.27 .895
2.25 2.71
2.38 2.54
17.5 17.8 3.63 23.6 20.2 9.26 17.1 8.76 18.1 7.53 10.1 14.4 19.9 35.0 7.94 22.0 31.6 19.4 32.9 7.13 20.8 29.6 14.7 25.1 5.77 16.9 23.9 3.16 3.32 .699 1.05 2.44 ,0124
-2.13 .831 - 2.6 2 -1.49 .138 -1.26 2.08 -.554 .365 1.04 -.0758 2.30 1.79 1.66 1.66 1.08
-.555
-.140 -.0337 -1.45 -2.81 -.211 -.0538 -3.13 -3.35 -.804 -1.62 .375 -3.47 -2.60
-.5 14
.891 ,794 .698 .643 ,911 .865 ,877 .654 .976 .951 .610 .918 599 374 ,882 .590 .862 .628 .892 .877 .622 ,877 ,689 .944 .918 .667 .941 .751 .944 .956 .954 .755 3.870k 16.44' 10.49k 5.074' 3.969k
2.718' 20.52f 5.345'
1.9571 9.699' 3.337'
1.401' 6.489k 3.505'
.746' 9.869' 5.431'
4.862' 1.49 1'
.855' ,476'
.205 .173 .786 324 .208
,435 .528 ,280
.435 .528 .280
.453 ,540 .280
,327 S82 .426
.538 .465
,319 ,418
,501 ,834 .983 .744 .632 1.02 .60 1 .934 ,340 .450 .799 .435 1.76 1.09 1.14 1.62 1.02 1.42 .841 1.06 1.33 .820 1.oo ,464 .707 .957 .435 .725 .408 .384 .541 .768 1.26" .757k 1.18m 1.85" 1.36m .
3.28' 1.62' 2.97p
4.64' 2.95" 4.43'
5.80° 3.85' 4.80'
3.16' 1.51" 1.83'
2.66" 4.63'
3.10' 3.80'
.448h 23.5' 9.93' 1.99" 6.16k 5.41" 5.42k 9.39" 4.23m 2.38m 7.59" 4.39k 15.0: 10.6J 3.02m 12.3m 8.30h 11.8m 8.04' 2.78m 9.90k 6.61g 8.33m 4.41g 1.86k 7.14' 3.50e 1.28' .720g 3.02m 5.52p 1.46m .396g .260g .307J .433m .44 1
1.98" 1.07' 1.6lP
2.81' 1.95" 2.41'
3SIp 2.53" 2.6 I"
2.06p 1.11" 1.57"
1.63" 3.35'
2.35p 3.36*
4 9
5
9 8 9 7
5
9 8 9 8
5
8 7 9 8
5
4 8 7
5
4 4
5 5
4
5
6 4 4 4
15-31-2 15-32-1 15-32-2 15-33-1 15-33-2 15-34-1 15-34-2 15-35-1 15-35-2 15-36-1 15-36-2 15-37-1 e 'i; 15-37-2 15-38 15-39 15-40 1541 1542 1543 15-44-1 15-44-2 15-45-1 1545-2 1546-1 1546-2 1547-1 15-47-2 1548-1 15-48-2
Set
-.0898 2.11 1.35 .0727 -1.93 -1.70 -1.06 -2.47 -5.00 -2.28 -4.44 -1.41 -3.47 -4.79 -12.1 -.128 -.487
-.850
3.13 1.42 2.43 -.470 -.282 -.173 -.0570 -1.19 -1.35 -1.53 -1.72
3 '
2.5 1 1.96 1.43 2.58 2.04 1.93 1.73 .701 -.0338 .783 -.799 -8.18 -3.39 3.07 2.33 .212 -5.78 -4.93 -4.55 2.19 -8.26 1.98 -6.92 2.43 -4.94 4.71 -25.4 -.929 -1.52
P .782 1.80 1.19 2.44 2.05 1.78 1.60 2.47 2.20 2.4 1 2.09 -.411 -.5 13 1.35 1.37 1.08 ,916 1.51 1.91 .950 .0506 .820 .0530 .564 .0256 2.61 .0129 .0578 -.153
h
.872 .694 352 .783 .943 .El4 .938 324 343 350 .877 .483 .827 .953 .998 .086 .990 .992 .997 .86 1 .975 373 .968 367 .957 .I75 .999 .352 393
Ra
47.93: 63.06' ?178.4g 4.289' 19.08' 4.798' 14.73k 3.020' 5.448' 2.251' 480.0f .4961 9.884'
.015'
7.968J .929' 1.322' 2.382k 4.042' 1.966' 3.638' 3.163' 2.461' 3.897' 3.347l .759l 3.240' 14.98' 103.1k
Fb rc
.194 .228 .304 .876k 363' 371 363 .727 .714 ,727 .714 .133 .080 .758 .916 .484 346 .846 346 .82tik 346 .828k 346 .823 .859 .828k 346 .083 .312
Table XVI-(continued)
.603 .975 .912 .528 .290 .382 .228 .396 .372 .444 .402 .906 .161 .122 .120 .429 .0621 .0466 .0263 .765 .259 .664 .269 ,626 .304 2.12 .115 SO8 .161
d
Sest
d
1.18 2.03O 2.09" 2.00' 1.10' 1.45' 364' .904" 360" 1.01" .931" 2.57O .46lP .406h .462" 1.13p .21.Sh .16lg .0909g 2.16". 396' 1.21". .92$ 1.98' 1.22" 6.00" .397g 1.19p .444"
sff
1.1Sk 2.01" 1.94' 3.06" 1.69" 2.22" 1.33" 1.36O 1.42' 1.53O 1.54p 7.23" 1.35k 1.09 .791" 1.96' .598h .449g .253g 3.86O 2.5Ok .59l0 2.59m 3.24O 3.12" 10.7O 1.1og .933" .342g
spd
.371k .826m .949" .346g .231k .272' .181k .326g .382' .366g .4 13' 3110 .144' .120g .120; .416 .0615g .046 1 .0260e .531m .257p 1.7fim .266' .475" .303' 1.47m .114p .268' .0896m
d Sh
4 6 5 10 8
5
6 5 6 5
5 5 5
8 6 6 4 7
5
6
5
4 6
5
4 6 4
5
8
nq
vI
E
15-49-1 15-49-2 15-50 15-51-1 15-51-2 15-52-1 15-52-2 15-53-1 15-53-2 15-54 15-55 15-56 15-57 15-58 15-59 15-60 15-61 15-62 15-63-1 15-63-2 16-64-1 15-64-2 15-65-1 1565-2 15-66-1 15-66-2 15-67 1568 15-69 15-70 15-71 15-72- 1
.432 2.86 1.78 ,222 3.18 -.485 2.80 -5.86 -.803 -4.91 -4.67 -3.31 -3.73 -4.75 -4.12 -4.08 -2.96 -8.91 -3.88 -2.94 -3.62 -2.90 -2.05 .5 14 -.865 -.284 2.58 2.46 2.08 2.66 1.70 3.73
3.40 3.48 11.3 3.05 2.46 .736 2.18 .809 .55 1 -4.23 -3.91 -3.96 -4.73 -4.02 -3.85 -4.25 -1.65 -13.3 -2.02 -1.80 2.58 2.75 2.71 2.88 4.27 4.40 8.07 .905 12.6 1.98 5.90 -6.56 1.48 .47 1 .673 4.56 3.18 2.04 .587 q SO6 3.07 -.132 -.lo7 -.857 -1.04 -.534 -.811 -4.30 -4.16 -1.28 1.54 .990 ,713 .292 1.20 .783 .966 .626 -6.13 -5.62 -7.11 -6.54 -4.82 -4.78 .680 .995 .640 .895 .129 .915 ,766 .437 .993 .995 .825 .799 .939 .989 .980 .99999 .975 .906 .9997 .900 .995 .675 .996 .852 .981 .925 .871 .981 ,894 .859 .793
355
3.019: 6.8 14' 53.39k 1.385' 6.043k .034' 5.148' 2.842' .236' 37.48' 50.22k 1.068' .885' 14.90' 87.3Ie 12.4 1' 20408: 9.598' 4.581' 928.5' 4.287' 50.23k .839' 71.02k 2.640' 12.801 20.77' 6.270k 52.3If 5.991k 9.824' 2.548' .062 .821 .198 .262 .lo3 .017 .130 .04 1 .556 .556 .854 .854 .617 .659 .869 .384 .636 .381 .330 .381 .330 .381 .330 .381 .330 .090 .303 .303 .271. .747' ,791
.loo .842 .662 .197 .948 .540 1.10 .378 .968 .487 .205 .167 .739 .992 .347 .219 .197 .00625 .835 .781 ,0387 .609 .136 .603 .0803 .5 16 .248 .523 .543 .3 75 .617 .764 .946 .964" 2.26p 1.61m 2.21p .95Sk 2.56k 1.88' S91k .482k 6.25' 8.39O .873g .321e 1.74" .0148' 2.07m 1.59m ,085 lh 1.24k .299k 1.22p .177" 1.05" .545' .679g .76d .524h .863k 1.24" 1.81m
1.68p 1.64m 2.62m 1 .90m l.lom 4.59p 1.60" 2.11' 1.06' .638k S21k 3.41" 4.58: 1.08' .633' l.Olrn .0340h 6.38" 2.81' .14d 2.19" .490m 2.17" .289k 1.86m .894m 1.66g 2.35' 1.62g 2.91' 3.33m 6.10"
1.4 1; 1.11' 2.60" .90lg .682h .862k .392" .792g .669 .157' .128' ,479" .642" .20Sk .16Og .14d .00520e 1.39' .658m .0378' S13" .133" .508m .0785k .43sm .242" .620e .66Sg .459e .769g .596e .844h
S68j .602"
4 5 4 10 7 7 6 10 6
5
4
5
7 5 4 4 4 4 7 7 4 4 4 5 4
5
4 7 6 7
10 8
+,
h
-4.14 -3.59 -3.25 -8.75 -.189 -4.19 -2.70 .352 -.0854 -.206 .307 -.00766 -.234 .957 .958 .652 - ,464 .873 1.68 I .44 1.36 .312 1.26
R
1.32 11.5 12.0 16.5 -1.84 5.89 - 1.43 -.768 1.19 -.993 -1.02 -.724 1.04 14.2 -8.08 ,604 2.43 2.10 3.03 12.3 7.49 4.6 1 4.44
ff
2.03 .643 1.21 2.12 1.20 1.46 -1.32 .226 .708 -.201 - 1.36 -1.51 1.14 -4.63 -2.04 3.28 5.24 3.84 1.71 ,393 1.03 ,979 ,958
a For footnotes, see Table XIII.
15-72-2 15-73 15-74 15-75 15-76 15-77 15-78 15-79-1 15-79-2 15-80-1 15-80-2 15-81 15-82 15-83 15-84 15-85 15-86 15-87 15-88 15-89 15-90 15-91 15-92
Set
.976 .963 .968 .993 ,996 .998 ,999 .537 .9 19 SO3 ,945 .902 .696 .999 .977 .998 .946 398 .9994 .9991 .972 ,995 .996
Ra 20.22' 12.77k 7.385' 37.94' 70.09f 290.Sf 427.2f ,812' 6.181k .679' 12.47' 6.531k .938' 236.1' 31.23g 115.5k, 17.13' 4.164' 4 19.6:' 27 1.5' 34.72' 45.53' 67.16k
Fb
.402 .118 .0666 .099 .275 .785 .385 .06 1 ,128 .162 .817 .775. 374' .307 .307
.417
.846 .786 .824 .851 .85 1 .573 .290
rc
Table XVI-(continued)
.315 ,522 .681 .167 ,0666 .0593 .0303 .131 .0576 ,304 0.124 .221 .654 .0820 .362 ,066 .34 1 ,772 .014 .lo7 .283 .154 .I23
s:st
d
.689k 1.61° 2.33O .670m .267m .187h .129g .3070 .177' .5580 .339' .453J 1.14O .441k ,963m .223j 1.06g 2.61" , .0594j .490° 1.11" .259m .206m
sff
2.56O 4.10" 6.94" 2.37k ,945" .4 14' .0490g .613" .539m .938" .381k .682" 1.04". .708' 1.03g .129m .65 1' .952m .142! .869' 2.33' .642k .511k
d
sl3
.30Sg .416h .54sm 1.21k .483O .0732e .031Se .llSJ .117O .241" .148m .204p .517O. .0736' .221'. .0539' .203k .492" .013lg .152k .281g .A93" .154k
d Sh
4 6 4 7 5 4 4 7 4 4
5
5 7 6 7 6 6
5
5 4 4 4
5
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
117
TABLE XVII Composition of the Electrical Effect-CarbonCarbon Double-Bond Sets
15-1 15-2B2 15-3 15-4 15-5 15-6 15-7 15-8 15-9 15-10 15-11 15-12 15-13 15-14 15-15 15-16 15-17 15-18 15-19 a 01
a
5b5 44
3b7 43 a
a C
C
21 C
d b C
d C
b
15-20 15-21 15-22 15-23 15-24 15-25 15-26 15-27 15-28 15-29 15-30 15-31 15-32 15-33 15-34 15-35 15-36 15-37 15-38
76 C
looe C
looe 1 0oe 1 0oe 1 0oe 1 0oe 63 C
45 C C
C C C
C
59
15-39 15-40 15-41 15-42 15-43 1544 15-45 15-46 15-47 15-48 15-49 15-50 15-51 15-52 15-53 15-54 15-55 15-56 15-57
f C
75 74 73
6b2 C
6d8 b f f C
C C
46 C C
15-58 15-59 15-60 15-61 15-62 15-63 15-64 15-65 15-66 15-67 15-68 15-69 15-70 15-71 15-72 15-73 15-74 15-75 15-76
46 48 C
36 C
38 49 85 C
76 27 86 43 78 39 95
15-77 15-78 15-791 15-80 15-81 15-82 15-83 15-84 15-85 15-86 15-87 15-88 15-89 15-90 15-91 15-92
80 52 63 43 32
32
6d4
C C
C
is a function of OR for this set.
p is not significant for this set. Correlation is not significant for this set. is not significant for this set. Best correlated by eq. (41). 01 and p are not significant for this set. (Y
(91) have reported a correlation of values of AAGJ with the u$ constants. The AAG$ were obtained from
A A G ~= A A G t~AAG; ~
(29) where AAGz0 is the polar contribution and AAG$ the resonance contribution to the free energy. The A A G L term is calculated from the correlation of log k for the olefins whose substituents do not conjugate with the double bond. Charton (92) has examined the correlation of data for electrophilic addition to the double bond with the extended Hammett equation [eq. ( 2 ) ] . For multiply substituted sets, eq. (30) was used. This equation neglects interaction terms (98).
& = a%l,X
(30) +h Sufficient data are extant in the literature t o permit the examination of 15 sets. The sets studied are given in Table XV. The data were correlated with +flxuR,X
118
MARVIN CHARTON
eq. (2) or, where appropriate, with eq. (30). Results of the correlations are set forth in Table XVI. Slightly improved results for set 15-7 were obtained by the exclusion of the value for X = Bz. Of the 15 sets studied, 10 gave significant correlations with eq. (2) or eq. (30). Two of the five sets which did not give significant correlation had only four points, and the remaining three sets had only five points. It seems quite likely that if more points were available, significant correlation would also have been obtained for these sets. With regard to the composition of the electrical effect, examination of the p~ values reported in Table XVII shows that in six of the sets which gave significant correlation, the localized effect is predominant (in these sets, either PR < 50 or 0 is not significant). Thus it would appear that in so far as substituent effects are concerned, there are two major classes of electrophilic addition to the carbon-carbon double bond: predominance of the localized effect or predominance of the delocalized effect. This behavior may well be accounted for in terms of the reaction mechanism. The rate-determining step in the electrophilic addition reaction is believed to be the formation of an intermediate which may be either bridged or a free carbonium ion. X
X \
l
Z Y + c=c
\
X
X ZYi
l
c-c + Y e
--*
\ I
I
c=c
\
-+
‘C-l/+YQ I
\
2
4
or
I
\
I I \ Z 5
Those sets for which the resonance effect is predominant are the sets which are most likely to give rise to the free carbonium ion 5, as the substituents in these sets (sets 15-14 and 15-1 7 and possibly 15-18) are all donors by resonance, as is shown by their UR values. Those sets for which the localized effect is predominant may be accounted for in terms of intermediates 3 or 4. Sets 15-5, 15-7B2,and 15-12 gave significant values of 0. It is difficult to account for this fact in terms of intermediate 4. The results can be accounted for in terms of intermediate 3, however, if this species resembles other three-membered rings, such as cyclopropane, in its behavior. Sets 15-6, 15-8, 15-9, 15-12, and 15-15 include both donor and acceptor substituents. The successful correlation of
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 119
these sets implies that the same mechanism operates throughout the set. It would seem, then, that the formation of free carbonium ions in these sets may be excluded, as those members of the set bearing donor substituents would give 5, while those members of the set bearing acceptor substituents would give 4. As substituent effects are not the same in 4 as in 5, there would result a lack of correlation with eqs. (2) or (30). We may conclude, then, that in these sets, the addition probably proceeds via the formation of the bridged intermediate 3. As all of the substituents in set 15-19 are donors by resonance, with the exception of X = H, if a free carbonium ion were to form, it would be expected to be 5. This intermediate should show a large and significant /3 value. It would seem, therefore, that in set 15-19, the reaction again proceeds by way of the bridged intermediate 3. We have also examined the effect of substituents on orientation in the addition of BH3 to the carbon-carbon double bond. Consider the substituted ethylene XCH=CH2. The boron may become bonded either to carbon 1 or to carbon 2. The overall rate constant for the reaction is given by
where
In eq. (32), p1 and pz denote the percent of the product containing boron at C' and C 2 , respectively. Applying the extended Hammett equation to the partial rate constants kl and kz for the compound bearing the X substituent gives logk1,X =logPl,XkT,X =alul,X 'PluR,X
thl
1% k2,x = 1% P2,XkT,X = a201,x +02UR,X +h2
(33)
(34)
Subtracting eq. (34) from eq. (33) results in
or PlX log __ = atuI,X + ? h , X + h l P2x equivalent to eq. (2). The results of correlation with eq. 36 are excellent (Table XVI). It would seem that orientation in electrophilic addition can be successfully represented by the extended Hammett equation. The results obtained seem to show that orientation in the addition of 'BH3 to olefins is primarily a function of the delocalized electrical effect. The results obtained are surprising in one respect. For that member of the set for which X = H , C'is
120
MARVIN CHARTON
equivalent to C2, and therefore p l = pz = 50. Then h' should equal zero. The value actually obtained is significantly different from zero. We cannot explain this anomaly at the present time. Ledaal and co-workers (101-105) have proposed a linear free energy relationship for predicting the percent zwitterion formed at the ith carbon atom in substituted quinones, substituted dibenzoylethylenes, and substituted acetylenes. Fliszar and Granger (106) have proposed the equation AGJ,p)/2.3 RT
(37)
for the calculation of product composition, where f is the fraction of the cleavage following path a and 1 - - f the fraction of the cleavage following path b. Values of A G i calculated for various groups are reported. The A G i values for CH2Z substituents are linear in the corresponding Taft u* values. There is no overall dependence of AGxt on uI and uR, however. Vrbaski and Cvetanovid (107) have found linear relationships between the logarithm of the rate constant for the reaction of various alkenes with electrophiles and the corresponding ionization potential. b. Nucleophilic addition. The first attempt to apply a linear free energy relationship to the reactivity of substituted ethylenes undergoing nucleophilic addition is that of Friedman and Wall (108). These authors proposed the equation log kx = Pv
+ log I
(3 8)
where kx represents the rate constant for the reaction of the substituted ethylene bearing the X substituent with the anion of some amino acid, kCN represents the rate constant for the reaction of acrylonitrile with the same nucleophile, and PV is a measure of the electrical effect of X relative to that of the cyano group. These authors also reported nearly linear plots of log kx against u - u0 and against UR. A plot of log kx against u-- uo was said to give only qualitative correlation. Shenhav, Rappoport, and Patai (109) have reported a correlation of the rate constants for the addition of morpholine to substituted ethylenes with the PV values of Friedman and Wall. They also report a correlation of the rates with the UR values with p=48. This correlation was limited to substituents with UR in the range .lo-.15. Sufficient data are extant in the literature for eight sets of nucleophilic addition to substituted ethylenes. The sets studied are reported in Table XV. The data were correlated with eq. (2) and with the equation where
Qx = CwUI,X+ PJR,x+h
(39)
G,x= q , x- q x
(40)
u g , ~is defined by
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
121
The u i values reported in the review of Ritchie and Sager (8) were used. The data have also been correlated with the equation
The results of the correlations are given in Table XVI. Sets labeled A, B, and C are the correlations with eqs. (2), (39), and (41), respectively. The results for set 15-25 are improved by the exclusion of the value for X = EtCO, probably because of uncertainty in the UR value of the propionyl group. The results for sets 15-26 through 15-28 are all greatly improved by the exclusion of the value for X = CHO, most likely because of the uncertainty in the value of uR for the formyl group. Best results were obtained for correlations with eq. (41). Of the eight sets studied, six gave significant correlations with eq. (41). The two sets which did not give significant correlation with UR had only four points each and encompassed a range of only .05 u units. Obviously, the electrical effect in nucleophilic addition to the double bond is almost purely a resonance effect. In magnitude, the electrical effect is very large. The values of p obtained range from 14 to 32. This range is comparable to the range of P observed for those electrophilic addition sets for which /? was predominant, the range in that case being -13 to -33. c. Radical Addition. Herk, Stephani, and Szwarc (1 11) have discussed the rates of addition of methyl radical to substituted ethylenes bearing electron acceptor substituents in terms of the u; constants of the substituents. Abell (122) has made an attempt to correlate relative equilibrium constants for the reaction of bromine atoms with substituted ethylenes with the up constants. Price and Alfrey (1 13) have proposed a linear free energy relationship for the calculation of copolymerization reactivity ratios. Their equation is kiz = Pi Qz exp(-eiez)
(42)
where P is considered to be a function of the reactivity of the radical, Q is a function of the reactivity of the monomer, and both P and Q are composed of resonance and steric effects in the monomer. The quantity e is thought to be a polar term characteristic of both the monomer and the radical. The reactivity ratio r, is then given by kii
-
Qi
rl = - - - exp[el(ez -el)] kiz Qz
(43)
where the subscripts 1 and 2 refer to the radical derived from monomer 1 and monomers 1 and 2. Thus k l l represents the rate constant for the reaction of radical derived from monomer 1 with monomer 1 , whereas klz represents the reaction of radical derived from monomer 1 with monomer 2. The reference monomer chosen for the Price-Alfrey treatment was styrene, for which Q and e were originally defined as 1 .O and -1 .O respectively. Later, e was redefined as
MARVIN CHARTON
122
-.8 (1 14). Regrettably, Q and e values are imprecise and tend t o vary with the reactivity ratios used in their calculation (1 15). An attempt has been made to improve the Price-Alfrey equation by the assignment of different values of e to the monomer and t o the radical derived from it (1 16). Schwan and Price (1 17) have reexamined the Price-Alfrey equation, and they write it in the form
r l = exp[-(ql -qz)/RT] exp[-7.23 . 1OZ0el(el-e2)/RT] and rl rz = exp - I7.23 . 10Zo(el-ez)2/RT] or logrl = -
(ql -q2) RT
~
--
7.23 * lozo RT
and log rl +log r2 = - 7.23RT . lozo (el - ez>’ = l o g e ) + log
(2)
Shen (1 18) suggested a formal analogy between the Hammett equation and the Price-Alfrey equation. Charton and Capato (1 19) have derived relationships between e and q values and the Hammett equation as follows. From the Hammett equation,
Similarly, Then
logkll = P i a i + h
(48)
log k12 = ~
(49)
1 0 2+ h
kz 2 log - = -Pz(U1kz 1
uz)
kll kz z log - + log -- = (p1 - p z ) ( u * - az) kl2 kz 1
Assume (53) Then
(54)
and kll kz2 log - + log - = m(ul - uZ)’ kl2 kz 1
(5 5)
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
123
From eq. (47) and eq. ( 5 9 ,
or (el
-
eZ)' = bz(ol -
(57)
from which
or
Choosing H as the standard substituent, ex =b'Jxt%-'Y@H
As uH = 0 by definition, ex = b o x t % To relate q values to a constants, combine eq. (50) with eq. (53) t o give
(3
log - = (mul t c) (al - uz) Equating eq. (62) with eq. (46) gives
. lozo el(el - ez) = mal(al RT
- (92 - ql) - 2 . 2 3
RT From eq. (58), -
-.
az) t c(ul - uz)
(qz-ql) - 7'23' 'OZo e l b ( o l - o z ) = m u l ( u l - u z ) + ~ ( u 1 - u 2 ) RT RT
(63)
(64)
Writing eq. (60) for eland substituting in eq. (64) gives - (" -")
RT
Then - (ql RT where
- 7'23
*
loZo(bul + %)b(al - az) = mol(al - az) t c(ul - az) (65)
RT
= 7'23
'OZo bZu1(al - uz)t b%(ul - uz)t mal(ol
RT
-
uz)
124
MARVIN CHARTON
Thus - (‘I
-
RT
= -mul (a, - u z )+ mu, (ul- u2)+ (c + bQ) (al - u z )
(68)
or Aq = aAu Choosing H as the standard substituent gives
Combination of eqs. (46), (61), and (71) gives, after simplification,
(3
log -
= (a‘ -t b’ul) (01
+a?)
where a a’ = - t 7.23 . lOZobeH RT
(73)
and b’ = mRT
(74)
Values of e are correlated by the up constants in accord with eq. (61) (1 19, 120). Kawabata, Tsuruta, and Furukawa (121) have proposed a revised form of the Price-Alfrey equation based on the definition e = 0 for styrene. On the basis of this redefinition, they have calculated a new set of Q values. These Q values are linear in the Hammett u constants. It is not clear from their paper whether this linear relationship is for substituents directly bonded to the carbon-carbon double bond or whether it is applicable only to Q values for substituted styrenes. Charton and Capato (1 19) were unable to obtain significant correlations between any u constants and the q values of Schwan and Price (117). Zutty and Burkhart (122) have proposed a redefinition of the Price-Alfrey equation based on ethylene as the reference system with Qo and e defined as 1 and 0, respectively. Kawabata, Tsuruta, and Furukawa (121) have reported a linear relationship between the logarithms of their Q values and the logarithms of the methyl affinities of Szwarc and co-workers (111, 123, 124). James and MacCallum (125) have found a linear relationship between the logarithms of the Qo values calculated from the definition of Zutty and Burkhart (122) and the logarithms of the rates of addition of ethyl radicals to various substituted ethylenes. Similar
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
125
relationships for both Q and Qo values have been found by Bloor, Brown, and James (126). Thus, the Price-Alfrey equation is apparently applicable to the correlation of rate data for radical addition to substituted ethylenes in uses other than vinyl polymerization. Bamford and co-workers (1 27, 128, 129) have proposed the equation log k = log k3,T t C Y U + ~
(75) for the treatment of radical addition and transfer reactions. In this equation log k3,T is the rate constant for the transfer reaction of the radical with toluene, Q and 0 are reactivity parameters characteristic of the substrate, and u is the Hammett up constant. They find that the a values are given by the relationship
a = -/.Po (76) where p2 = 5 . 3 . These authors report that eq. (75) is equivalent to the Price-Alfrey equation. They suggest that the latter is best defined in terms of e = 0 for styrene. Data for 25 sets of radical additions to carbon-carbon double bonds have been correlated with eq. (2) or eq. (30). The sets studied are set forth in Table XV. Results of the correlations are reported in Table XVI. Many of the sets were improved by the exclusion of some points. In particular, exclusion of values for phenyl and vinyl substituents almost invariably resulted in improved correlation. Of the 25 sets studied here, 1 4 gave significant correlation. The great majority of the sets which did not give significant correlation had only four to five points. Had more data been available, improved correlation would probably have resulted. It would therefore seem that rate data for radical addition to the carbon-carbon double bond are correlated by the extended Hammett equation. The results obtained are not as good as those usually obtained for correlations with the extended Hammett equation. Thus, of the 14 sets which gave significant correlation with eq. ( 2 ) , one gave excellent, one gave very good, four gave good, four gave fair, and four gave poor results. There seems to be considerably more scatter in the extended Hammett equation correlations of rate data for radical addition than is observed for other types of addition, or indeed for other systems in general. There may well be an additional factor in the reactivity of substituted ethylenes to radical addition other than those represented by the usual electrical effects. Certainly the Q parameters of Price and Alfrey and the 0 parameters of Bamford and co-workers are not well related to the UI and UR constants. As to the nature of the factor which Q and 0 represent, it has been suggested to be a resonance effect and perhaps a steric effect as well. If it is indeed a resonance effect, then it is in addition to the resonance effect represented by OR. The results obtained show that radicals can be divided into two classes depending on the signs of a and 0. The methyl, ethyl, and cyclopropyl radicals
126
MARVIN CHARTON
gave positive values of a! and 0. These radicals may be classified as nucleophilic. The difluoroamino radicals and bromine atoms gave negative values of (Y and p . These species may be classified as electrophilic radicals. The magnitude of the electrical effect is somewhat less in the case of radical addition than it was in the case of electrophilic and nucleophilic addition. In so far as the composition of the electrical effect is considered, the values of pR given in Table XVII show that for both nucleophilic and electrophilic radicals, the resonance effect seems to predominate, probably in the case of the former and almost certainly in the case of the latter. d. Carbene Addition. Skell and Cholod (140) have correlated log krel for the reaction of alkenes with dichlorocarbene with eq. (28). They obtained results comparable to those of Dubois and Mouvier (89) for the addition of bromine to alkenes. Moss and Mamantov (141) have also noted a dependence of rate of addition of dichlorocarbene t o alkyl ethylenes on the Taft steric parameters. Skell and Cholod have also fitted linear free energy relationships between rates of addition of various carbenes to alkenes. A relationship between log k and the ionization potentials of the alkene was also reported. Only four sets of data are available for the addition of carbenes to substituted ethylenes, all of them involving dichlorocarbene. The sets studied are given in Table XV. Results of the correlations are reported in Table XVI. Of the four sets studied, only one gave significant correlation. This fact is understandable because there are only four points in each set. The magnitude of the electrical effect is less than that observed for most electrophilic additions and is comparable to that found for radical reactions. As expected, dichlorocarbene is electrophilic. The composition of the electrical effect based on the limited evidence available is different from that found for electrophilic, nucleophilic, or radical addition. The value of pR for the set which gave significant correlation shows that the localized and delocalized effects are both important, with the former being somewhat the larger. e. Diels-Alder Cycloaddition. The application of the extended Hammett equation t o reaction rates for the Diels-Alder reaction was reported by Charton (142). Also studied were the para : meta ratios obtained in the addition of substituted ethylenes to isoprene. Inukai and Kojima (143) have reported a correlation of log prf(c) - log prf(u) for 2-substituted-l,3-butadienesreacting with methyl acrylate with the simple Hammett equation using the u+ constants. The prf are partial rate factors for reaction at positions 1 and 4 of the butadiene, the c and u standing for the AICIJ catalyzed and uncatalyzed reactions, respectively. Data for 21 sets of reaction rates have been correlated with eq. (2) or eq. (30). Also correlated were data on the meta : para ratio in the product of the reaction of isoprene with substituted ethylenes, and the syn-exo-anti-endo and
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
127
syn-endo-anti-endo ratios for the reaction of substituted ethylenes with perchlorocyclopentadiene. The sets studied are reported in Table XV. Results of the correlations are given in Table XVI. Best results for sets 15-63 t o 15-66 were obtained on the exclusion of the phenyl group. Of the 11 sets of substituted dienophiles studied, eight gave significant correlations. The trans1,2-disubstituted ethylenes gave generally good results. The results obtained for the cis-l,2-disubstituted ethylenes were usually inferior to those obtained for the trans-I ,2-disubstituted ethylenes. The only set of 1,l-disubstituted ethylenes studied gave excellent results. The substituted ethylene-cinnamaldehyde reaction also gave excellent results. Significant results were obtained for a correlation of the ratio of percent para product to the percent meta product in the reaction of isoprene with substituted ethylenes (set 15-79) on exclusion of the value for the phenyl group. The correlation of the ratio of percent syn-endo to percent anti-endo and percent syn-em to percent anti-endo are successfully correlated with eq. (2), the former set (15-80) after exclusion of the value for the methyl group. In the case of substituted dienes, the electrical effect is comparable in magnitude to that observed for radical addition reactions. The magnitude of the electrical effect apparently is solvent dependent, as is seen from sets 15-58 and 15-61. In so far as the composition of the electrical effect is concerned, substituted diene sets generally show pR values in the range 36-49 (pR values are set forth in Table XVII). With regard to the magnitude of the electrical effect in substituted dienophiles, comparatively low values of a! are observed for these sets. The composition of the electrical effect depends strongly on whether the cis or the trans configuration is being considered. The cis compounds show values of pR in the range 27-43, which indicates predominance of the localized effect. The trans compounds show values of pR in the range 76-95, which shows considerable predominance of the delocalized effect. The only set of 1,l -disubstituted ethylenes available also shows predominance of the delocalized effect, with a pR value of 80. The reaction of substituted ethylenes with cinnamaldehyde (set 15-78) shows a comparatively small value of a!, with a p~ value of 52. Orientation in the Diels-Alder reaction (set 15-79) shows a moderate dependence on electrical effects, with the resonance effect predominant (pR = 63). Product configuration in the Diels-Alder reaction (sets 15-80, 15-81) also show a moderate dependence on electrical effects. In this case, however, the localized effect is predominant. Following the work of Charton (142), we may draw certain mechanistic conclusions from the results reported above. Let us begin by considering the question of a two-step versus a concerted mechanism. T o define exactly what we mean by these terms, we shall consider any mechanism for which the reaction coordinate proceeds from reactants through a single transition state to products as concerted and any mechanism for which the reaction coordinate proceeds
128
MARVIN CHARTON
from reactants through a transition state followed by an intermediate and then a second transition state to products as a two-step mechanism. We may now consider what the effect of substituents on the reactivity of the diene must be in the case of the concerted mechanism. For the 2-substituted-l,3-butadienes, log kxl= a 1 2 0 1 , ~ '+ a 4 2 0
1 , +~P ~ i 2 (JR,x2
842 %,x'
(77)
+h
where a12represents the magnitude of the localized effect at C, exerted by the substituent at C2 in the transition state 6 and the other coefficients having analogous meanings. Then log kx2 = CYCJI,~~ +/~uR,+ x ~h (78) where eq. (78) is equivalent to eq. (21, = a12
8 = 8 1 2 '042
@42 >
6
I
(79)
8
Now for the 2,3-disubstituted butadienes, we may write 1% k X z X 3 = a12uI,X2 + a 4 2 0 I , X 2 +ff13u1,X3 t a 4 3 u 1 , X 3 + P 1 2 0 R , X 2 +8420R,X2 t8130R,X3 +0430R,X3
+h
(80)
If the reaction of the 2,3-disubstituted-l,3-butadienes is with a symmetric dienophile, such as maleic anhydride, the 2 and 3 positions in the diene are equivalent, and therefore a12
= ff43,
&13
= a42,
812
= 843,
PI3
= 842,
(8 1)
thus giving
1%
kX2X3 = a(uI,X2
01,X3)
+ 8((JR,X2
(82)
uR,X3)+h
equivalent t o eq. (30). Let us now consider the effect of substituents on the diene in the event of the two-step mechanism. There are three possible cases which must be examined. (a) The first step is rate determining. (b) The second step is rate determining. (c) Both steps are comparable in rate. We may begin by considering case (a) for 2-substituted-l,3-butadienes 7 and 8. Considering transition state 7, we may write 1% kxl = a 4 2 0 1 , x l + 8 4 2 %,X2 + h (83) For the 2,3-disubstituted butadienes, we obtain log kx2x3= f f 4 2 0 1 , X 2
+a4301,X3 +P42(JR,X2 + 8 4 3 % , x 3
+h
(84)
Equations equivalent to eq. (83) and eq. (84) can be written from a consideration of transition state 8. Analogous equations can be written for case
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
129
(b). For the third case, equations analogous to eq. (77) and eq. (80) may be written. On comparing the concerted and the two-step mechanisms, we conclude that the rate constants for the reaction of the 2,3-disubstituted-l,3-butadienes with symmetric dienophiles should be successfully correlated by eq. (30), giving values of a and equal to those obtained by the correlation of the rate constants of 2-substituted-I ,3-butadiene (reacting with the same dienophile) with eq. (2) if the mechanism is concerted. If the mechanism is two step, then the rate constant for the reaction of the 2,3-disubstituted-l,3-butadieneswith symmetric dienophiles should nor be correlated by eq. (30) unless X2 and X3 are identical, and furthermore, the values of a and p obtained from the correlation of the rate constants for the 2,3-disubstituted-l,3-butadieneswith eq. (30) should not be equal to the values of a and obtained for the correlation of the rate constants for the reaction of 2-substituted butadienes with eq. (2). Obviously, in this discussion it is assumed that both monosubstituted and disubstituted dienes are reacting under the same conditions with the same dienophile. The results obtained for sets 15-58 and 15-59 show that the a and p values do not differ significantly, as is shown by the student t tests. Furthermore, set l(5-59 is correlated by eq. (30) although it contains members for which X2 f X 3 . We are therefore forced to conclude that the mechanism in this case is concerted. The successful correlation of set 15-61 with eq. (30) suggests, although it does not conclusively prove, that this reaction is also concerted. The dienophiles may be treated in an analogous manner. For a substituted dienophile reacting with a symmetric diene through transition state 6, we may write (85) log k x s = a55 0 1 , ~f a 6 5 01,X 0 5 5 0 R . X + P 6 5 01,X = (O55
a65)01,X
= ff'U1,x + 0
(P55
(86)
+h
P6S)'R,X
' 0 t~h ~
(87)
while for a disubstituted dienophile,
1% kxs x6 = as 5 0 1 , x ~
a 5 6 01,X6
a 6 5 01,x5
f
(y66 'JI,X6 + & 5
01,~'
+P6501,xs +@s601,x6+P6601,x6
fh
(88)
Now for reaction with a symmetrical diene a56
= a65,
a55
'
'
Then log k X s X 6 = a55(uI,Xs
uI,X6)
= a66,
a56(u1,Xs
056
= 065,
065
= 066
O1,X6) ff155('R,XS 056(0R,Xs
= aY01,xs
+ 0 I , x 6 ) +PYOR,XS + 0 R , x 6 )
+h
(89)
+0R,X6)
'
uR,X6)
h
(90) (91)
130
MARVIN CHARTON
We may now consider the possibility of a two-step mechanism. Again, there are three cases to examine: (a) step one is rate determining; (b) step two is rate determining; and (c) both steps are comparable in rate. Let us now take up case (a). For a substituted dienophile reacting with a symmetric diene, we may have either transition state 7 or transition state 8, or both. Considering transition state 8 leads to the expression
1% kx5 = ass QI,x' For disubstituted dienophiles, we have logkXsX6 =&.5u1,Xs
tQ56u1,X6
+&S
h
OR,Xs
tPS50k,X5
tP56'R,X6
(92) th
(93)
Equations equivalent to eqs. (92) and (93) can be written for transition state 9. For case (b), the transition states 9 and 10 may be considered.
4
9
4
10
For these transition states, equations analogous to eqs. (92) and (93) may be written. For case (c), we may obtain equations analogous t o eqs. (85) and (88) which are not capable of further simplification. From the above discussion, we see that in the event of the concerted mechanism, the rate constants for the reaction of the disubstituted dienophiles with symmetric dienes should be successfully correlated by eq. (30), which should result in values of Q and 0 equal to those obtained from the correlation of the rate constants of substituted dienophiles (with the same diene under the same reaction conditions) with eq.(2). In the event of the two-step mechanism, the rate constants for the reaction of the disubstituted dienophiles with symmetric dienes should not be correlated by eq. (30) unless the two substituents are identical. In addition, the values of a and /3 obtained from the correlation of rate constants for disubstituted dienophiles with eq. (30) should not be equal to the values of a and /3 obtained for the correlation of the rate constants of substituted dienophiles with eq. (2). Although sufficient data to provide thorough tests of mechanism are lacking, it is possible to make some tentative conclusions. Sets 15-67, 15-69, and 15-71 give highly significant correlations with eq. (30). These sets include both monosubstituted and disubstituted dienophiles. Obviously, then, both monosubstituted and disubstituted dienophiles lie on the same correlation line and have the same values of a and /3. It therefore seems likely that these sets undergo a concerted mechanism. The results described above have been criticized by Dewar and Pyron (145). These authors suggest that the above analysis requires that the effect of
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
131
substituents be additive in the case of the concerted mechanism and that small but significant deviations from additivity occur in the case of the substituted dienes. We reject the proposal that these deviations are significant. If they were, (Y and /3 for the monosubstituted dienes would not be equal to (Y and /3 for the disubstituted dienes unless the deviations were of just the right magnitude and direction in all of the compounds to, in effect, cancel out. Because the latter event is of a very low order of probability, we conclude that our original analysis was probably correct and that the criticism of Dewar and Pyron is entirely unwarranted. The latter authors state that no conclusion can be reached in the case of the substituted dienophles because the rate constant for the reaction of ethylene with cyclopentadiene is unknown. This statement is true for their method of assessing additivity, w h c h depends on comparing the differences log kx5 - log with log kxsx6 - log kxs. This comparison is not required for an evaluation by the Hammett equation. The method of Dewar and Pyron suffers from the disadvantage that hydrogen is not always a well behaved substituent and often deviates from a Hammett plot. Thus, for example, the value for the unsubstituted compound deviates considerably in the Hammett correlations of substituted propiolic acids. Dewar and Pyron have made use of their method to determine the mechanism of the reaction of isoprene with substituted dienophiles. They conclude that the mechanism in this system is not one which passes through a single symmetrical transition state. This conclusion is unwarranted in our opinion because the method of Dewar and Pyron, like the method of Charton, should be restricted to the reaction of substituted dienophile with a symmetric diene. Isoprene is not a symmetric diene, and therefore the analysis is not applicable. Even if by chance the conclusion of Dewar and Pyron regarding the mechanism for this reaction is correct, it in no way implies that the reaction of dienophiles with symmetric dienes does not go through a concerted symmetric transition state. We conclude, therefore, that our analysis of the reaction of substituted dienophiles with symmetric dienes is correct and that sets 15-67, 15-69, and 15-7 1 probably d o react via a concerted symmetric transition state. We may now proceed to an analysis of the significance of the /3 values. If the transition state were close t o the product, then the fl values of the disubstituted ethylenes should be small, because in the product, the substituent is bonded to an sp3 hybridized carbon atom. Thus, it is incapable of resonance interaction. As the observed values of /3 for the trans-disubstituted dienophiles are very large, we conclude that the transition state is closer to reactants than t o products. The cis-disubstituted dienophiles show a much smaller value of /3 than do the trans compounds. It therefore seems likely that the transition state for the cis compounds will be closer to product than is the transition state for the trans compounds. The values of /3 for the reaction of the trans-disubstituted dienophiles with 9,1O-dimethylanthracene, while large, are much smaller than
132
MARVIN CHARTON
the values of 0 obtained for the trans-disubstituted-dienophile-cyclopentadiene reaction or the trans-disubstituted-dienophile-2,3-dimethylbutadiene reaction. Again, this fact may be ascribed to the location of the transition state on the reaction coordinate.
f. 1,3-Dipolar Cycloaddition. Sufficient data are extant in the literature to permit the study of 11 sets of 1,3-dipolar cycloaddition reactions. The sets studied are set forth in Table XV. The data were correlated with eq. (2). The results of the correlations are reported in Table XVI. Of the 11 sets studied, seven gave significant correlations. Of the four sets for which correlation was not significant, two had only four points: the other two had five points. With respect to the electrical effect, the reactions may be classified into electrophilic sets (set 15-84) and nucleophilic sets (sets 15-85, 15-86, 15-88 to 15-90, 15-92). The nucleophilic sets may again be divided into those for which the localized effect is predominant (sets 15-85, 15-86) and those for which the resonance effect is predominant (sets 15-88 to 15-90, 15-92), as is shown by the results in Table WII. It would seem from the results of these correlations that the 1,3-dipolar cycloaddition reaction proceeds via more than one mechanism. The mechanism seems to be strongly dependent upon the reagent. The benzonitrile oxide, 11, and diphenylnitrilimine additions, 12, both show a predominance of the localized effect, while the diphenyldiazomethane, 13, and the N-methyl-Cphenylnitrone, 14, additions show a predominance of the delocalized effect. The most obvious difference among these reagents is that in the most stable contributing structures of 11 and 12, there is a C-N double bond, whereas in the most stable contributing structures 'a .. . . ph-&-Oe 11
PhC-N-N-Ph 12
Ph,-C-NrN13
Ph-8H-NMe-O? 14
of 13 and 14, there is a C-N single bond. It is not clear at present how this structural difference is involved in the susceptibility of the reaction to electrical effects. The nature of the reagent in 1,3-dipolar cycloaddition is such that almost all such reagents are not symmetric. This fact obviates the use of the mechanistic test described above for the Diels-Alder reaction. The magnitude of the electrical effect in the 1,3-dipolar cycloaddition reaction is roughly comparable to that of substituted dienophiles in the Diels-Alder reaction. 111. SUBSTITUENTS ON CARBON-HETEROATOM DOUBLE BONDS
Perhaps the largest class of nonaromatic unsaturated systems is that of the carbon-heteroatom double bonds, including as it does the carbonyl compounds,
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
133
imines, and thiocarbonyl compounds. We shall find it useful to divide the members of this group into five categories: substituted heterovinyl sets, heterovinylidene sets, heterovinylene sets with heteroatom reaction sites, trans-heterovinylene sets, cis-heterovinylene sets, and amidines and carboxylic acids. A. Substituted Heterovinyl Sets Some physical properties of substituted heterovinyl compounds may be correlated with the extended Hammett equation. Such properties include the ionization potentials and Raman spectra. The correlation of ionization potentials with eq. (2) has been described previously. Data are extant in the literature for six sets of carbonyl compound ionization potentials. The sets studied are reported in Table XVIII. Results of the correlations with eq. (2) or eq. (30) are set forth in Table XIX. Of the six sets studied, four gave significant results (18-1, 18-2, 18-5, 18-6). The poor results obtained for the substituted propionyl derivatives (set 18-3) probably result from the fact that this set contains only two substituent types, alkyl and alkoxy or hydroxy groups. Set 18-6 is improved significantly by the exclusion of the value for X = H (set 18-6-2).The magnitude of the electrical effect is somewhat greater than that observed previously for substituted ethylenes and propenes. The composition of the electrical effect is best described in terms of the pR values, which are given in Table XX. The carbonyl compounds show values of pR of 26 or less, whereas the substituted ethylenes and propenes show pR values of 66 and 69, respectively. This large and significant difference in the composition of the electrical effect has been interpreted as resulting from the loss of an n electron in the case of the carbonyl compounds and a n electron in the case of the olefins (47). Data are available for two sets of Raman spectra of substituted heterovinyl compounds. The data TABLE XVIII Substituted Heterovinyl Sets Set
Q
18-1 18-2 18-3 184 18-5 18-6 18-7 18-8
I I I I I I
Substrate
Substituted forrnyl derivatives (HCOX) ” acetyl ” (MeCOX) ” propionyl ” (EtCOX) ” carbethoxyl ” (EtOCOX) ” benzoyl ” (PhCOX) ” carbonyl ” (X’COX2) vco ” acryloyl *’ (C,H,COX) vco ” rnethacryloyl” (H,C=CMeCOX)
Ref.
47 47 47 47 47 47 152 152
c
P
W
18-1 18-2 18-3 184 18.5 186-1 186-2 18-7 18-8
Set
h
1.27 10.42 .738 9.71 .996 9.78 4.60 10.52 -.138 9.38 2.32 9.95 .858 9.58 -49.8 1618. 5.43 1648.
P
a For footnotes, see Table XIII.
3.58 2.90 3.16 -.190 2.27 4.36 4.92 -43.9 -27.2
Q
Fb
10.35' 15.9Se 2.516' 4.522' 48.70f. 7.571' 20.47: 34.11' 90.54'
Ra .849 .862 .791 ,867 .980 .889 .965 .986 .995
.527 ,297 .949h .534 .342 .075 .163 .394 ,394
rc ,390 ,330 .267 .149 .134 .658 .424 2.87 .778
Sest
d
.192e .136e .236e .137e .0811e .353e .269e 2.86e ,775
.4631 .323' 1.42O 1.67k .249O 2.39" 1.64O 6.16h 1.67 .790g .517e 2.37" .42S0 .251e .793' 9.37' 2.54
l.lBJ
sg
ssd
4
Results of Correlations of Substituted Heterovinyl Sets
TABLE XIX
11 14 6 6 7 7 6 5 5
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
135
TABLE XX Values of p~ for Substituted Heterovinyl Sets Set
PR
Set
PR
18-1 18-2 18-3 18-4
26 20 a
18-5 18-6-2 18-7 18-8
b
a
a Correlation was
53 a
not significant for this
set.
The p value was not significant for this set.
studied are reported in Table XVIII, the results of the correlations are given in Table XIX, and the pR values are set forth in Table XX. Of the two sets studied, one gave significant results. Thus, the results are too sparse to permit any conclusions to be drawn.
B. Heterovinylidene Sets The correlation of data for vinylidene sets with the Hammett equation was first reported by Charton (48). Sufficient data are available in the literature for nine sets of substituted vinylidene compounds. The sets studied are shown in Table XXI. Results of the correlations are shown in Table XXII and values of p~ are given in Table XXIII. Of the nine sets studied, six gave significant correlation with eq.(2). Of the three sets which did not give significant correlation, two have only four points, and the other set has five points. It seems entirely possible that improved correlation would have resulted had more data been available. The magnitude of the electrical effect is roughly comparable to that observed for vinylidene sets. For the substituted carbonylacetic acids, the substituted-3carbonyl propanoic acids, the anti-substituted oximino acids, and to a much lesser extent, for the substituted 3-carbonyl-2-azapropanoic acids, the localized effect predominates. For the substituted carbonylmethylene triphenylphosphorane sets (sets 21-8 and 21-9), the delocalized effect is decidedly predominant. These sets are not typical vinylidene sets, as is seen from a consideration of the contributing structures 15, 16, and particularly 17. With respect t o reaction at C', contributing structure 17 puts Ph, E C ' H-CZ-X*Ph, -P-C-C-X*Ph, II
I1
+
16
/x \
0: 8
0
0 15
+
-P-CH=C
17
21 -1 21-2 21-3 21-4 21-5 21-6-1 21-6-2 21-7 21-8 21-9
Set
21-9
21-8
21-1 21-2 21-3 214 21-5 21-6 21-7
Set
-1.57 -.479 -.384 -.342 -1.08 -.592 -.656 -.575 -8.37 -7.37
P 3.29 4.61 4.58 4.64 2.98 3.55 3.52 2.86 5.24 -.208
h
CHCI,
80% EtOH-H,O
HZO HZ0 H2O H2O HZO H*O H,O
Solvent
.942 .865 .882 .849 ,948 .874 ,936 .993 ,992 ,996
Ra 15.80i. 7.413’ 1.748’ 2.589’ 13.23’ 6.45gk 10.66J 33.92’ 117.3e 190.8e
Fb
.071 .027 .054 ,035 ,496 .482 .512 .262 .462 .763
rc
,314 .179 ,199 .162 ,120 .lo2 .0845 .0399 .355 .138
Sest d
TABLE XXII Results of Correlations of Heterovinylidene Sets
Substituted carbonylacetic acids Substituted 3-carbonyl propanoic acids ” 4 ” butanoic ” ” 5 ” pentanoic ” anti ” oximinocar6oxylic ’’ 3 carbonyl-2-azapropanoic acids ” 3-thiocarbonyl-2-thiapropanoic acids Substituted carbonylmethylene triphenylphosphoranes Substituted carbonylmethylene triDhenvlDhosDhoranes
Substrate
a For footnotes, see Table XIII.
-3.78 -1.53 -1.08 -.802 -2.39 -.781 -.907 -.368 -3.24 -5.40
(Y
lo4 kI
Q
TABLE XXI Heterovinylidene Sets
4 .528j ,830: .243m .47d .698” ,338” .273” .465” .490h 1.10”. .406m .165’ .142h .346k .0698k .160” .579e 1.49k .796g .433e
sa d
BzH
0.1 MNaCIO,
Reagent
s$
155
155
7 8 4 5 6 7 6 4 7 6
nq
48 48 48 48 48 64,5 154
Ref.
.344e .Isle .227J .181g .116e .0524e* .0467e .0404g .234e .0907m
40
25 25 25 25 25 25 25
T“C
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
137
TABLE XXIII Values of p R for Substituted Vinylidene Sets Set
PR
Set
PR
21-1 2 1-2 21-3 21-4 2 1-5
29
21-6-2 21-7 21-8 21-9
42
a b b
a
b
72 58
a p was not significant for this set. Correlation was not significant for this
set.
the substituent in a cis- or trans-vinylene position. This may be in agreement with the composition of the electrical effect for these sets. It would seem, therefore, that contributing structure 17 may be of considerable importance in the overall structure of the substituted carbonylmethylene triphenylphosphoranes.
C. Heterovinylene Sets with Heteroatom Reaction Sites It is convenient to divide the heterovinylene sets into two classes, those in which the heteroatom is the reaction site and those in which some reaction site is bonded to the heteroatom. The first of these classes will be considered here. There are three major categories of data to be considered. They are proton transfer reactions, hydrogen-bonding complex formation, and Lewis-acid complex formation. There are also three structural types to be Considered: carbonyl derivatives, thiocarbonyl derivatives, and imines. Of the three categories of data, let us begin by considering the proton transfer reactions. These are represented by pKa data. In the interpretation of these data, two major problems arise. The first of these involves geometric isomerism. Consider the protonation of some carbonyl derivative, 18. This substance may undergo protonation with an acid HA to produce either the cis- or the trans-protonated forms 19 and 20. In 18, X represents the variable substituent and Z is a constant substituent. The protonated forms are designated cis or trans, depending on the relationship of the proton to the variable substituent, X. A similar equilibrium may be written for the thiocarbonyl derivative, 21, giving the protonated forms 22 and 23, while for the imines, the protonated form 24 exists in equilibrium with the cis and trans imines, 25 and 26. Olah, White, and O’Brien (156) have reviewed the problem of “conformation” in protonated carbonyl and thiocarbonyl derivatives and in imines. They report that in the case of aldehydes and
138
MARVIN CHARTON
ketones, the predominant protonated species is that with the proton cis t o the smaller of the two groups X and Z.
20
18
II @S
II
S
h
23
II
II
26
dNyH 24
ll
9” H 22
21
N ‘H
19
II
Q“ 25
The second problem involves the measurement of pKa values for carbonyl and thiocarbonyl derivatives. Grieg and Johnson (1 57) have pointed out that the measurement of pKa values for very weak bases (11) is an inaccurate and arbitrary process. Of particular difficulty for our purposes is the fact that different carbonyl derivatives may require different acidity functions. As a result of this situation, no attempt was made to make correlations of pKa data for carbonyl and thiocarbonyl derivatives with eq. (2). Because accurate pKa values can be measured for imines, these values were correlated with eq. (2), although the conformational problem remains. The imine sets were first studied by Charton and Charton (73), who correlated them with eq. (2). No correlations of data for carbonyl or thiocarbonyl derivatives with eq. (2) are extant in the literature. Bhaskar, Gosavi, and Rao (158) have reported that AGO values for complex formation of substituted thioureas with iodine are a linear function of the Taft u* values. Drago, Wenz, and Carlson (159) have reported similar results for complex formation between iodine and substituted amides. Oloffson (160) has reported a linear relationship between -AH for the complex of substituted N,N-dimethylamides with SbCIS and the uI constants.
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
139
The sets studied are reported in Table X X N . Results of the correlations are set forth in Table XXV and pR values are given in Table XXVI. Of a total of 48 sets studied, 39 gave significant correlations. It would appear that eq. (2) is applicable to these data. This applicability is particularly significant in view of the fact that geometric isomerism is possible in all the cases examined here. Values of /3 for the cis and trans isomers may or may not be of the same magnitude. Values of (Y for the cis and trans isomers are almost certainly of different magnitude, however. It seems likely, then, that in a given set, all the members have comparable isomer compositions, because if within the same set the cis isomer is predominant for one group of set members and the trans isomer is predominant for another group of set members, it would seem that significant correlation with eq. (2) ought not to be observed. Unfortunately, it is not possible at present to determine which isomer is predominant within a given set. It seems likely, however, that the predominant isomer is that in which the reagent is bonded to the electron pair on the heteroatom, which is cis to the smaller of the two groups X and Z in the case of the thiocarbonyl and carbonyl derivatives. In the case of the imines, the proton in the free imine is probably cis to the smaller of the two groups X and Z. Thus, in the case of the substituted phenylimines (set 24-l), the predominant isomer is probably 25, where Z is phenyl. In the majority of the sets studied, the localized effect is predominant. A significant exception to this generalization is the case of the equilibrium constants for complex formation of the substituted amides with phenol and with pentachlorophenol. These sets (set 24-3 through 24-16) show predominance of the delocalized effect. It is interesting to note that equilibrium constants for complex formation of substituted N,N-dimethylthioamides with phenol and with ethanol show predominance of the localized effect. It is also noteworthy that correlation of -AH for complex formation of phenol with substituted N,N-dimethylamides shows predominance of the localized effect (sets 24-26, 24-27), as do also AvOH for complex formation between substituted N,N-dimethylamides and phenol (set 24-29), equilibrium constants for complex formation between substituted N,N-dimethylamides with iodine (Set 24-38), and -AH for complex formation between substituted N,N-dimethylamides and SbCls (set 2444). We are unable at the present time to explain this striking difference in behavior. It may be significant, however, that in all the sets in which the localized effect predominated, the W e 2 group is the constant substituent, whereas in those sets in which the delocalized effect predominates, the constant substituent is the NEt2 group or still larger groups. It is conceivable that in the case of the NMe2 group, the complex involves isomers analogous to 20 or 23, whereas in the case of the other N,N-disubstituted amides, the complex involves isomers analogous to 19.
PKa
24-1 24-2 24-3 24-4 24-5 24-6 24-1 24-8 24-9 24-10 24-1 1 24-12 24-13 24-14 24-15 24-16 24-1 7 24-18 24-19 24-20 24-2 1
Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke Ke
HNP~
Q
Set
N,N-dihexylamides
”
”
N,N-dimethylamides N,N-dimethylthioamides
piperidides
”
”
N,N-diphenylamides
”
Substituted phenylimines ” ethyl imidates ” N, N-diethylamides
Substrate
CCI,
MeNO,
H2O
Solvent
79
PhOH
pentachlorophenol
PhOH
pentachlorophenol
PhOH
pentachlorophenol
PhOH
pentachlorophenol
PhOH
Reagent
Heterovinylene Sets with Heteroatom Reaction Sites
TABLE XXIV
20 50 20 50 20 50 20 50 20 50 20 50 20 50 20 50 25 20 35
25
r C
73 73 161 161 161 161 161 161 161 161 161 161 161 161 161 161 16 1 161 162 163 163
~~
Ref.
e
c
24-22 24-23 24-24 24-25 24-26 24-27 24-28 24-29 24-30 24-3 1 24-32 24-33 24-34 24-35 24-36 24-37 24-38 24-39 24-40 24-4 1 24-4 2 24-43 24-44 24-45 24-46 24-47 24-48 acetyl derivatives
Av
Ke Ke -AH Ke -AH -AH -AH -AH
-AHO
N,N-dimethy lamides
AvOH AVOD AvOD AVOD AVOD AvOD AVOD Av Ke
N,N-dimethylamides methyl carboxylates propionyl derivatives acetyl ethyl carboxylates
acetyl derivatives ethyl carboxylates
fomyl ” ethyl carboxylates propionyl derivatives methyl carboxylates forrnyl derivatives N,N-dimethylamides
acetyl derivatives
AVOH
N,N-dimethy lamides
Ke Ke Ke Ke -AHD -AH -AH
CCl, PhH CICH,CH,Cl
CHCl,
D2O MeOD
SnCl, SbCI,
CHCl, 1,
MeOD
D,O
PhOH
EtOH
25
25 25
50 20 35 50
163 163 163 163 162 164 164 164 164 165 166 166 166 166 166 167 159 159 164 168 160 160 160 160 160 160 160
E3
24- 1 24-2 24-3 244 24-5 244 24-7 24-8 24-9 24-10 24-1 1 24-12 24-13 24-14 24- 15 24-16 24-17 24-18 24-19 24-20 24-2 1 24-22
Set
20.6 1360. -1.14 -1.15 -.633 -.386 -.997 -573 -.627 -.329 p.800 -.927 -.255 -.246 -.524 -.683 -.564 -.441 -.792 -2.03 -1.86 -1.68
a
5.41 542. -3.40 -2.81 -4.94 -5.09 -2.41 -2.22 -3.55 -3.35 -3.49 -2.76 -5.25 -4.24 -5.11 -4.36 -5.69 -6.86 -2.54 -.450 -.373 -.3 13
P 9.15 162. 1.73 1.42 1.44 1.06 1.39 1.09 1.16 .854 1.70 1.40 1.38 1.11 1.54 1.23 1.10 1.34 1.75 .975 .860 .741
h .947 .988 .9997 .994 .990 .995 .985 .980 .997 .994 .992 .99998 .996 ,996 .978 .976 .97 1 .991 .961 .975 .964 .962
Ra 17.42: 40.27' 1525.e 88.35' 51.2Si 105.3g. 32.27; 24.37' 168.6g, 88.5 1: 59.19' 29411.e 136.0g 123.1g, 21.921 20.35' 8.250' 28.09' 11.97k 18.90k 13.30k 12.36k
Fb
.200 .780 .710 .710 .710 .710 .710 .710 .710 .710 .710 .710 .710 .710 .710 .710 .713 ,713 .554 .303 .303 ,303
rc
.949 48.3 .00765 .0290 .0439 .0288 .0414 .0354 .0189 .0215 .0341 .00142 .0248 .0215 .0665 .0647 .118 ,0726 .lo7 .0826 .0889 .0824
Sest
d
4.82h 218.' .0577g ,219 .331m .217" .312k .267m .142' .162m .257k .0107e .187m .162m .501" .487" .942O .579O .314m .345: .372J .344'
d sa
Results of Correlations for Heterovinylene Sets with Heteroatom Reaction Sites
TABLE XXV
1.72j 678.O .153f: .5 781 .876' .573h .826k .70Sk .377h .428h .68d .0282e .495g .428h 1.33k 1.29k 2.38" 1.46m 1.21rn .128k .138m .127m
spd
d Sh
7 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 4 4 5 5 5 5
n"
IL)
E
24-23 24-24 24-25 24-26 24-27 24-28 24-29 24-30 24-31 24-32 24-33 24-34 24-35 24-36 24-37 24-38 24-39 24-40 2441 2442 24-43 2444 2445 2446 2447 2448
-.191 -.171 -. 126 -1.56 -.840 -3.87 -52.7 -279. -60.9 -59.5 -48.8 -6.68 -152. 120. 122. -2.49 -.837 -1.40 -2.66 -13.4 -3.95 -5.68 -13.6 -23.8 -17.5 532.
a For footnotes. see Table XIII.
-1.13 -.930 -.805 -5.38 -4.82 -5.62 -306. -388. -132. -61.1 -207. -131. -206. -87.5 -402.3 -2.17 -2.86 -1.99 -5.33 -24.0 -11.9 -21.8 -22.3 -31.5 -27.5 -281. .198 ,111 ,0658 5.91 5.69 2.99 320. 143. 148. 72.0 95.2 81.2 52.5 77.5 2252. .395 3.71 -.313 1.05 15.0 5.26 26.1 13.7 12.5 14.2 211.
.955 ,962 .926 .975 .998 .985 .99996 .980 .965 .94 1 .888 ,971 .603 .987 .989 .978 ,998 .95 1 .978 .964 .9992 .997 .99997 .996 .995 .991 10.41k 12.36k 6.035' 19.15' 124.4k 16.71' 6954.' 12.44: 20.59' 30.92e. 7.492' 16.57k .855' 19.30' 66.75f 33.72g 211.4f 4.687' 43.23f 40.19e 657.8f 166.7' 8992.' 125.9' 149.5e 84.04' ,303 .303 .303 ,554 .368 .275 .312 .344 .006 .092 .547 ,079 .997e .477 .638 .494 ,554 .275 .422 .122 .908k .341 .lo6 .557 .701, .925'
.0600 .0456 .0558 .370 .127 .404 1.07 2.88 10.9 7.54 11.0 7.24 5.71 5.75 159. ,129 .0592 .274 .257 1.47 .148 .650 .0857 .738 .565 5.95 ,2511 .191: .233 1.09' .397k 1.69m 3.30' 123.m 33.d 18.0g 56.61 22.7' 183." 17.0m 450.' .364g .174g 1.15" .573e 2.84e .842g 1.59' .214g 2.01' 2.93' 33.9
.0928m .0707m .0864" 4.21' .171m .709m 1.32h 59.2m 12.2h 8.07e 15.9' 15S0 143." 19.3' 1875.p 1.27m .694" .482" .647h 3.37' 3.44" .86d .187g 2.1 7' 1.03e 137.
.0496k .0377k .046 1" .341' .105h .409k .815' 30.1m 6.57e 2.86e 6.08e 4.949 24.9m 5.13' , 217.' .115' .0546e .278h .139' .677e .355' .625e .0615' .629' .354e 14.3
4 5 6 6
5
5 6 4 6 6 5 4 7 9 5
11 7
5 5 5 5 4 4 4 4 6
MARVIN CHARTON
144
TABLE XXVI Values of pR for Heterovinylene Sets with Heteroatom Reaction Sites
Set
pR
Set
pR
Set
24-1 24-2 24-3 24-4 24-5 24-6 24-7 24-8 24-9 24-10 24-1 1 24-12
21
24-13 24-14 24-15 24-16 24-17 24-18 24-19 24-20 24-21 24-22 24-23 24-24
b
24-25 24-26 24-27 24-28 24-29 24-30 24-31 24-32 24-33 24-34 24-35 24-36
a
75 71
71 85 81 75
b b
b C
C
d
18 a
a
a a
pR
15 C
32 49 19 a C C
Set
pR
24-37 24-38 24-39 24-40 24-4 1 24-42 24-43 2444 24-45 24-46 24-47 24-48
a a a C
33 36 a
21 38 43 39 C
was not significant for this set. was not significant for this set. CCorrelationwas not significant for this set. da and p were not significant for this set.
D. trans-Heterovinylene Sets
Data for trans-heterovinylene sets were first correlated with the extended Hammett equation by Charton and Charton (73). It must be noted that in trans-heterovinylene sets, the reaction sites and substituent are trans to each other. There are available, in the literature data for three trans-heterovinylene sets, all oximes. The sets studied are presented in Table XXVII (sets 27-1 through 27-3). Results of the cofrelations and values of pR are given in TABLE XXVII trans- and cis-Heterovinylene Sets Set
Q
Substrate
Solvent
27-1 27-2 27-3 27-4 27-5 27-6
pKa pKa pKa pKa pKa pKa
syiz-Aldoximes syn-Methylketoximes syn-Phenylketoximes anti-Aldoximes anti-Acetylketoximes anti-Phenylketoximes
H*O
"
Reagent T"C
25 25 25 25 25 25
Ref.
73,169 73, 169 '73, 169 73,169 73, 169 73,169
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
145
Tables XXVIII and XXIX, respectively. Excellent correlations were obtained for all three sets. The stereochemistry of the syn-methyl ketoximes is discussed by Charton and Charton (73). The values of p~ obtained for the transheterovinylene sets are not in good agreement with each other. Two sets gave values of 54 and 55, respectively, and the t h r d set gave a value of 35. The difference in p~ values cannot be accounted for. A value of 54 to 55 for pR suggests the possibility of some exaltation between substituent and reaction site such as that which occurs in para-substituted phenols and anilines. To demonstrate this with certainty requires that the value of pR be determined for a set of imines bearing a reaction site on the nitrogen which will not interact strongly with substituents. No such set of data is extant in the literature at the present time. TABLE XXVIII Results of Correlations for truns- and cis-Heterovinylene Sets Set
27-1 27-2 27-3 27-4 27-5 27-6 a
a
P
h
Ra
Fb
-3.35 -6.08 -4.59 -3.10 -3.28 -2.88
-3.94 -3.34 -5.64 -.627 -2.89 -1.25
10.41 11.70 11.21 11.31 8.80 11.14
.944 .999 .986 392 .950 .894
28.78e 667.2e 10.5Se
3.654' 13.95'. 7.946'
d Sh
.336 ,782 ,199 .146 .683 .175
.379 ,124 .209 .240 .359 .338
.937' .340e .431e l.lSk. .725! .80d
,773' S70' .747e 1.64' 10Sk 1.17"
.163e 10 .0758e 8 .llSe 9 .24ge 6 .176e 6 .14ge 7 -
For footnotes, see Table XIII.
TABLE XXIX Values of pR for trans- and cis-Heterovinylene Sets Set
pR
Set
pR
Set
pR
27-1 27-2
54 35
27-3 27-4
55 a
27-5 27-6
t7
a Correlation was not significant for this set.
p was not significant for this set.
No useful comparisons can be made with other systems in so far as the magnitude of the electrical effect is concerned, because unfortunately, no data are available for a set of trans-substituted enols. The values of a for the trans-heterovinylene sets can be correlated graphically with eq. (2 1) with a12= 1, X12 = 2.5. The values of p do not seem t o be a function of eq. (22).
146
MARVIN CHARTON
E. cis-Heterovinylene Sets Again, data for cis-heterovinylene sets were first correlated with the extended Hammett equation by Charton and Charton (73). There are three sets of data extant in the literature, all for oximes. The sets studied are set forth in Table XXVII (sets 2 7 4 through 27-6). Results of the correlations and values of p~ are reported in TabIesXXVIII and XIX, respectively. Of the three sets studied, two did not give significant correlation. The stereochemistry of the anti-acetyl ketoximes is discussed by Charton and Charton (73). It would seem that the localized effect is predominant in the case of the cis-heterovinylene sets. The magnitude of the electrical effect is comparable to that of the trans-heterovinylene sets. The difference in magnitude between the a values for the syn and anti phenyl ketoximes is significant and suggests that the inductive effect alone cannot account for the observed substituent effect. If the inductive effect were operating by itself, the a! values for syn and anti sets would be the same.
F. Amidines and Carboxylic Acids Amidines and carboxylic acids have been considered separately from other heterovinylene and heterovinylidene sets, because although the arnidines, 26, and carboxylic acids, 28, themselves have a heterovinylene structure, the amidinium, 27, and carboxylate, 29, ions with which they are in equilibrium have structures which are neither heterovinylene nor heterovinylidene. We shall find it convenient to discuss separately the amidines and the carboxylic acids. 1. Amidines Values of pKa for substituted amidines were correlated with the Hammett equation by Charton (190). Data are available for one set of substituted amidinium ions and one set of C-substituted-N-phenylamidiniumions. The sets studied are shown in Table XXX. Results of the correlations are set forth in Table XXXI and values of pR in Table XXXII. Significant correlations were obtained for both sets. In the case of the ionization of N-phenyl amidinium ions, the possibility of tautomerism exists. Charton (1 70) has presented arguments which suggest that the predominant tautomer is 30. The localized effect is predominant in both of the sets of amidinium ions studied.
2. Carboxylic Acids
1
Data for twenty-three sets of substituted carboxylic acid equilibria and six sets of rate data are available in the literature. It will be useful t o consider separately the equilibrium and rate data.
5
Solvent
EtOH
kr
”
5% dioxane 70% (v/v) MeOH-H,O PhH
”
D,O 80% MCS-H,O EtOH i-PrOH cyclohexanol HCONH, PhOMe Ph,O (PhCH,), 0 PhAc PhH 1,2-C6H,Cl, H,O
C-Substituted amidinium ions H2O ” ” N-phenylamidinium ions ” Substituted carboxylic acids
Substrate
PKa PKa Ka . lo5 Ka . l o 5 PKa PKa PKa PKa PKa PKa PKa PKa PKa pKa pKa PKa PKa PKa PKa Ke lo3 kr, a lo3 kr, b 10, kr log kr lo6 kr
pKa pKa pKa
30-1 30-2 30-3
30-4 30-5 30-6 30-7 30-8 30-9 30-10 30-11 30-1 2 30-13 30-14 30-15 30-16 30-17 30-18 30-19 30-20 30-21 30-22 30-23 30-24 30-25 30-26 30-27 30-28 30-29
Q
Set
TABLE XXX Amidine and Carboxylic Acid Sets
ClCH COCH C1 PhC(OMe), 5a,6pdibromocholestane Ph,CN,
SnCI, glucose
Reagent
25 30 44.08 25
28
28-30
27
5 15 18 20 25 30 35 45 25 25
25 25 0
T C
170 170 29,64, 171, 172 29,64,173 29,64,193 29,64 29,64 29,64,173 29,64,172 29,64,173 29,64, 173 174, 175 61 176 177 178 179 180 181 180 182 183 184 185 185 186 187 188 189
Ref.
a
-3.34 -1.03 -3.57 -4.07 -3.66 7.40 3.94 -3.99 -3.45 -3.27 -3.62 -5.22 -6.43 -.0765 -17.7 -19.1 -11.2 -16.9 14.0 -2.84 -9.14 -12.9 -14.0 22.00 -1.82 -.825 5.84 8.89 4.32
P 11.89 12.42 3.89 3.80 3.89 1.23 .963 4.02 3.97 3.93 3.95 4.30 6.27 11.17 8.88 8.84 5.61 4.78 -3.91 5.16 8.88 3.54 -.169 .676 1.13 ,0268 -2.30 1.64 .426
h
a For footnotes, see Table XII1.
30-1 -13.1 30-2 -21.0 30-3 -7.70 304 -7.84 30-5 -7.05 30-6 7.66 30-7 7.93 30-8 -7.69 30-9 -6.70 30-10 -6.42 30-11 -7.15 30-12 -6.19 30-13 -6.91 30-14 -12.2 30-15 -7.97 30-16 -6.66 30-17 -9.72 30-18 -9.84 30-19 8.37 30-20 -7.30 30-2 1 -5.42 30-22 -7.03 30-23 -5.71 30-24 1.72 30-25 -2.71 30-26 2.10 30-27 6.38 30-28 2.72 30-29 4.74
Set .961 .964 .931 .940 .925 .974 .983 .973 ,958 .953 .892 .977 .955 .980 .959 .958 .986 .995 .981 .980 .969 .993 .839 ,966 .975 .983 .994 .986 .949
Ra 41.98e 13.00k 26.09e 22.76e 29.58e 136.4e 170.7e 192.2e 72.8Se 53.89e 13.66f 106.2e 46.80e 11.831 17.11’ 22.228 35.8d 46.26’ 38.989 24.35’ 30.99f 111.Of , 7.138’ 27.61f 57.50e 71.67e 115.0f. 34.13’ 36.54e
Fb .297 .801. ,677’ .706k .553k ,107 .221 ,033 .229 .281 .696k .065 .112 .206 .458 .541 .837 S78 .458 .457 .Q17 .458 .602 .514 ,551 ,564 .5 1 1 .850 .578
IC
,506 .663 .330 .306 .328 .242 .245 ,339 .307 .315 .368 .235 .389 .599 ,777 ,704 .467 .309 .498 .443 .437 .254 .597 .0690 ,0818 ,0765 .201 .219 .201
Sest d
1.48e 7.41m 1.22e 1.19e .94se .520e .429e .437e .601e .665e 1.39g .503e .936e 2.56m 2.13; 1.85’ 2.74k 1.17k 1.368 1.23’ 1.22h .695g 3.41m .425h .384e .200e 379 l.llrn .959g
%d Y
Results of Correlations for Amidines and Carboxylic Acids
TABLE XXXl
st
.689g .408e 3.78P 3.38k .521e .127e .7 14g .116e .644e .108e .823e .0827e .92Ig .084ge .49se .0903e .490e .0924e .5 1le .103e .84gg .133e .74se .0836e 1.19e .134e 5.37p ,599’ 7.76m .703g 6.91k .626f 9.10“ .962! 15.5” .307’ 4.97k .45 l g ,4109 5.37O .353e 3.81k .230e 2.53h 8.24m .906p .6 10: .0589e ,644’ .0656e ,687” ,0622’ .186g 2.17k 4.27m .466k .164’ 1.52’
$
9 8 6 5 11
7
7 6 9
5
11 9 13 18 15 25 11 14 10 13 12 4 6 7 5 4 6
5
10
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
149
TABLE XXXII Values of pR for Amidines and Carboxylic Acids
30-1 30-2 30-3 30-4 30-5
20 a
30-6 30-7 30-8 30-9 30-10
49 33 34 34 34
30-11 30-12 30-13 30-14 30-15
46 48
30-16 30-17 30-18 30-19 30-20
14
62
30-21 30-22 30-23 30-24 30-25
63 65 a
54 40
30-26 30-27 30-28 30-29
a (Y and p were not significant for this set. q is a linear function of O R for this set. Correlation was not significant for this set. dp was not significant for this set.
a. Equilibria. Of the sets studied, 21 gave significant correlations with eq.(2). The magnitude of the electrical effect in the case of carboxylic acid ionization is much larger than the magnitude of the electrical effect for amidinium ion ionization. Undoubtedly, the most striking result of the carboxylic acid equilibria correlations is the fact that the composition of the electrical effect appears to be solvent dependent. This phenomenon has been observed for the ionization of 2-substituted benzoic acids (1 90). The carbonyl stretching frequencies of 2-substituted methyl benzoates also show an electrical effect composition which is solvent dependent (10). The rates of reaction of 8-substituted-1-naphthoic acids with diphenyldiazomethane also show a solvent-dependent electrical effect composition (191). Although the results ‘are not conclusive, it seems that systems capable of exhibiting proximity effects may show a solvent dependence of electrical effect composition. The substituted carboxylic acids appear to behave as a system capable of proximity effects. Thus, in water, substituted carboxylic acids show a predominance of the localized effect in most sets, with p~ values of about 34, whereas in cyclohexanol, diphenyl ether, acetone, and benzene, the delocalized effect is strongly predominant, with values of pR of 6 3 to 75. This change in electrical effect with change in solvent results almost entirely from a change in the value of p , which ranges from 3.23 t o 19.1. The NH
II H , O @ + X-C-NH2 26
0 1I
H20+ X-C-OH 28
NH,
‘k
X-C-NH2 27
0
+
H,O
IC + H 3 0 i
X-C-0 29
48 a
48
MARVIN CHARTON
150
NH,
NHZ
’C X-C-NHPh
I X--C=NPh
II G X-C-NHPh
31
30
NH
32
values of 111 range only from 5.42 to 8.37 for those sets for which pR can be calculated. Thus, the range of cr is three units, while the range of 0 is about sixteen. No explanation of these observations is available at the present time. It is not certain from the limited data available how the electrical effect composition depends upon solvent properties. There does not seem to be a dependence upon solvent parameters. It must be noted that the range of UR for the data reported in nonaqueous solvents is very small, amounting to in most cases .12 u unit. Before any conclusions can be definitively drawn, it will be necessary t o study a much wider range of substituent effects. The results obtained are in agreement with the statement that the electrical effect of substituents on the ionization constants of substituted carboxylic acids includes a significant resonance effect. Taft (3) has found that the ionization constants of substituted carboxylic acids are correlated by the u* constants. He has made use of this correlation to define new u* constants and has suggested that these u* constants are a function solely of the “inductive” effect. Our results indicate strongly that this is not the case. We find that these u* constants must be a function of both localized and delocalized effects. This finding is in accord with the suggestion of Swain and Lupton (22) to the effect that u* values contain a contribution from the resonance effect. We do not regard this as significant supporting evidence for this premise, however, as we have already described our reservations concerning the Swain-Lupton treatment. By contrast, the uI constants seem to be a true measure of the localized effect. Because we have proposed that UI constants be defined from 01
= n(pKa, XCH2C02H)t d
(94)
the question is raised of whether uI constants should in fact be defined from the ionization of carboxylic acids. Aside from the empirical observation that such a derivation is in fact successful, that is, u1 constants definitely are in agreement with the values of u1 obtained by other methods, it has been shown previously (19 2) that 01,XCH,
and
Now,
= m i 01,x + C I
(95)
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
151
Then,
(102)
=mq,x+c
It is readily seen that the resonance effect in the CH2X substituent bonded to a carboxyl group is no deterrent to the definition of the 01 constants for X, as uR,XCH, is a linear function of UI, x . From eq. (95) and eq. (IOZ), it is seen that OR, XCH,
= ~ ' u IXCH, ,
+ C'
(103)
Thus, u* values for XCHz groups may be defined free of resonance effects. Values of u* for groups other than XCH2 will contain a resonance effect if they are defined from the ionization constants of carboxylic acids. b. Reaction Rates. All of the six sets studied gave significant correlations with eq.(2). The results obtained are generally in accord with those described above for equilibria. In four of the six sets studied, resonance effects were significant. Values of pR range from 40 to 54. There does not seem to be a clear-cut dependence of the composition of the electrical effect upon solvents. Comparisons are difficult, however, as the data do not refer to the same process in various solvents but are, in most cases, catalytic rate constants.
IV. SUBSTITUENTS ON CARBON-CARBON TRIPLE BONDS
We shall find it convenient to divide the data sets for substituent effects at carbon-carbon triple bonds into three categories; acetylene, ethynylene, and reactions at carbon-carbon triple-bond sets. A. Substituted Acetylene Sets
Data are extant in the literature for five sets of substituted acetylene dipole moments. The correlation of dipole moments with the Hammett equation was discussed in section II.A.l. of this work. The application of the Hammett equation to dipole moments of acetylenes was first reported by Charton (18). The sets studied here are reported in Table XXXIII. Results of the correlations are presented in Table XXXIV, and values of pR are set forth in Table X X X V .
VI w
c.
33-1 33-2 33-3 334 33-5 33-6 33-7 33-8 33-9 33-10 33-11 33-12 33-13 33-14 33-15 33-16 33-17 33-18 33-19 33-20 33-2 1 33-22 33-23 33-24 33-25 33-26 33-27 33-28 33-29
Set
VCH A v / v g . lo’
AV
vC H ”C H VCH assoc
lu
kr kr
kr
P P Lc P P
Q
. 3,
3-Substituted propiolic acids 3 ” ethyl propiolates 2 ” phenyl acetylenes
9, ’
Substituted acetylenes 2- ” phenylacetylenes 1- ” 1-hexynes 1 ” 1-heptynes 3 ” propiolnitriles Substituted acetylenes H-D exchange ” H-D ” ” H-D ” ” H-T ” Substituted acetylenes
Substrate
p-cumene
PrBu CCI, CS 2 Dioxane Bu,O MeAc DMF Pyridine Et,N
DMA
90% v/v MeAc-H,O 88.5% v/v MeOH-H,O DMF 5 M D,O (1 : 4) v/v MeOH-H,O PI* Et,O
Solvent
Carbon-Carbon Triple-Bond Sets
TABLE XXXIII
OHC-Me-N-Ph-sydnone
Et, N
Reagent
25 25 140
21 21 40 25
YC
193 193 193 193 193-5 196 196 197 198 199 199 199 200 200 201,202 201,202 201,202 201,202 201,202 201,202 20 1 20 1 201 196 203 203 18,204,207 18 205
Ref.
a
33-1 33-2 33-3 33-4 33-5 33-6 33-7 33-8 33-9 33-10 33-1 1 33-12 33-1 3 33-14 33-15 33-16 33-17 33-18 33-19 33-20 33-21 33-22 33-23 33-24 33-25 33-26 33-27-1 33-21-2 33-28 33-29
Set
4.97 8.24 7.03 7.00 -.784 4.41 3.46 7.26 6.55 -47.8 -60.8 -78.6 -34.7 50.4 2.11 -.590 -.683 20.9 35.7 11.2 8.40 60.9 14.0 -1.31 4.08 3.48 2.22 2.07 2.95 6.18
P -.I05 -.419 -.982 -.967 3.99 2.37 .909 1.22 2.08 3315. 331 1. 3255. 3311. 82.9 3.53 4.03 5.62 20.1 20.4 18.9 28.7 35.5 37.0 -2.30 2.02 2.22 .801 .749 .390 1.13
h
For footnotes, see Table XIII.
4.63 5.98 7.86 7.87 .316 6.86 7.74 12.3 5.59 -.791 11.8 -74.3 -4.27 97.1 4.39 6.01 8.00 36.3 38.6 25.8 31.3 72.5 52.3 -.335 .328 1.02 1.82 1.86 2.59 -.214
OL
.928 .964 .989 .990 .273 .9991 .990 .694 .969 .989 .910 .981 .98 1 .991 .888 .928 .949 .990 .991 .993 .962 .930 .902 .367 .883 .929 .959 .994 .966 .99 1
Ra
286.8'. 5 1.88' .9301 61.75e 89.08e 23.91' 31.77g 77.05e 135.0e , 7.438' 12.43: 17.95' 96.30e 106Se 148.4e. 18.57'. 9.674' 6.512k .702l. 8.874' 12.56' 39.61e 261 .2e 6.986l 56.04'
.040'
18.59f 19.64: 44.69: 48.82'
Fb
.836
.1lh
.I57 .147 .188 .188 .864 .434 .595 .910k .Ol 1 .156 .870k .870k .283 .009 .534 .534 .5 34 .534 .534 .534 .354 ,354 .354 .I27 .635 ,676 .413 ,396
.65 1 .630 .388 .371 .821 .0755 .197 1.13 .204 1.92 1.88 4.82 1.49 2.70 .626 .572 .636 1.47 1.64 .864 1.11 3.56 3.12 .514 .334 .291 .137 .05 34 .332 .159
d sest d
.871g 1.24h .889h .850h 4.3lP .3011 .762g 10.5" .613e 6.1lP 12.5" 32.1m 2.67m 7.05e 1.52' 1.39h 1.54g 3.58e 3.99e 2.10e 5.2eg 16.9: 14.8' 1.21' .836O .798" .214e .0837e .882" .836O
SOL
Results of Correlations for CarbonCarbon Triple-Bond Sets
TABLE XXXIV
1.12'
1.51:
1.3lg 2.301 1.42; 1.36' 1OSp , .267J .637' 5.36" l.OSe 3.63e 14.5' 37.1m 3.06e 5.69e .627O 3.08p 3.43p 7.94k 8.82h 4.65g 7.87" 25.4k 22.2' 1.11: 1.37' 1.28k .379e .150e
.340° S12" .381" .364" .721m .0747j .183' .569m .113e 1.41e 2.32e 5.96e .776e 1.42e .504g .461e .512e 1.69e 1.32e .696e .890e 2.87g 2.51e .240e .166g .171e .0513e .0217e .177" .126h
d Sh
6 6 9 8 7 7 7 7 7 7 6 6 6 12 8 7 10 9 4 5
1
4 4 5 5 11
5
9 6 5
n"
MARVIN CHARTON
154
TABLE XXXV Values of pR for Carbon-Carbon Triple-Bond Sets Set
pR
Set
pR
Set
33-1 33-2 33-3 33-4 33-5 33-6
52 54 47 47
33-7 33-8 33-9 33-10 33-11 33-12
31
33-13 33-14 33-15 33-16 33-17 33-18
a
39
9
54
pR
Set
pR
Set
PR
48 40
3d4
33-19 33-20 33-21 33-22 33-23 33-24
33-25 33-26 33-27 33-28 33-29
53
37
46
a
a
a Correlation was not significant for this set.
was not significant for this set. a and p were not significant for this set. d B was not significant for this set. 01
Of the five sets which were correlated with eq.(2), four gave significant correlations. Values of PR are in the range 50 to 54, which indicates approximately equal contributions of the localized and delocalized effects. Thus, dipole moments of substituted acetylenes could be correlated successfully with the up constants. The data available are insufficient to provide a significant test of the validity of eqs. (21) and (22). The range of uI for the constant substituent attached to the triple bond is only .14 (I unit, and the range of uR is .11 u unit. The magnitude of the localized electrical effect in the case of the substituted ethylenes is the same as that of the substituted acetylenes. The latter are significantly more susceptible to resonance effects than are the former, however.
B. Ethynylene Sets We find that it will be useful to divide the ethynylene sets into two categories: sets involving properties of the ethynyl proton in substituted acetylenes, and the other ethynylene sets.
1. Properties of the Ethynyl Proton Hydrogen-deuterium and hydrogen-tritium exchange involving the ethynyl proton in substituted acetylenes has received some attention. Rates of hydrogen-deuterium exchange have been reported to be a linear function of (I* values (197,206), as have also rates of hydrogen-tritium exchange (198). Data for three sets of rates of hydrogen-deuterium exchange and one set of rates of hydrogen-tritium exchange have been correlated with eq. (2). The sets studied are set forth in Table XXXIII. Results of the correlations are presented in
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
155
Table XXXIV, values of PR are given in Table XXXV. Of the three sets of hydrogen-deuterium exchange rates, two gave significant correlations with eq. (2), as did also the hydrogen-tritium exchange rates. In contrast to the conclusions of Dessy, Okuzumi, and Chen (197), we find there are significant resonance effects on both the hydrogen-deuterium and the hydrogen-tritium exchange rates, with PR for the former ranging from 31 to 39 and pR for the latter having a value of 54.The magnitude of the localized electrical effect for the substituted acetylenes was in the range 5.6 to 7.7. This range may be compared with a value of 12.5 obtained for partial rate factors at the ortho position of substituted benzenes undergoing hydrogen-deuterium exchange. The large difference in the magnitude of the electrical effect between orthosubstituted benzenes and substituted acetylenes may result, at least in part, from the difference in medium, the ortho-substituted benzene data having been obtained in liquid ammonia. It seems likely, however, that the greater part of the difference is a result of the difference in geometry between the two systems. In the ortho-substituted benzenes, the substituent and the proton undergoing exchange are adjacent to each other, separated only by a small amount of empty space. In the case of the substituted acetylenes, the substituent and the proton undergoing exchange are separated by the carbon atoms of the ethynylene group. Several sets of data involving the C-H stretching frequency of substituted acetylenes are available in the literature. The sets studied are reported in Table XXXIII, results of the correlations are given in Table XXXIV, and values of pR are set forth in Table XXXV. Of the four sets of v values and the one set of Av values, all gave significant correlations with eq. (2). In the majority of the sets studied, the delocalized effect was predominant, in spite of the fact that no overlap between the sigma bond to the ethynyl proton and the n orbitals of the ethynylene group is possible. This result tends to support the findings in the rates of hydrogen-deuterium and hydrogen-tritium exchange that resonance effects are of real importance. Nine sets of data involving the quantity ( A u ) / v C H % for substituted acetylenes have been correlated with eq. (2). In these data, Av is the difference between v ~ ~ , ~and , , U, C H , ~ All . nine sets gave significant correlations. The meaning of these results is obscure, however, as the quantity Av/uCH,g may not be a simple function of substituent constants. Three sets of nmr chemical shifts for the ethynyl proton have been correlated with eq. (2). Of these sets, two gave significant correlations with eq. ( 2 ) . Nevertheless, as the most extensive collection of substituents is included in the set which did not give significant correlation, it seems likely that chemical shifts of ethynyl protons are not correlated by the extended Hammett equation. This behavior contrasts with that of chemical shifts for trans- and cis-vinyl protons and is in agreement with the behavior of geminal vinyl protons.
156
MARVIN CHARTON
2. Other Ethynylene Sets Data are extant in the literature for two other sets of ethynylene compounds. The sets studied are reported in Table XXXIII. Results of correlation are set forth in Table XXXIV and values of pR in Table XXXV. The ionization constants of 3-substituted propiolic acids, which were first correlated with the Hammett equation by Charton (18), gave an excellent correlation with eq. (2) (set 22-27-1). The results are very much improved by the elimination of the value for X = H (set 33-27-2). The composition of the electrical effect corresponds approximately to that of the up constants. The magnitude of the electrical effect is significantly less than that observed for the trans-3-substituted acrylic acids. The rates of hydrolysis of 3-substituted ethyl propiolates did not give a significant correlation with eq. (2). In view of the fact that the set contained only four points, this result is hardly surprising. It seems likely that if more points were available, a good correlation would have been obtained. The paucity of data for substituted ethynylene sets is remarkable. Before any definitive conclusions concerning the transmission of substituent effects by the triple bond can be made, much further investigation is required. This field is one which is certainly worthy of further inquiry.
C. Reactions of Carbon-Carbon Triple Bonds There are almost no studies of substituent effects on additions to carbon-carbon triple bonds extant in the literature. Bowden and Price (208) have reported a correlation of rates of addition of hydrogen bromide to 3-substituted propiolic acids with the Hammett equation using the up constants. Unfortunately, there are only three substituents in the set. Sufficient data are available for a single set of 1,3-dipolar cycloaddition. The set studied is shown in Table XXXIII, and the results of the correlation are in Table XXXIV. The correlation was significant; the delocalized effect is predominant in this set. Once again, there is a remarkable lack of quantitative data on addition reactions of substituted acetylenes. This area is one which certainly merits investigation.
V. SUBSTITUENTS ON CARBON-HETEROATOM TRIPLE BONDS There is only one type of compound in this category, substituted nitriles. It will be useful to divide the data sets for substituent effects at carbon-heteroatom triple bonds into two classes, substituted nitriles and heteroethynylene sets.
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
157
A. Substituted Nitriles Dipole moments of substituted nitriles were correlated with the u* constants by Taft3 and with the up constants by Charton (18). In addition to dipole moment data, some information is available on the CZN stretching frequencies of substituted nitriles. The sets studied are reported in Table XXXVI. Results of the correlations with eq. (2) are given in Table XXXVII, and values of pR are set forth in Table XXXVIII. The correlation of the dipole moments of substituted nitriles with eq. (2) gave significant results, which were very much improved by the exclusion of the value for X = I (set 36-1-2). In contrast t o the results obtained for substituted ethylenes, acetylenes, and benzenes, the value of p obtained for dipole moments of substituted nitriles is not significant. The value of a obtained for the substituted nitriles is comparable to the value of a observed for the substituted acetylenes. TABLE XXXVI Substituted Nitrile and Heteroethynylene Sets Set
Q
Substrate
36-1 36-2 36-3 364 36-5 36-6 36-7 36-8 36-9 36-10 36-1 1 36-12 36-1 3
cc
Substituted nitriles
Solvent
Reagent T"C
VCN
PhOH MeOH
A'OH
Av
ICl
Ke Ke Ke Ke
0 10 25 40
Ref. 193 209 209 209 209 209 210 210 211 212 212 212 212
Thomas and Orville-Thomas (209) report a linear correlation of the , ~ ~ )the Taft u* constants. Their data have been quantity ( V C N , X - U ~ ~ with correlated with eq. (2). Of the five sets studied (sets 36-2 through 36-6), three gave significant results. The value of 0 for these sets is not significant.
B. Heteroethynylene Sets Caldow and Thompson (213) have reported a correlation of Av with the Taft u* constants for hydrogen bonding between phenylacetylene and substituted
m
VI c
36-1-1 36-1-2 36-2 36-3 364 36-5 36-6 36-7 36-8 36-9 36-10 36-1 1 36-12 36-13
Set
a
-2.72 -2.92 24.0 310. 189. 193. 191. -148. -177. -61.9 .730 '11.70 2.80 1.00
d h
3.52 3.45 2286. 2278. 2265. 2266. 2266. 145. 59.1 149. 1.17 1.12 1.07 .625
For footnotes, see Table XIII.
-3.92 -4.27 -83.1 -55.2 -116. -117. -118. -169. -14.0 -133. -3.45 -3.54 -3.89 -3.22
a
.788 .867 .988 .980 385 .879 389 .963 .928 .990 .9997 .998 ,998 .997
Ra
6.548i 10.64g 60.10' 36.91' 7.226' 6.775k 7.541' 94.75e 27.71:' 48.55' 966.2' 161.4k 132.6k 87.15k
Fb
d
Sest
.847 .711 5.61 S10 6.90 .427 20.6 .427 21.5 .427 20.4 .091 9.38 .510 , 3.99 .927k 4.98 .875 .0271 .875 .0644 .875 .0742 .875 .0826
.295 .300 .510
rc 1.09g .93Ig 14.3 17.5. 41.6' 43.4k 43.23j 12.6e 19.7g 32.1k .155j .370k .426k .474k
d sa
Results of Correlations for Carbon-Heteroatom Triple-Bond Sets
TABLE XXXVII
1.89" 1.59m 47.8 58.8 167." 174." 165." 33.8e 49.2g 122.' .689" 1.64' 1.89" 2.10'
spd
.398e .336e 5.79 7.12 20.1e 20.9e 19.9e 3.79e 5.49e 12.8g .0664j .158k .182m .202m
d Sh
5 4 4 4 4
10 6 6 7 7 7 18 12
11
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 159
nitriles. Allerhand and Schleyer (210) have found a correlation of Au with u* for hydrogen bonding between substituted nitriles and phenol or methanol. Three sets of data are extant in the literature involving hydrogen bonding to substituted nitriles. The sets studied are set forth in Table XXXVI, results of correlations are in Table XXXVII, and values of pR are given in Table XXXVIII. TABLE XXXVIII Values of pR for Carbon-HeteroatornTriple-Bond Sets ~
Set
pR
Set
pR
Set
36-1 36-2 36-3 36-4
a
36-5 36-6 36-7 36-8
a a
36-9 36-10 36-11 36-12
a
47 71
pR
Set
pR
36-13
a
a
a a
a p was not significant for this set.
Correlation was not significant for this set. 01 is a linear function o f OR for this set.
Although all three sets gave significant correlations with eq. (2), set 36-9 shows a linear relationship between uI and UR and therefore is of no use in a determination of either the magnitude or the composition of the electrical effect. The remaining sets show widely disparate values of p ~ hydrogen : bonding with phenol gives a value of 47, whereas hydrogen bonding with methanol gives a value of 71. No reason for this discrepancy is known. The magnitude of a is also very different for the two reagents, the phenol set giving a value about twice, that of the methanol set. In any event, it seems clear from the results that resonance effects are important in hydrogen bonding to substituted nitriles. This result is in accord with those obtained for hydrogen-deuterium and hydrogen-tritium exchange in substituted acetylenes, to which hydrogen bonding in substituted nitriles may be compared, as the probable site of the hydrogen bonding is the full nonbonding orbital on the nitrogen atom. Person, Golton, and Popov (212) have found correlations between log Ke for complex formation between substituted nitriles and halogens and the Taft u* constants. The correlation of the substituted nitrile-iodine complex equilibrium constant with u* values has been questioned by Maguire, Bromley, and Banewicz (214). The data of Person, Golton, and Popov for complexes of substituted nitriles with IC1 were correlated with eq. (2). The results are presented in Table XXXVII. All four sets gave significant correlations. The value of was not significant for these sets. This result may not be meaningful, however, as the range of uR in the sets is only .1 u unit. Thus, it is not possible to draw any conclusions as to the composition of the electrical effect in these complexes.
160
MARVIN CHARTON
VI. SUBSTITUENTS ON CYCLOPROPANE RINGS Data for substituted cyclopropane rings can be conveniently arranged in five categories: substituted cyclopropane sets, cyclopropylidene sets, trans-cyclopropylene sets, cis-cyclopropylene sets, and reactions of cyclopropane rings. The correlation of data for cyclopropanes with the Hammett equation (19) and the extended Hammett equation (2 15) has been reported by Charton. A. Substituted Cyclopropane Sets
The sets studied are set forth in Table XXXIX. Results of correlations are reported in Table XL and values of PR in Table XLI. The dipole moments of substituted cyclopropanes gave a significant correlation with eq. (2). The value of PR obtained is in agreement with the values previously found for substituted vinyl compounds (section II.A.l.) and for substituted benzenes (for which a value of PR of 39 is observed). Compounds of the type RX, where R is Me, Et, i-Pr, or t-Bu, show an average value of pR of 29 (220). The results clearly demonstrate the increased resonance interaction between cyclopropyl ring and substituent as compared with an ordinary alkyl group, the former behaving in a manner like that of the vinyl and phenyl groups. The substituted acetylenes show a somewhat higher value of pR than do the cyclopropanes, substituted vinyl compounds, or substituted ethylenes, with an average value of pR of 50. The value of (Y observed for the substituted cyclopropane dipole moments is comparable to that observed for substituted ethylenes, benzenes, and acetylenes. The ionization potentials of substituted cyclopropanes also show a significant correlation with eq. (2). The value of pR obtained is comparable to that observed for substituted ethylenes and 1-substituted propenes (section II.A.2.) and is considerably above that found for substituted benzenes (for which a value of pR = 59 is obtained). This result confirms the existence of a large resonance interaction between the cyclopropane ring and substituents. The magnitude of (Y is considerably greater for substituted cyclopropanes than it is for substituted ethylenes or benzenes. Five sets of data for the near infrared absorption of substituted cyclopropanes are extant. This type of data was first correlated with the (I* constants by Gassman (221). Charton correlated this set of data with the 01, (I, and up constants and found that the up constants gave the best results. In a further study, including a wider range of substituents, Gassman and Zalar (222) reported that the best correlation was with u*. Using their data for substituted cyclopropanes and trans-1 -substituted 2-phenylcyclopropanes (sets 39-3-1 and 39-6-1) the values of p that one obtains are indeed not significant. On the exclusion of the amino group, the substituted cyclopropanes show a linear relationship between uI and U R and therefore the composition of the electrical
”
p
kr
kr
”
”
39-1 39-2 39-3 39-4 39-5 39-6 39-1 39-8 39-9 39-10
39-1 1
39-12 39-13
39-14
pKa pKa
”
A, n u
I
Q
Set
Solvent
nuns-1-Substituted 2-phenylcyclopropanes ” 1 ” 2,2dimethylcyclopropanes ” 1 ” I-cyclopropane carboxylic acids HZO ” 2 ” 1 ” 2 ” 3,3-dimethyl-lcyclopropane carboxylic ” acids ” 2,3disubstituted cyclopropylmethyl-3, Sdinitrobenzoates ” 2-Substituted-1-bromocyclopropanes cis-2-Substituted-3,3dimethyl-l-cyclopropane carboxylic acids ” 2 ” 1-bromocyclopropanes
Substituted cyclopropanes
Substrate
Cyclopropane Sets
TABLE XXXIX
50%EtOH-H20
130
130 25
100 50%EtOH-HzO Cellosolve-H,O
15 Cellosolve-H,O 60%MeAc-HzO
25 25
219
219 61
218
19,215 215 216 211 211 216 216 19 19,215 19
T C Ref.
80%Methyl
Reagent
h)
m
w
a
39-1 39-2 39-3-1 39-3-2 39-4 39-5 39-6-1 39-6-2 39-7 39-8 39-9 39-10 39-11 39-12 39-13 39-14
Set
h
3.95 .419 2.95 10.26 .000965 1.637 -.0162 1.636 -.00938 1.637 .0176 2.230 -.000225 1.635 -.0166 1.635 -.0158 1.644 -5.47 4.91 -.828 4.69 -1.55 7.56 -7.45 .632 -14.1 -1.56 - .84 1 8.09 -21.0 -1.33
P
For footnotes, see Table XIII.
4.96 1.19 -.0278 -.0204 -.0219 -.0276 -.0181 -.0139 -.0187 -6.38 - 1.94 -3.19 -3.06 .4.62 -.990 3.93
a
Fb
.981 39.10g .999 218.5' .957 54.8Se .985 143.7e .950 18.47g .969 38.28' .945 20.87f .996 2g2.pe .99994 4142.' .999 240.8' .975 48.24:: .995 93.82' .9999993 333333.f .9994 434.5' .865 1.485' .980 11.87'
Ra .113 .071 .477 .773g .646 .594 SO8 .615 .753 .689 .071 .407 .755 .064 .918 .064
rc
d
SlY
d
Sl3
.l .27k .350 .578g. .0483 .0869' ,204 .00181 .00296e .00242O .00263e .00115 .00456' .00558h .00934" .00192 .00117 .00323 .00507 .00146 .00329g .00211p .000401 .00106e .O022Sg .00088d .000132 .000413h .488k .111 ,298' .208e .0874 .217h .1 78h .0918 .242g .00213 .0146g .O1loe .486 .629 .0655 581" 1.03O .0882 4.32m 5.59O .582
Ser t
d
Results of Correlationsfor Cyclopropane Sets
TABLE XL
.233m .O36Og .000791e .00051e .00158e .000914 .00108e .00029Se .000103e .075Sg .0362e .0471e .00249' .0589 .0706g 524"
d Sh
4 4 4 4
5
6 4 13 12 7 8 8 7 4 4 8
nq
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 163 TABLE XLi Values of pR for Cyclopropane Sets Set
pR
Set
39-1 39-2 39-3-2
44 71
394 39-5 39-6-2
a
pR
Set
pR
Set
pR
Set
46 46 30
39-10 39-11 39-12
33 71
39-13 39-14
54
39-7 39-8 39-9
pR
a U I is a function of OR for this set.
b p was not significant for this set. Correlation was not significant for this set.
effect cannot be determined (set 39-3-2). The trans-1-substituted 2-phenylcyclopropanes, however, on exclusion of the amino group, show a significant value of 0 (set 39-6-2). The 2,2-dimethyl-l -substituted cyclopropanes also show a significant value of 0 (set 39-7). On the other hand, the substituted cyclopropane data of Weitkamp and Korte (217) do not give a significant value of 0. We are forced to conclude from these results that the composition of the electrical effect in these data remain open to question and that further investigation is required. B. Cyclopropylidene Sets
Only one set of data is available in this system, and it has only four points. Although significant correlation is obtained, the results can in no way be considered conclusive. It is fascinating to note that the value of pR for this set is 46, which corresponds approximately to the P R value of the up constants. An explanation for this composition of the electrical effect has been proposed by Charton (19). It is obvious that this system is in need of further investigation.
C. trans-CyclopropyleneSets Data are extant in the literature for four trans-cyclopropylene sets. Of these, two are disubstituted (sets 39-9 and 39-1 1). Positions trans-2 and trans-3 are completely equivalent in cyclopropanes bearing the reaction site at position 1. These sets have been correlated with eq. (30). The other two sets have been correlated with eq. (2). Three of the four sets studied gave significant correlations. The fourth set had only four points. The results obtained clearly show a significant resonance effect. They clearly demonstrate that the trans-cyclopropylene system does involve a resonance interaction between the substituent and the cyclopropane group. The trans-cyclopropylene system again
164
MARVIN CHARTON
is one which will require further investigation, although the general outline of its behavior seems clear.
D. cis-Cyclopropylene Sets Only two sets of cis-cyclopropylene data are extant in the literature, and each set has only four points. It is therefore not surprising that neither set gives a significant correlation with eq. (2). This system is obviously in great need of further study to ascertain the presence or absence of steric effects and the magnitude and composition of the electrical effect.
E. Reactions of Cyclopropane Rings Only one set of data for the addition of bromine to substituted cyclopropanes has been reported (223). In this set, the substituents are of the type XCHz, and therefore the data were correlated by Charton with the oI constants. Once again, this area requires extensive investigation.
VII. SUBSTITUENTS ON HETEROCYCLOPROPANE RINGS In conformity with our previous approach, we classify substituent effects on heterocyclopropane rings into four categories. They are substituted heterocyclopropyl sets, heterocyclopropylidene sets, heterocyclopropylene sets and heterocyclopropanes with heteroatom reaction sites. A. Substituted Heterocyclopropyl Sets There are unfortunately no data extant in the literature for substituted heterocyclopropyl sets. B. Heterocyclopropylidene Sets Again, there are no data for heterocyclopropylidene sets extant in the literature. It would be of great interest to have such data available. C. Heterocyclopropylene Sets Once more, no data are extant in the literature for heterocyclopropylene sets. This area certainly merits investigation, as it would be interesting and instructive to be able to compare substituent effects on the heterocyclopropane ring with those on the cyclopropane ring and the heterovinylene group.
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
165
D. Heterocyclopropanes With Heteroatom Reaction Sites There are two sets of data extant in the literature for this system. The sets studied are shown in Table XLII. Results of correlations with eq. (2) are given in Table XLIII. Values of PR are described in Table XLIV. Barely significant results were obtained for both sets. Undoubtedly, the results would have been better had more data been available. Regrettably, no conclusions can be based on such limited evidence. This system requires further work. TABLE XLII Heterocyclopropane Sets Set
Q
Substrate
Solvent
Reagent T"C
42-1 42-2
AVOH
Substituted oxiranes
tetrachloroethylene
PhOH
Ke
TABLE XLIII Results of Correlations for Heterocyclopropane Sets
P
Set
a
42-1 42-2
-1.77 -1.31
Set
42-1 42-2
h
Ra
188. .975 -177. .451 .973 -1.85
Sest d
6.94 .0594
sa d
sad
Fb
18.90k .738 17.61k .738
sf
132." 16.1g 58.1k .0497m 1.12" .138k
TABLE XLIV Values of pR Set
PR
Set
PR
42-1
a
42-2
b
a
rc
p was not significant for this set. a and p were not significant for this set.
nq
5 5
20 20
Ref.
224 224
166
MARVIN CHARTON
VIII. SUBSTITUENTS ON OTHER UNSATURATED SYSTEMS It will be convenient to consider under one heading all those unsaturated systems which do not fall under any of the sections previously discussed. There are four categories which are included in this catch-all heading. They are pyridones, quinones, multiple substitution at nonequivalent sites, allenes and cumulenes, and conjugated dienes and polyenes.
A. Pyridones Pyridones have not been considered previously because the reaction site can undergo resonance effects involving more than one type of interaction. Localized effects, assuming they are field effects, will not be affected. If the localized effect were an inductive effect, which seems very unlikely, then there would be two paths to the reaction site, Consider the pyridones for which data are available. Three sets are extant. They are the 3-substituted 4-pyridones, 33; the 5-substituted 2-pyridones, 34; and the 3-substituted 2-pyridones, 35. In each of these systems, the substituent is conjugated with the nitrogen atom by one path and in
33
34
35
a vinylidene position by the other. It is therefore impossible to assign these compounds to any of the categories previously described. The results of the correlations are set forth in Table XLVI, and values of P R are given in Table XLVII. Significant correlations were obtained for all three sets. The results show a predominance of the localized effect, as is shown by the p R values. From previous results for trans-vinylene systems, if the influence of the enone moiety in 33 and 34 could be ignored, it would be predicted that pR values in the neighborhood of 50 might be found. Obviously, then, the pyridone structure as a whole must exert an influence on the resonance effect observed in these compounds (again assuming that the localized effect is represented only by a field effect).
B. Quinones When substituted quinones undergo reaction at the carbonyl groups, the substituent does not exert the same effect on each carbonyl group, Consider, for
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 167
example, the 3-substituted 1,2-benzoquinones, 36; the 4-substituted 1,2-benzoquinones, 37; and the 2-substituted 1,4-benzoquinones, 38. In 36, the substituent is in a vinylidene
b'.
&I
+x0
X
36
37
38
position with respect to one carbonyl group and a divinylene position with respect to the other. In 37, the substituent is in a vinylidene-vinylene position with respect to one carbonyl group and a vinylene position with regard to the other. In 38, however, the substituent is in a vinylidene position with respect to one carbonyl group and a vinylene position with respect to the other. As a result of this, quinone carbonyl group reactions and properties do not fit into any of the categories previously examined. We have therefore chosen to examine them here. The largest category of data which falls into this classification is that of quinone oxidation-reduction potentials. The application of the Hammett equation to quinone oxidation-reduction potentials was first studied in some detail by Charton (248). The subject has since been treated in depth by Zuman (249,250). Horner and Geyer (238) have found a linear relationship between both up and up values and the oxidation-reduction potentials of 4-substituted 1,2-benzoquinones. It is then taken up again here because no previous attempt has been made to correlate the data with eq. (2) or with eq. (30). The sets studied are given in Table XLV. Results of correlation are reported in Table XLVI and values of PR in Table XLVII. Of the 45 sets of quinones and quinonediimines studied, 3 1 gave significant correlations. Of the fourteen sets which did not give correlation, twelve had only four points. The remaining two sets had five points. Thus, had sufficient data been available, the results undoubtedly would have been much improved. The Eo values for 2-substituted 1,6benzoquinones (sets 45-4 through 45-7, 45-10) show an average value of PR of 59. Thus the resonance effect predominates. For most of these sets, the up constants are not the best parameters for correlation. By contrast, the electron reduction potentials (set 45-8) show a PR value of 39, which indicates predominance of the localized effect. The 2,s-disubstituted 1,4-benzoquinones differ distinctly in their behavior from the 2-substituted 1,4-benzoquinones in that they show an average PR value of 53. The one-electron reduction potentials of these compounds show about the same composition of the electrical effect, with a value of pR of 50. The only set of Eo values available for the 2,6-disubstituted 1,4-benzoquinones gave a PR value of 51, comparable to the values observed for the 2,s-disubstituted 1,Cbenzoquinones. The 2,3,5,64etrasubstituted 1,4-benzoquinones have
K 00
45 -2 3 45-24
45-1 45-2 45-3 45 4 45-5 45-6 45-1 45-8 45-9 45-10 45-1 1 45-12 45-1 3 45-14 45-15 45-16 45-11 45-1 8 45-19 45-20 45-21 45 -22
Set
Q
H2O
75% EtOH-H,O, 95%EtOH-H,O, 1 1 AcOH-H,O MeCN
PhH H2O 95% EtOH-H,O, 95% EtOH-H20, MeCN PhH
0.2 M HCl 0.1 N HC1 1.0 N HCI AcOH-H,O MeCN
H,O
3-Substituted 4-pyridones 5 ” 2 3 ” 2 ” 2 ” 1,4-benzoquinones ” 1,4 2 *’ 1,4 2 2 ” 1,4 2 ” 1,4 2 ” 1,4 2 ” 1,4 2,5-Disubstituted 1,4-benzoquinones 2,s ” 1,4 ” 1,4 2,5 2,5 ” 1,4 ” 1,4 2,5 ” 1,4 2,6 2,3,5,6-Tetrasubstituted1,4-benzoquinones 2,3,5,6 1,4 1,4 2,3,5,6 2,336 1,4 2,3,5,6 1,4 N4,N4-Dimethyl-2-substituted 1,4-benzoquinone diiminium perchlora tes N‘ ,N4-Diethyl-3-substituted 1,4-benzoquinone diiminium ions N’,N’ ” 2 ” 1,4 ))
Solvent
Substrate
Other Unsaturated System Sets
TABLE XLV
20 20 20 25 25 25 20 25 25 25 25 0.5 N HCl 25 25 1 N HCI 15 25 25 0.1 N NaOH 25 1.0 N HCl 25 20 25 25
T“C
237 231
13 13 13 225 226,221 226,221 228,229 230 230 231-3 234 226,227 226,221 230, 235 231-3 231-3 230 226,221 228 230 230 236
Ref.
c
\o
m
45-25 45-26 45-21 45-28 45-29 45-30 45-31 45-32 45-33 45-34 45-35 45-36 45-31 45-38 45-39 45-40 4541 4542 45-43 45-44 45-45 45-46 45-41 4548 45-49 45-50 45-51 45-52 45-53
E,
vCO pKa pKa pKa
uco
E‘ Eo
Eo Eo Eo
E,
E,
E,, E,:,
E,.$
E,, E, E,
E, E,.,
E, E,
E,
E, EA
E, E, E,
3-Substituted 1,2-benzoquinones 6 ” 3-methoxy-l,2-benzoquinones 3 ” 4,Sdimethyl 3,6-Disubstituted 1,2-benzoquinones 4-Substituted 1,2 ” 1,2 4 5 ” 3-methoxy-l,2-benzoquinones 4,s-Disubstituted 1,2-benzoquinones ” 192 3,4 3,4,5,6-Tetrasubstituted1,2-benzoquinones 2-Substituted 1,4-naphthoquinones ” 1,4 2 ” 1,4 2 2 ” 1,4 2Chloro-3-substituted 1,4-napthoquinones ” 1,4 2 ” 3 2-HY~IOXY-3-” 1,4 4-Substituted 1,2-naphthoquinones 4 ” 1,2 3,3’-Disubstituted-Diphenoquinonediimines 3,3‘ 3,3‘ 3,3’ 3,3’ 3,5,3’,5’, Tetrasubstituted diphenoquinones 2-Substituted 1,4-naphthoquinones Disubstituted oximes (X,C=NOH) Disubstituted dioximes [ (XC=NOH],] truns,trans-5-Substituted 2,4-pentadienoic acids CHCl, CCl, H2 0
H, 0 50% MeAc-H,O 6 N H,SO,
1-10 EtOH-H,O
H, 0
25 25
25 25 0 25 40
4cr
50% EtOH-H,O, 0.1 N HC1 EtOH-H,O, 0.1-0.2 N HCl 25
PhH H, 0
25 25 25 25 25 25 25 25 25 25
238 238 238 238 238 239 238 238 238 238 240 240 24 1 242 240 240 240 243 243 244 244 244 244 244 245 246 13 13 15,241
z
45-5 45-6 45-7 45-8 45-9 45-10 45-1 1 45-12 45-1 3 45-14 45-15 45-16 45-17 45-18 45-19 45-20 45-21 45-22 45-23 45-24 45-25
54-4
45-1 45-2 45-3
Set
-.185 . I 15
.I05
-5.91 -4.89 -4.54 .211 .166 .I66 .271 .545 .235 .197 .172 .248 .211 .604 .I89 .I 36 .341 .178 .213 .522 .448 .340
OL
4.68 -2.53 -2.95 .358 .222 .222 .452 .348 -.447 .222 .190 .287 .332 .612 .I99 .I42 .488 .308 .395 .345 .332 .271, -.226 -.00908 .I45
P 10.48 11.58 11.85 .699 .690 .686 .700 -.5 1 I -1 .I 3 .696 .652 .644 .699 --.464 .683 .683 -.312 .681 .703 -.551 -1.18 .235 -.226 -.291 .783
h
1 .ooo .99 1 .990 .985 .9997 .98 1 .980 .9999 .999 .997 .990 .960 .959 .994 .986 .995 .987 .992 .999 .726 .415 .95 1
.9993 .998 .997
Ra
363.1J 392.7e 180.1' 25907.f 54.583 48.51: 32.201 783.1' 12.82' 71.93e 4430.e, 291.1' 266.1e, 46.93' 23.811: 17.27' 43.54: 36.22j 46.26' 54.66f 88.0Sf 184.9k 4.446k .208' 9.507k
Fb .591 .050 .059 .859 .405 .405 .793 .819 ,819 .377 .991 .244 .620 .757 .687 .374 .702 .769 .818 .590 .590 359 .286 .464 .487
IC
.lo6 .116 .162 .000247 .0920 .0104 .00926 .00444 .0324 .0115 .00119 .00896 .0110 .0426 .0233 .0242 .0438 .0348 .0209 .0990 .0662 .00400 .07 14 .0805 .0130
Sest
d
Results of Correlations for Other Unsaturated Systems
TABLE XLVI
.0343e .0161" .0143" .310° .030Sk
.0513'
.0673h .027Sg .025Sh .0366k .039dk .0221
.0155' .O 14ge
.361' .181e .254g .000994' .022Oh .0233h .0347h .O 1 9 d .129" .0210e .O 1OSg
d
sfl
.0853' .0570h .0410k .0759' .148p .0386k
.OSllk
'
2.44" .40@ S58' .00254g .0230h .0244h .089 I .0456k .332" .0212e .048Ok .0134J .014ee .139' .0387g .0328' .0774m .0363'
.105g .0868e . I 22e .000246' .00720e .00763e .00889e .00424g .0309' .00638e .01 26e .01 16h .0072Se .0279' .01 39e .0177e .0438k .0273g .0209' .07 I Og .0474e .0398h .0374e .0583' .00984'
d
Sh
4 6 6 4 11 5 5
5
7 6 4
5
4 4 9 5 4 6
5 5 5
4 6 5 4
nq
2
45-26 45-27 45-28 45-29 45-30 45-3 1 45-32 45-33 45-34 45-35 45-36 45-37 45-38 45-39 45-40 45-41 45-42 45-43 45-44 45-45 4546 45-47 45-48 45-49 45-50 45-51 45-5 2 45-5 3
-.00271 .365 .I31 .239 .270 .248 .284 .0948 .280 .330 .314 .352 .318 .331 .882 .0790 .390 .341 .293 .306 .206 ,216 .237 -2.66 45.1 -4.53 -3.39 -1.15 9.66 4.4 1
11.55
.741 .711 .713 .783 .833 .735 .795 .774 .793 -.141 -.291 .480 .474 -.lo3 .275 -.293 .610 .594 .919 .937 .924 .905 .896 1635. 1673.
a For footnotes, see Table XIII.
.206 .I86 .I01 .138 ,0855 .I46 .175 .I03 .I56 .225 .I75 .347 .132 .0589 -1.15 -.0413 .202 .0896 .I66 .I69 .296 .29 1 .292 4.43 44.6 -11.5 -15.9 -.870 .973 8.862' .985 16.77' .97 1 8.253l .967 87.2Se 50.83k .995 .924 I 7.59f 1334.' .9998 .917 2.634' 38.56l .994 42.96f .978 1374.k .965 18.16k .974 7 1.63f .990 12.14' .927 44.96' .994 1.703' .794 167.9g .997 13.32g .918 3207.' .99992 .999999 192307.f 4.524' .949 5.048' .954 6.131' .962 11.27l .979 24.00f .943 196.7g .997 98.2Ie .990 70.80k .996 .6 12 .859 .07 1 .189 .859 .lo9 .818 .556 .859 .271 .705 .949k .229 .204 .973 .024 .309 .369 .556 .556 .556 .556 .556 .726 .I76 .864 .288 .008 .0142 .00812 ,0328 .0160 .00262 .0207 .00163 .0330 .0184 .0240 .0330 .O 164 .0134 .0474 ,0177 .0278 .0113 .0556 .00117 .000159 .0343 .0321 .0297 1.96 5.29 .305 ,493 .0376
. I 18p .06 16m .0326m .0833m .029Sm .0677" .02 14e .0236e .O1OSk .0269k .0458h .0537g .00346h .00800h .0476" .0514" .018Sk .0473m .0579h .0360: .0731 .195" .0933k .166m .035d .0316g . I 17' .O70Sg .1 5fim .309m .0450" .07770 .021 3g .0448' .0769g .109" .00366g .00339h .000458g .000494g .0989" .107" .loo" .0928m .0927" .0858m 4.18' 1.60" 7.39e 10.4g 1 .4Sk 1 .97m 1.13e .806h .14Sk .0987k
.0142h 4 .00809g 4 .0244' 4 .00699e 15 .O026lg 4 .0132e 9 .00163g 4 .025 2' 4 .0184h 4 .0176g ' 7 .0252g 5 5 .0153g .0090Ie 6 .0453k 7 . I 39" 4 5 .0274g .00961e 5 .0432e 8 .00089ge 4 .000121e 4 .0262h 4 .0246h 4 .0227h 4 1.9Se 4 3.38e 9 .247e 5 .24Ie 7 .0196g 4
MARVIN CHARTON
112
TABLE XLVII Values of pR for Other Unsaturated Systems Set
PR
45-1 45-2 45-3 45-4 45-5 45-6 45-1 45-8 45-9 45-10 a
a
34 39 63 51 51 63 3b9 53
45-11 45-12 45-13 45-14 45-15 45-16 45-11 45-18 45-19 45-20
C
54 53 50 51 51 b
63 65 40
Set
pR
Set
pR
Set
45-21 45-22 45-23 45-24 45-25 45-26 45-21 45-28 45-29 45-30
43 53
45-31 45-32 45-33 45-34 45-35 45-36 45-31 45-38 45-39 45-40
63 t2
45-41 45-42 45-43 45-44 45-45 45-46 45-41 45-48 45-49 45-50
56
63 16
$4
pR
Set
pR
%6
45-51 45-52 45-53
18
a
51
64 t4
50
p was not significant for this set. Correlation was not significant for this set. 01 is a function of O R for this set. a was not significant for this set.
an average PR value of 6 4 for correlations of E,. The correlation of the one-electron reduction potentials (set 45-20) gives a pR value of 40. These results are comparable to those obtained for the 2-substituted 1,4-benzoquinones. The Eo.S values of N4, N, -dimethyl-2-substituted 1,4-benzoquinonediiminium perchlorates gave a value of 53 for PR, significantly less than that observed for the 2-substituted 1,4-benzoquinones. As the set (set 45-22) had only four points, however, no definitive conclusion can be reached. The 3-substituted 1,2-benzoquinones give a PR value of 53. The 4-substituted 1,4-benzoquinones are much more sensitive to resonance effects, with pR values of 63 and 76. The latter value, stemming as it does from a four-point set (set 45-30), is much less reliable than the former (set 45-29), particularly as the former set is very extensive in both number and type of substituents. The PR values obtained for the 5-substituted 3-methoxy-1,2-benzoquinones (set 45-3 1) and the 4,5-disubstituted 1,2-benzoquinones (set 45-32) support the value obtained for set 45-29. The 2-substituted 1,4-naphthoquinones have values of 60 and 74 for pR . The latter value seems high. The 4-substituted 1,4-naphthoquinones show a PR value of 6 6 (set 45-42), in good agreement with the value for 4-substituted 1,2-benzoquinones. The 3,3'-disubstituted diphenoquinone diimines give a PR value of 64. The results obtained for the 2-substituted 1,4-benzoquinones and the 2,5-disubstituted 1,4-benzoquinones show that the composition of the electrical effect is independent of medium. It must be noted that in contrast to the early work cited above, in which correlations were carried out with up, for which pR is 50, best results for most substituted quinone oxidation-reduction potentials show a pR value of about
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
173
60, which corresponds more closely to the UP' substituent constants. There is sufficient variation in pR , however, to require that for best results, correlations should be carried out with either eq. (2) or eq. (30). The magnitude of cr for the 2-substituted 1,&benzoquinones ranges from .166 t o .271, depending on medium for correlations of Eo. The one-electron reduction potentials (set 45-8) show a value of (Y twice as great. The values of (Y observed for the 2,5-disubstituted 1,4-benzoquinones and for the 2,3,5,6-tetrasubstituted 1,4-benzoquinones are comparable to those found for the 2-substituted 1,.l-benzoquinones, in so far as correlation of Eo is concerned. The one electron reduction potentials for the former compounds are also comparable to that for 2-substituted 1,4-benzoquinones. Correlation of Eo for 2,6-disubstituted 1,4-benzoquinones gave a value of cr somewhat less than that observed for the 2-substituted 1,4-benzoquinones. The 3-substituted 1,4-benzoquinones gave a value of cr significantly less than that observed for the 2-substituted 1,4-benzoquinones, as do also the 4-substituted 1,4-benzoquinones. The 2-substituted 1,4-benzoquinones show a wide range of cr for correlation of Eo, from .132 to .347. The 4-substituted-l,2-naphthoquinones show (Y from .090 to .202, depending on whether the Eo values were obtained potentiometrically or polarographically. The 3,3'-disubstituted diphenoquinone diimines show cr values comparable to those of the 2-substituted 1,4-benzoquinones. In addition to the oxidation-reduction potentials data, two sets of infrared carbonyl stretching frequencies were correlated with eqs. (2) and (30). Of these, one set, vCo for 2-substituted 1,4-naphthoquinones, gave significant results, with p R of about 50. While the other set did not give significant correlation, it contained only four points. Although the sharp difference between PR for vco and pR for Eo correlations of 2-substituted 1,4-naphthoquinones is worthy of note, it should not be discussed until it is confirmed by further work. e
C. Multiple Substitution at Nonequivalent Sites Let us consider a system X"X"GY, where X" and X" are substituents at nonequivalent positions m and n of the skeletal group G, which also bears the reaction site Y. Neglecting interaction terms, we may write for the correlation of the quantity Q the expression, ~ m X n = ~ u I , X m t ~ u R , X mXn+&OR,Xnth t~~I,
(104)
In the special case for which Xm- X", we have %mXn = (%I
%&I,
Xm = (Pm +O&R,
Xm
or Qxmxn =01'u,,~m+ $ u R ~ m + h equivalent to eq. (2).
'
(105) (106)
174
MARVIN CHARTON
Two sets of data involving multiple substitution at nonequivalent sites have been examined. The sets studied are reported in Table XLV (sets45-51, 45-52). Results of the correlations are set forth in Table XLVI. Significant correlations were obtained for both sets of data. Sets of the type XmX"GY in which m and n are nonequivalent and in which Xm # X" cannot be handled by correlation with eq. ( 2 ) . Such sets can be correlated with eq. (107):
Q x ~ = xPmurn,xm+Pnon,xn ~ +h
(107) where u, and on are substituent constants defined for or applicable to the m and n positions of the group G . Thus, consider the system 39,
39
in which u, can be used for X3 and up for X4'. Then for 39,
D. Conjugated Dienes and Polyenes Sufficient data are extant in the literature for only one set of substituted dienes. In this set (set 45-53, Table XLVI) is included the value of pKal for muconic acid. This value is reported by Yanovskaya, Strepanova, and Kucherov (247) to be 2.70. Such a value seems impossible, as the pKal for fumaric acid, in which only one double bond intervenes between the carboxyl groups, is 2.98, according to these authors. We therefore calculated pKal for muconic acid from the correlation obtained for the i1pns-3-substituted acrylic acids and the oIand oR constants for the H02CCH=CH substituent. A value of 3.68 was calculated. We have therefore assumed that there is a typographical error in the results of Yanovskaya, Strepanova, and Kucharov, and have used the value of 3.70 for pKal of muconic acid. Correlation of the data with eq. (2) gave significant results. As is predicted from calculations of a and 0,p R is greater than 50, a value of 57 being obtained as compared with a predicted value of 62 to 65. The difference between the predicted and observed values may well result from the fact that there were only four points in the set. It is meaningful, however, that in contrast to most systems XGC02H where G is arylene, vinylene, ethynylene, etc., for which pR is about 50, the value of pR for the trans,trans-divinylene group has a significantly larger pR value. The value of a for the truns, truns-5-substituted 2,4-pentadienoic acids suggests that the conformation in solution is the s-trans (between C3 and C4). Rough estimates give a value of OL of about .8 for the s-trans and of about 1.0 for
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
175
the s-cis conformations. The observed value is -370. As the set included only four points, no definitive conclusion about conformation can be reached. No other data on substituted conjugated dienes are extant in the literature. Of the five nonequivalent positions on a conjugated diene system, no study has been made of the remaining four. Thus the vinylidene (X'), vinylene (X')), vinylidenevinylene (X3), and cis,truns-divinylene positions of 40 remain unexamined. No studies of X2
WY
x5
I X -
x4n
x
3
40
substituent effects on polyene systems extensive enough for correlation with eq.(2) have ever been made. Obviously, this is an area which is worthy of further investigation.
E. Allenes and Cumulenes There are absolutely no data sets for substituted allenes or cumulenes in the literature. This is a situation which should be remedied at the earliest opportunity, as data on these systems would be of considerable theoretical interest.
IX. CONCLUSIONS We shall find it useful to consider three categories of conclusions; transmission of electrical effects, composition of electrical effects, and other conclusions.
A. Transmission of the Electrical Effect In the application of the extended Hammett equation to the system XGY, where X is a substituent and Y is a reaction site, both of which are attached to the skeletal group G, the question of the degree of transmission of substituent effects through G arises. The transmitivity of G is measured by the magnitude of LY and 0. Now,
a = f(G, P, T, Sv, Y, Rg.
. . .)
(1 09) That is, LY is a function of the skeletal group G and its ability to transmit the substituent effect, as well as of pressure, P; temperature, T; solvent, Sv; reaction site, Y; and reagent, Rg. We may write for LYG OG
= 71,Ga
(1 10)
176
MARVIN CHARTON
where T I G represents the transmission character of the group G to the localized electrical effect and w is a term characteristic of all the other variables upon which a! is dependent. Thus, w = f(P, T, Sv, Y, Rg. . . .)
(111)
Now let us consider some reference skeletal group Go. For convenience, we shall choose as the reference skeletal group the p-phenylene group. We define
The quantity YIG is therefore a measure of the transmission of localized electrical substituent effects through the group G relative to the transmission of localized electrical substituent effects through the group G o . Similarly, for the transmission of the delocalized electrical effect, we may write
and
where ~ R Grepresents the transmission capability of the group G to the delocalized electrical effect and w is again a term characteristic of all the other variables upon which P is dependent. Then we define
~ YRG are collected in Table XLVIII. Values of 7 1 and That values of yI and YR vary with the reaction and the reaction conditions is readily seen from the results reported in Table XLVIII for the trans-vinylene group. Values of yI for this group range from 1.01 to 3.28. That the value of y1 is dependent upon the reaction is no surprise. Charton has shown (251, 252) that the yI values may be calculated from the Kirkwood-Westheimer equation in the form
where r and 6 are given in Figure 1. Obviously, r and 0 will depend on the geometry of Y as well as the geometry of G. It is for this reason that p - p relationship of Miller (253-6) shows deviations. It is uncertain why the yIvalues show variation for the same reaction in different solvents. Thus, 71 for the
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 177 Y
Fig. 1. Definition of r and 0 .
ionization of 3-substituted acrylic acids is 2.26 in water, 1.54 in 80% methylcellosolve-water, and 1.01 in 50% ethanol-water. Before any explanation is proposed for this phenomenon, it would be useful to examine a much larger group of compounds in a wider range of solvents. The variation of YR with reaction may be explained by the observation of Charton (257) that yR = m q t c
(117) where q is the charge on the atom bearing the reactiog site calculated by the method of Dewar and Longuet-Higgins in the species YGCH, . As m is a function of Y, it is not surprising that yR will vary with Y. In view of the variation of y1 and YR as a function of Y, the transmission of electrical effects is best compared for a given Y under constant reaction conditions. The most suitable reaction for purposes of comparison is the ionization of carboxylic acids in water at 25". The first observation we may make concerning yI is the fact that all systems in which X and Y occupy vicinal positions and are approximately coplanar (orthophenylene, cis-vinylene, and trans-l,2-cyclohexylene) show similar values of yI of about 2.4. The YR value of the cis-vinylene group is significantly less than that of the orthophenylene group. The value of 71 for groups G with two carbon atoms is, for nonvicinal systems, in the range of about 2, with trans-vinylene having a value of 2.26; ethynylene, a value of 1.86; trans-1 ,2-cyclopropylene, a value of 1.94; and dimethylene, a value of about 1.6 (the results at 18" are for a wider range of substituents and substituent types than those at 25" and are therefore preferable). Introduction of a constant methyl substituent onto the trans-vinylene group causes an increase in yI. Values of YR for the trans-vinylene group and the ethynylene group are about the same: 2.09 and 2.07, respectively. Values of 71 for groups with three atoms between substituent and reaction site range from 1.53 for COCH2CH2 to .907 for CONHCH2. Values of 71 for groups with four atoms intervening between reaction site and substituent include p-phenylene, with yI = 1.OOO, and trans,trans-divinylene, with y1= .970. The YR value for trans,trans-divinylene is significantly less than that predicted from eq. (1 17), however. The discrepancy may result from the fact that the set from which Y R
c 4 00
cisCPh=CHcisCMe=CH-
PhCN,
50% EtOH-H,O EtOH 50%EtOH-H,O HZ0
H2O
trans-CMe=CHtrans-CH=CMecis-CH=CH-
H, 0 80%Methylcellosolve-H ,O 50%EtOH-H,O OHH,O 70% (v/v) dioxane-H20 MeOH MeOH Ph2CN, EtOH
Ph,CN,
80% Methylcellosolve-H,O
H2O
Reagent Solvent
50%EtOH-H,O
CO,H
C0,Et
CO,H
CO,H
Y
transCPh=CH-
iransCH=CH
G
Values of 7 and pR
TABLE XLVIII
25 25 25 30 25 25 25 25 18.8 35 30 30 25 25 25 25 25 25 30 25 25
T
15
2.25 2.55
d
55 51
3.43 2.65 1.56 3.25
49 45
d
39 71
42 50 59 d
d
63 52
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
10
10 10
a b
50a
25b 49 44 40 48 56
Ref. pR
1.23 1.70 3.44 d
d
1.OOoa .333b 2.31 1.13 1.11 2.09 1.99 3.01 3.05 1.87
1.OOoa
l.OOOb 2.40 1.45 1.62 2.26 1.54 1.01 1.79 1.75 3.28 1.73 1.72 2.42 2.08 2.84 2.58 2.41 1.30 2.02 2.35 3.14
TR
TI
W
4
c1
a
’’
,
80% Methylcellosolve-H,O HzO
H2O
50% EtOH-H,O
H2O
50% EtOH-H,O
25 25 25 25 25 25 25 25 18 25 25
25
25 25 25 25 25 25 25 25 25
4.14 3.39 2.12 4.25 2.68 2.70 ,870 1.94 1.90 6.38 1.86 7.69 .56 1.18 3.78 1.53 .907 1.31 1.61 2.32 3.95
.873
d
.656
.828 .923 5.41 2.07 3.99 .38f 1.47 1.57
1.15
2.92
d d
d d
By definition. Calculated from c for urn. This work. B was not significant for this set. This set is of the type XY,that is substituent and reaction site are directly joined to each other. Calculated from for 0;.
trans-2-cyclo-C, H,, CH,
trans-CH=CHCH, WCCH, WCCH,CH, O=CNHCH, CH,CH,
f16H4CH2
trans, tmns-CH=CH-CH=CHtrans-cyc1o-C,H, trans-cycloC,H,Me, cycld: ,Ha CZ nonee
cis-CPhH=C
CH,=Ccis€PhH=C-
42 0 0 0 0
d
29
55
57 30 33 46 53 34 40
d d
41
d
17
d
c
29 29 19 29
c
9
c c
c
180
MARVIN CHARTON
was calculated contains only four members and therefore the value of 0 is uncertain. The value of YR calculated from eq. (1 17) for the XC02H in which there is no group G is in very good agreement with the observed value. The vinylidene group, the trans-CPh= C- group, and the methylene group, all of which have one atom intervening between the substituent and the reaction site, all show y~values of about 4. The cyclopropylidene group is an exception to this observation, with yI of 6.38. As there were only four points in the set from which a was obtained, this deviation may not be real. The C-CPh=C group has a somewhat low value for yI of 3.39. The introduction of a methylene group between G and Y results in a decrease in y1by a factor of about .5,as is shown by the yIratios of p-C6H4CH2 to p-C6H4, trans-CH=CHCH, to trans-CH=CH, and COCH2 CH2 to COCH2 . Values of y1 for the COCHz and COCH2CHz groups are larger than would be expected from the number of atoms intervening between substituent and reaction site. It is of interest to compare the ratios ac/aT and &//3T for the vinylene group. Values are reported in Table XLIX. Of the 1 1 sets for which the comparison can be made, 10 sets have aC/aT> 1. If the localized effect were an inductive effect, the values of ac would of course be equal to those of aT, and therefore the ratio aC/aT would show values scattered about 1.000, with an equal probability of being greater or less than 1.000, The observation that in general the values are greater than 1.OOO excludes the inductive effect as the sole factor in the localized effect and strongly suggests that the localized effect is a field effect. From eq. (1 17), we would predict that 0c should equal 0~ and should be scattered about 1.000 with an equal therefore the ratio probability of being more or less than one. This result is in fact observed, with five values greater than and six values less than 1.OOO. TABLE XLIX Values of 'YC/'YT and pc/PT cis Set
trans Set Q
Y
Solvent
"C/"T
PC/PT
12-5 12-6 12-1 1 12-12 12-15 12-16 12-17 12-18 12-20 12-21 12-19
8-1 8-3 8-8 8-5 8-15 8-16 8-17 8-20 8-22 8-23 8-21
CO, H
H,O 50% EtOH-H,O
1.07 1.28 1.13 1.15 1.17 1.10 1.08 1.77 ,757 1.52 1.37
.746 1.08 .85 1 .744 1.48 1.29 1.21 SO4 .851 .goo 1.05
PKa
7 ,
H2 0
kr " "
v
6 v
z
C0,Me H H H
EtOH t-BuOH EtOAc CCI,
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
181
B. Composition of the Electrical Effect From the previous discussion, in which it was pointed out that both a and 0 must be functions of Y, we see that PR, which is a function of a and 0, must also be a function of Y. It will therefore be convenient to compare the composition of the electrical effect transmitted by various groups G with Y and the reaction conditions held constant. Again, the most useful reaction for this purpose is the ionization of carboxylic acids in water at 25". Not only are there more sets of data available for this reaction than for any other, but the sets studied for this reaction generally include more substituents than d o sets for other reactions or under other reaction conditions. The value of PR observed for the trans-vinylene group is 48. Substitution of a methyl group on the trans-vinylene group gives comparable values of 51 and 55. The ethynylene group gives a comparable value of pR of 53, as does the ortho-phenylene group, which shows a value of 49. By contrast, the cisvinylene group shows a pR value of 39. The cis-vinylene group bearing a constant trans-methyl substituent gives a value of pR of 45, in much better agreement with the ortho-phenylene value. The cyclopropylidene group also gives a comparable value, with pR of 46. This system requires further investigation, however. The p-C6H4CHZ group shows a pR yalue of 40. Surprisingly, the trans-CH=CHCHz group shows a value of 55. This result is unexpected, as the methylene group prevents direct resonance interaction between the carboxyl group and the substituent and vinylene group. It would be useful to verify this observation by a more detailed study of this system. Of particular interest is the value of pR of 42 observed for the CONHCH? group. This value is significantly larger than the pR value of 29 observed for the COCH? group. If this result is verified, then it would seem that the CONHCH? group has a significant contribution of the structure HO-C=N-CHz -: that is, there is considerable double-bond character in the C-N bond. The vinylidene group shows a pR value of 17. Surprisingly, the trans-styrylidene group has a value of pR of 41. Again, it would be useful to verify this result. The trans-cyclopropylene group shows a value of pR of 30, thus clearly establishing the ability of the cyclopropylene group to transmit resonance effects t o some extent. The trans,trans-divinylene group has a pR value of 57, somewhat greater than the pR values observed for p-phenylene, trans-vinylene, and ethynylene. C. Other Conclusions Of the 389 sets studied, 294 gave significant correlations. In the majority of the sets which did not give significant correlation, only four or five points were
182
MARVIN CHARTON
extant. There is no doubt that had more data been available, significant correlation would have resulted in at least 90% of the sets studied. We conclude, therefore, that linear free energy relationships in general and the extended Hammett equation in particular are applicable to data for nonaromatic unsaturated systems. Our results show the importance of resonance effects in all the systems studied. Furthermore, there is considerable variation of PR with structure. It is therefore difficult in most cases to recommend correlation with the Hammett equation with use of simple substituent constants such as urn, ,:u up, or ui. We therefbre recommend that data for nonaromatic unsaturated systems be correlated with the extended Hammett equation for best results. References 1 . Hammett, L. P., Physical Organic Chemistry, McGraw-Hill, New York, 1940. 2. Jaff6, H. H., Chem. Rev., 53, 191 (1953). 3. Taft, R. W., in Steric Effects in Organic Chemistry, M. S . Newman, Ed., Wiley. New York, 1956, p. 565. 4. Stock, L. M., and H. C. Brown, Adv. Phys. Org. Chem., I , 35 (1963). 5. Leffler, J. E., and E. Grunwald, Rates and Equilibria of Organic Reactions, Wiley, New York, 1963. 6. Palm,V.,Russ. Chem. Rev., 31, 471 (1961). 7. Wells, P. R., Chem. Rev., 6.3, 17-4 (1963). 8. Ritchie, C. D., and W. F. Sager, Jr., h o g . Phys. Org. Chem., 2, 323 (1963). 9. Wells, P. R., Linear Free Energy Relationships, Academic Press, New York, 1968. 10. Charton, M.,Prog. Phys. Org. Chem., 8, 235 (1971). 1 1 . Wells, P. R., S. Ehrenson, and R. W. Taft, Prog. Phys. Org. Chem., 6, 147 (1968). 12. Jaffk, H. H., and H. L. James, Adu. Heterocyclic Chem., 3, 209 (1964). 13. Evans, E., and J. DeHeer, Trans. Faraday Soc., 47, 801 (1951). 14. Harnsberger, H. F., E. L. Cochran, and H. H. Szmant, J. Am. Chem. SOC., 77, 5048 (1955). 15. Charton, M., and H. Meislich, J. Am. Chem. SOC.,80, 5940 (1958). 16. Hine, J., and W. C. Bailey,J. Am. Chem. SOC.,81, 2075 (1959). 17. Hine, J., and W. C. Bailey,J. Org. Chem., 26, 2098 (1961). 18. Charton, M., J. Org. Chem., 26, 735 (1961). 19. Charton, M., 1.Chem. Soc., 1964, 1205. 20. Taft, R. W., and 1. C. Lewis,J. Am. Chem. SOC.,80, 2436 (1958). 21. Taft, R. W.,J. Phys. Chem., 64, 1805 (1960). 22. Swain, C. G., and E. C. Lupton, Jr., J. Am. Chem. SOC.,90, 4318 (1968). 23. McDaniel, D. H., and H. C. Brown,J. Org. Chem., 23,420 (1958). 24. English, P. J. Q., A. R. Katritzky, T. T. Tidwell, and R. D. Topsom, J. Am. Chem. SOC.,90, 1767 (1968). 25. Sheppard, W. A., private communication to Ref. (24). 26. Taft, R. W., private communication to Ref. (24). 27. Oue, S., and C. C. Price, J. Am. Chem. SOC.,80, 3425 (1958). 28. Fraenkel, G., and J. P. Kim,J. Am. Chem. Soc., 88,4203 (1966). 29. Charton, M., J. Org. Chem., 29, 1222 (1964). 30a. Brownlee, K. A., Statistical Theory and Methodology in Science and Engineering, 2nd ed., Wiley, New York, 1965.
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS
183
30b. Crow, E. L., F. A. Davis, and M. W. Maxfield, Statistics Manual, Dover, New York,
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185
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r W
X
'ZH3
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-CH,CH, Me Me
\ -Me
Q
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Ref.
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0.00
f.
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.36 .42
.64 .35
01
X
-.22 .05 .13 -.06 -.23 .03 .14 -.I 1
f
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CH,CO,Et CONH, PO(OEt), PO(OCH,CH,Cl), EtSO, EtCO HO,CC,H, HOCH,C,H,
-.15
i-PrCH,CH, PhCH, Bz trans-MeC, H, 2-fury1 Me,N CH,OMe CH,OBz CH,NMe:BrCH,F 3-O,NC6H, CH,CHIOH MeCHOHCH,
cc1,
CH,OAc CICH,CH, O
p
Ref.
.14 a -.09 -.06 -.03 -.06 -.11 .07 -.12 -.03 .08 -.35 .19 -.12 m -.14
OR
aa
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'
Ref.
.29 .21 .09
.52 .52
' '
hh
;;
.14 bb .05 cc
.15 .25 .18 .19 0.00
.10
.29
.43 -.03
01
Substitutent Constants from Sources other than Ref. (23) and Ref. (29)
APPENDIX 1
hh
gg
;;
' 'dd
bb
' '' ''
"
'
Ref.
.09 mm -.05 mm -.11
-.08 .09 .08 .08 .13
-.05 -.lo
-.08 -.05 0.00 -.04 -.01 -.lo -.13
-.13 0.00
.02 -.12 -.14
OR
c
W 0
.20
-.07 .08
.27
-.01
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' '
zk
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Ref.
.34 jj -.04
01
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'
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-.09 -.12 -.40 -.34 -.12 -.21 -.15 k .17 kk -.07 -.53 'I -.05
-.05
-.01
.I1 jj -.11
O R Ref.
cycloC6Hl Oi-Pr cycloC,H, Me,C=CH NHPh ' MeO,CCH,CH, 4C,H,NO, 442, H,MeO C,H,CH, r-BUS C,H,O r-BuCH, cycloC,H,CH, BzO
X
.23 .35 -.02 -.02 .45
.22 .09
.05
.15
.26 -.02
01
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Ref.
-.21 -SO -.15 -.12 -.23
-.08
'k k ' 'k
'
nn
Ref.
-.19 b 00 -.12 k -.55 -.09 .01 -.I8
-.12
UR
Calculated from the up value obtained from the equation up, XCH, = 0.522 UI,X -0.131. Ref. (37). M. Charton, J. Org. Chem., 34, 1882 (1969). Ref. (8). Calculated as in a from up values reported by Ref. (2). From M. Charton, Abstr., 154th Meeting of the American Chemical Society, Chicago, 1967, S 137. M. Charton and B. I. Charton, J. Chem. Soc. B, 43, (1967). Calculated from the up value estimated by the method of M. Charton, J. Org. Chem., 28, 3121
Calculated from om and up values reported by J. K. Kochi and G. S. Hammond, J. Am. Chern. Soc., 75, 3452 (1953).
(1963).
j
i
I
Calculated from the pKa of 4-nitro-[2,2,2] bicyclooctane-1-carboxylicacid using p = 1.65. The value of UR was calculated from UR = up - UI by use of the value of up given by Ref. (23). Ref. (215). Calculated as in a from up values reported by 0. Exner and I. Jon&, Coll. Czech. Chem. Cornrnun., 27, 2296 (1962).
a
Ph,Si EtOCH, PhO MeO,CC,H,
'ZH3'
Bu0,C nCsH13 NCCH, CCI, CH, EtO,CCH,CH, MeO,CCH, 04C,H,NMe, AcNHCH, Me,SiCH,
X
c. W c.
JJ
'
"
Assumed equal to 01 and O H for C,Il,CH,CII,. Assumed equal to 01 and O K for C,II,CH,CH,CH,. Calculated from up reported by H. H. Szmant and G. Su1d.J. A m . Ckern. Soc., 78, 3400 (1956). Calculated from up reported by C. Y . Meyers, B . Cremonini. and L. Maioli, J. A m . Ckem. Soc., 86. 2944 (1964). Estimated as described by M . Charton, Abstracts, 148th Meeting o f the American Chemical Society, 1964, p. 56-V. M . Charton, J. Org. Ckem., 34, 1877 (1969). up estimated from a plot of ul vs. up for CIInC13-n, U R calculated as in ". Ref. (37), calculated as in '. ( I S ) , calculated as in '. " Ref. Ref. (60), calculated as in '. W Ref. (170), calculated as in '. Calculated as in ',assuming U ~ , C H , O M=~U ~ , C H , O H , Calculated from pKa for C,H,CH,CO,H. Calculated as in a from up values reported by E. Berliner and L. €I. Liu, J . A m . Ckern. Soc., 75, 2417 ( i i 5 3 ) . Calculated from pKa of HOCH,CH,CH,CO,H. bb M. Charlon,J. Org. Ckem., 30, 3346 (1965). cc Calculated from pKa for ClCH,CH,CH,CO,H. dd From up value reported in ref'. of k, calculated as in a. ee Calculated from urn and up values reported by L. D. Freedman and H. H. Jaffk, J. A m . Ckem. Soc., 77,929pY55). Assumed equal t o substituent constants for PO(OEt), . gg Assumed equal t o O R for MeSO,. h h M . Charton,J. Org. Ckem., 36, 266 (1971). k Calculated from um and up values estimated as in . Assumed equal t o substituent constants for C0,Et. kk Calculated from um and up values reported by R. A. Benkeser, C. E. DeBoer, R . E. Robinson, and D. M. Sauve, J. A m . Chem. SOC., 78, 6 8 2 (1956). I' Calculated as in a from up values reported by M . Charton, J. Ckem. SOC., 5884 (1964). mm , up, x-0.0179. Calculated asin a from up valuesestimated from the equation up, t r a n s - x c , =~ 0.388 nn Calculated as in ', assuming up, cyclohexyl = up, j.pr, 00 Assumed equal to U R for trans-MeC,H,.
rn
192
MARVIN CHAKTON
APPENDIX 2: DATA USED IN CORRELATIONS Abbrevia1:ions used in this appendix are as follows: Vi 1-Vn
vinyl vinylidene (e.g., 1-MeVnCI is CH,= CClhAe)
2-Vn
vinylene e.g., trans-2-MeVnCl is
2-Pn 3-Pn 4-Pn
ortho-phenylene meta-phenylene para-phenylene
Set
Ref.
Data
2-1
Table 2
H , O ; F , 1.427;C1, 1.44;Br, 1.117;1, 1.27;Me, -.364;Ph, .13;C,H, .43;CF,, 2.45;CN, 3.89;NOZ,3.44;Me3Si, 0 H , . 1 3 ; P , 1.36;C1, 1.41;Br, 1.56;Me, -.72;Ph,0;CN,4.17;N02,4.54 H, .364;F, 1.85;C1, 1.97;Br, 1.69;Me,O;Ph, .72;C,H, .94;CN,4.53 H, -1.417;CI,O;Br,O;I, .39;Me, -1.69;Ph, -1.4 H, -1.452;CI,O;Br,O;Me, -1.97;Ph. -1.41;Me3Si, -1.71 H, -3.89;Me, -4.53;Ph, -4:17;CN,O H, .364;F, 1.60;C1, 1.69;Br, 1.51;Me, -.503;Ph, .76;CN, 3.69 H, .13;C1, 1.93;Me, -.76;Ph, .5 H , O ; F , 1.417;C1, 1.43;Br, 1.41;Me, -.38 CN, 10.91; CH,OH, 9.67;CH2C1, 10.04;CHZBr,9.7;CF3, 10.90; C,H3,9.07;C,H, 9.87;Me, 9.73;Et,9.58;Bu,9.46;BuCH2,9.54; F , 10.37;Cl, 10.00;Br, 9.80;13, 10.51;CHO, 10.10;Ac.9.91;CO,H, 10.90; OMe, 9.93; OAc, 9.19 Me, 9.13;Et, 9.06;Pr, 9.16; Br, 9.30; H, 9.73;CHO, 9.73 F , 2.55;Ph, 3.84;H, 4.26;Me, 4.65;Bu. 4.80;As03H-, 4.225; SeCN, 1.896; PO,H-, 3.5 Br, 1.84;C1, 1.97;1, 2.24;Ph, 3.74;H, 3.88;Me, 3.62 H, 5.38; Me, 5.10; Br, 3.55; C1, 3.73 H,5.18;Me,4.95;Cl, 3.40;B1,3.38;1,3.56
(
2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10
2-1 1 5-1 5 -2 5-3 54 5 -5 5 -6 5-7 5-8 5 -9 5-10 5-1 1 5-12
5-13 5-14
Table 5
Me.-'
--/")
Br,3.03;C1,3.02;1,3.30;F,:i.71;Ph,4.71;H,4.44;Me,4.82 H. 5.77;Me,6.10;Br,4.28;CI., 4.30 H, 5.55; Me, 6.00; C1, 4.10; BI, 4.15; I , 4.34 CI, 3.22; H, 4.70; Me, 4.96; A;iO,H-, 4.61 CN, 3.04;CO2Et, 3.36;CONH2,3.95;H, 5.12;Me,4.42 Br, ,190; CI, ,158; H, .218; Me:, 3.44 Me, 14.88; Ph, 6.46; CO,Et, 2.38; H, .46 H, O;alkyl, .44;cycloalkyl, .71;CH,O, .67;CH,I, .67;CH,S, .53; CH,CI, .72;CH,Br, .72;CN, .23;CO, l.lO;CO,H, 1.00; CO,R, .84; CHO, 1.03; NCO, 1.37; COCI,l.lO; OR(aliphatic), 1.18; OR(conjugated), 1.14;OCOR, 2.09; aromatic, 1.35; C1, 1.00; Br, 1.04; NR,(aliphatic), .69; SR, 1.00; SO,, 1.58 F, -.84; OMe, -1.10; C1, -.9'7; Br, -1.16; Ph, -1.36;CN, -.20; i-Pr, -.34; H, 0 F, 388.72; C1, 371.08; Br, 381.35; I, 389.09; OMe, 386.0; SMe, 380.7; CN, 328.10; CHO, 375.62; H, 318.5
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 193 Set 5-15
Ref.
5-16 5-17 5-18
Data Me. -.40;H,O;Ph,-1,36;Br, -1.16;CI, -.97;CO2Me,-.66;Ac,-.95; CN. -.20;NO,, -1.79 H. -.19;CO,Me, -.83;Me, -.51;Ph,-1,2l;Cl, -.99 H. -.55;CO,Me, -1.15;Me. -.75;Ph, -1.55;Br, -1.29 H, -.38;CO,Me, -.98;Ac, -1.32; Me, -.91;Cl, -.87;Br, -1.37; Ph, 1.66; CN, .44; CHO, -1.32; COCI, -1.26 ;NO,, -2.18 H. .37;CO,Me. -.43;Me, .08;CI, -.55;Br, -.62;Ph, -.91;CN, .02; CHO, --.70;COCI, -.76;NO,, -1.62; Ac, P.68 CN. -206.0;CI, -234.3; Br, -248.0; Me, -216.3 H, -.89;Me, ---1.54;CI,-1.98;Br, -2.24;COZMe, -1.41;Ac, -1.61; COCI, -1.63; Ph, -2.23 H. -.76;CO,Me. -1.24;Me, -1.43;Ph, -2.12 H,4.255;Cl, 3.79;Br,3.71;1, 3.74;OMe,4.85;N0,,2.58;CH2C1, 4.140;CI;,, 3 . 1 5 ; C 0 2 H . 3.396; CO,Et, 3.396;Ac, 3.238;CO;, 4.301; Me. 4.693; Et,4.695; PI, 4.703; i-Pr, 4.701; trans-2-PhVn, 4.427 -
5-19 5-20 5-2 1 5-22 8-1
rable 8
-
Me
8-2
8-3
8-4 8-5 8-6 8-7 8-8 8-9 8-10 8-1 1 8-12 8-13 8-14 8-15 8-16 8-17 8-18 8-19 8-20 8-21
8-22
0
--CH,CH;, 7.05; Me, C=CHCII,CH, -C=CIICH,CH, ; 7.12; I Me Me Me CO,H, 5.40;CO;. 6.52 H,5.50;PhS,5.78;PhSO,4.30;PhSOz,3.79;Ph,5.77;Me,5.53;~, CH,CI, 4.88 Me, 4.96; H, 4.65; Ph, 4.82; CI, 4.03; MeO,C, 3.452; EtO,C, 3.468 C1,4.07;Br, 3.98;1, 3.90;H,4.44;Me,5.12;Et,5.15;C02Et, 3.26 Ph. 4.5; H, 3.880;C1, 3.57; Br, 3.592; I, 3.636 H, 5.38;Me,6.13;Br, 4.85;C1,4.98 H . 5 . 1 8 ; M e , 6 . 0 0 ; C I , 4 . 7 7 ; B r , 4.72;1,4.79 H, 4.37; CI, 4.12; Me, 4.507; Et, 4.516; CH,CO,H, 4.28; CH,CO;, 4.70 H. 10.95;Ph, 10.23;CONH2,9.67;C0,Me,9.40;CN, 7.81; 4-Me2 NC, H, , 10.29 H. .779; Me, .130;CO;. .158;CO,Et, 2.235 H.41.1;Me.4.20;C1,149.;Br,209.;i, I,159;OMe,2.24 H, 20.0;Me. 9.07;CI, 5.13;Br, 5.99;I,4.10;OMe,4.70;N02, 2.62 Me, .61;H, 1.27;C1, 2.48;Ac,4.03;HOZC, 3.36a;C1,CH, 2.36; CI,C, 5.39; O,N, 21.8 H, 1.32;Me, .587;C1, 2.68;Br, 3.31;1, 3.20;OMe, .450;NO,, 21.5 H . ,447; Me. ,181; CI, 1.1 1; Br, 1.49; I , 1.44 H. .230;Me, .0573;CI, .933;Br, 1.13; I, 1.06 H. 1.00; CI, .6; Me, 17; Ph, 5 0 H . 1.00;C1, 1.01; Me, 95; Ph, 8800 H, 1735;Me, 1730;Cl. 1733;Br, 1733;I, 1733;OMe, 1713 H. 0: alkyl, -.29; cycloalkyl, -.30; CH,O, -.07; CH,I, -.07; CH,S, -.15; CH,CI, .07; CH,Br, .07; CN, .58; CO, 3 1 ; CO,H, .74;CO,R, .56; CHO. 1.21; NCO. .35;COCI, .99;OR(aliphatic), -1.28; OR(conjugatedj, -1.28; OCOR, -.67; aromatic, -.lo; C1, .03; Br, .55; NR,(aliphaticj, --1.31;SR, -.04;SO,, .95 F, 1.30;OMe, 1.43;CI, -.11;Br,-.70;Ph,.12;CN, -.72;i-Pr,-.56; 3. H, 0
MARVIN CHAA.TON
194 Set 8-23
Ref.
12-1
Table 12 H,3.76;C1,2.13;Br,2.23;I,2.31;Me,4.19;Et,4.0;i-PrCH,CH,,4.16; CO,Et, 1.8;Ac, 1.8;NO,, 1.68;PhCHZ,3.69 O H , 5 . 1 a ; H , 2 . 7 1 ; F , 1.40;C1,.73;Br, .80;NO,, -3.0 OH, 6 . 5 b ; H , 5 . 1 8 ; F , 3.30;Cl. 3.08;Br, 3 . 1 0 ; N 0 2 , -.5 H, 4.00;CH2CH,-i-Pr, 5.13; Bz; 2.17; trans-2-MeVn, 4.8;Ph, 4.35; PhCH,, 4.9 Me,4.42;H,4.25;Cl, 3.45;C02Et, 3.08;COZH,2.21;2-furyl,4.11; Ph, 3.88;Br, 3.32; I, 3.42 H, 5.5; PhS, 5.93; PhSO, 4.10; I’hSO,, 3.69; Ph, 5.38 H. 4.65; Me, 4.30; PI, 4.44; Ph, 3.62; CI, 3.05 Me, 4.07; Ph, 3.57; H, 3.32; CO,Me, 2.8 H,4.44;Ph,4.5;Cl, 3.56;1, 3.39;PhCHZ,4.11 H,5.77;Me,6.16;Br,4.78;CI, 4.94 H, 5.55; Me, 5.99; C1, 4.79; Br, 4.64; I, 4.49 Me,5.12;Et,5.13;H,4.693;CI, 3.91;Br, 3.74;1,3.77 H, 20.0; Me, 3.87; C1, 3.40; Br, 3.82; I, 1.62
12-2 12-3 12-4 12-5 12-6 12-7 12-8 12-9 12-10 12-11 12-12 12-13 12-14 12-15 12-16 12-17 12-18 12-19
12-20 12-2 1 12-22 12-23 12-24 12-25 12-26 12-27 12-28 12-29 12-30 15-1 15-2
”
Data F , 258.71; CI, 316.22; Br, 350. 21; I, 387.39; OMe, 232.7; SMe, 304.5; CN, 346.2;CHO, 376.87;H, 318.5
H,41.l;Me,2.36;C1,36.5;Br,23.1;1,15.0 H, 1.32; Me, ,437; C1, 2.32; Br, 3.09; I, 2.68 H, .447;Me, ,125; C1, .920;Br, 1.31; I , 1.14 H, .230;Me, .0401;C1, .646;Br, .976; I, .909 H, 1735;Me, 1728;C1,1742.5;Br, 1740.5;1, 1739.5 H, 0; alkyl, -.26; cycloalkyl, -.33; C H 2 0 , -.02; CH,I, -.02; CH,S, -.15; CH,Cl, .12; CH,Br, .12; CN, .78;CO, 1 . 1 3 ; C 0 2 H , 1.35; CO,R, 1.15;CHO, .97;NCO, .93;COCl, 1.41;OR(aliphatic), -1.06; OR(conjugated), --.65; OCOR, -.40; aromatic, .37; C1, .19; Br, .40; NR,(aliphatic), -1.19;SR, -.24;SO,, 1.15 F , .96;OMe, 1.29;CI, -.19;Br, -.55;Ph. -.38;CN. -.58;i-Pr, .48; H, 0 F,281.65;Cl, 324.20;Br, 345.10;1, 371.36;OMe, 241.8;SMe, 290.4; CN, 358.0; CHO, 367.62; H, 31 8.5 Me, .37;H,O;Ph, -.38;Br, -.585;CI, -.19;CO,Me, -.89;Ac, -.76; CN, -.58;NO,, -1.22 H, -1.16;C02Me, -2.24;Me, -.62;Ph, --1.37;Br, -1.29 H, -.97;CO,Me, -1.98;Me,-.55;Ph, -.87;C1, -.99 H, -1.36;CO2Me, -2.23;Ac, --2.12; Me, -.91;C1, -1.21;Br, -1.55; Ph, -1.66;CN, -1.99;CHO, -2.lO;COCl, -2.47;NOZ, -2.59 H, -.40;CO,Me, -1.54;Ac, -1.43;Me, .08;C1, -.51;Br, -.75;Ph, -.91;CN, -1.35;CHO, -1.46: COC1, -1.86;NOZ, -1.89 CN, -256.5;C1, -234.8; Br, -241.5;Me, -216.3 H, -.66;Me, -.43;C1, -.83;Br, -1.15;COZMe, -1.41;Ac, -1.24; COCI, -1.63; Ph, -.98 H, -.95;CO,Me, -1.61;Me, -.68;Ph, -1.32 H, -416.74;AcO. - 4 0 4 . 9 5 ; 0 1 ~ ,-368.97;OMe, -372.60; MeS, -396.46; Me, -408.68; Ph, -423.53; C1, -435.39; Br, -453.04 Table 15 CO,H, .09;CHO, .19;CH,OH, 5.17;Et,62.2;Me,29.2 ” Me, .57;H, .71;C1, 1.20;NOZ,5.51;CN,4.11;Ac, 1.21;MeO, .18; F, .85; Br, 2.11; I, 1.95; CO,M:, .72
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 195 Set 15-3 15-4 15-5 15-6
15-7 15-8 15-9 15-10 15-11 15-12 15-13 15-14 15-15 15-16 15-17 15-18 15-19 15-20 15-21 15-22 15-23 15-24 15-25 15-26 15-27 15-28 15-29 15-30
Ref.
Data H, .71; Me, .41;C1, 10.27;Br, 6.66; I, 3.62 NO,, 2.32; CN, 2.55;Ac, 2.73; MeO,C, 2.78; F, 2.86;Cl, 2.80; Br, 2.79; I, 2.82; Ph, 2.90; H, 2.98; Me, 3.02; MeO, 3.12; Me,N, 3.35 CHCl,, .60; Br, .28; SO,H, .11; CO,Et, .056; CO,H, .18; CCl,, .006; SO,Me, .0001;CN, .0001 Me, 2.0; H, l.O;CH,F, 3.4 x lO-’;CH,Cl, 1.9 x lO-,;CH,Br, , X ~ O - ~ ; 1.3 x lO-’;CH,CN, 2.7 x 10-3;CHCl,, 2.6 x 1 0 - 5 ; B ~1.3 CCI,, 2.9 x lo-’ Bz, 61;Br, 30; 3-O,NC6H,, 15;CO,Me, lO;CO,H, 4.9;CHO, 1.8; CN, .022; NO,, .020 CO,Et, 1.06 x lo-’, CH,CN, 440; H, 3.9 x 10’; Me, 4.5 x lo6; CH,NMe:Br-, 2.84 x lo-’ CO,Et, 6.7 x 10-’;CH,NMe+J3r-, 9.1 x lo-’; CH,CN, 100; H, 2 x lo4; CH,OH, 6.9 x l o 4 ;Me, 3.2 x l o 5 CO,Et, CO,Et, 3.4 x lO-’;CO,Et,Me, 2.76;C1,CHZOH,3.08; Ph,CH,NMelBr-, 37; CO,Et,F%, 220 CO,Et,CO,Et, 3.7 x 10-‘;CO2Et,Me, 1.04;CI,CH20H, .31;Ph, CH,NMeiBr-, 4.8; CO,Et,Ph, 2.3 Ph, 11,00O;Bu, 2,000; H, 84;CH,OAc, 10;CH,OBz, 14;CH,CI, 1.6; CH,Br, l.O;CH,CN, .23; Br, .0011; CO,Et, .004 CH,Cl,77;Ph, 18;Br,O.ll;CO,H,O.l9;H, 11,000 H, 1.481, Et, 3.462; F’I, 3.320; Bu, 3.299; S-Bu, 2.966; CH,-I-Bu, 2.539; OEt, 8.54; OAc, 3.36 CH,OBz, 9;CH,Cl, 3.8;CH2Br,2.2;Br, .012;CO,H, .44 CH,Cl, 16; Ph, 8; Br, .07;CN, 4.0; NO,, 1.0 H, l;CH,Cl, l;CH,OMe, 30;Ph, 5000; Me, 8000;Et, 10,000; I-Bu, 8000 H,4.81;F, 340;C1, 1.70;Br, .395 H, 5100; Me, 100,000; Et, 80,000; CH,OH, 1120; CH,CH,OH, 8400; MeCHOH,CH,, 6100; CH,Cl, 11; CH,CN, 4.3 Et, 1.195; Ph, .6021; PhCH,, .9542;CICH,, .1761; Me,Si, ,3076; F3C, -.4543; ClCH,CH,, .6585; EtO,CCH,, .6886 CONH,, 2.00; CO’Me, 46.0; CN, 13.7; SO,Me, 90.0 CONH,, 6.30; PO(OCH,CH,Cl),, 20.9;CO2Me, 182;CN, 50.0; SO,Me, 306; Ac, 4000 CONH,, 16.9; CO,Me, 528; CN, 203; SO,Me, 1120 CONH,, 3.50; PO(OCH,CH,Cl),, 10.7;CO2Me, 111;CN, 35.3; Ac, 2280 Ac, 26.4; EtSO,, 2.46; CN, .732;CO,Me, .21; EtCO, 14.1 PO(OEt),, 1.43;CONH2,3.57;CN, 56.8;C02Me, 104;Ts, 755; CO,Ph, 1410; Ac, 12,000; CHO, 12,800; Bz, 40,500 PO(OEt),, .233; CONH,, S61; CN, 14.4; CO,Me, 32.8; Ts, 187; Ac, 3770; CHO, 6490; Bz, 20,800 PO(OEt),, 33.1;CONH2, 65.1;CN, 106;CO,Me, 162;Ts, 1200; CO,Ph, 2270; Ac, 23,300; CHO, 17,000; Bz, 49,200 Ac, 1900;CO,Me, 1030; CN, 1730; Me, 21.9; Ph, 790; H, 34; OEt, 8 ; Vi, 104Sa; OAc, 37 CO,Me, 1440; CN, 2120; H, 21.9; Me, 35.6; Ph, 86
MARVIN CHARTON
196 Set 15-31 15-32 15-33 15-34 15-35 15-36 15-37 15-38 15-39 15-40 15-41 15-42 15-43 15-44 15-45 15-46 1 547 15-48 15-49 15-50 15-51 15-52 15-53 15-54 15-55 15-56 15-57 15-58 15-59 15-60 15-61 15-62 15-63 15-64 15-65
Ref.
Data H, .57; Bu, .56; CH,OAc, .68; OEt, .77; OAc, .80; Ph, 2.26; BuO,C, 2.54; CO,Me, 2.54; CN, 2.93 C,H,,, 1.03;Ph, 2.56;OAc, 1.28;OBu, 1.2O;CN, 3.17 F,7.1;C1,36.7;H, 74.8;Me,92.6;Ph,404;Vi, 371a F,4.9;CI, 18.6;H, 29.2;Me,32.7;Vi,94a Me,H, 108.6; Me,Me, 342.5; F,H, 15.5; F,Me, 51.8; CI,H, 66.8; Vi,H, 434a Me,H,93.0;Me,Me,278;F,H,7.0;F,Me, 31.7;Cl,H, 36.8;Vi,H, 391a Ph, lOO;Vi, 9a;BuCH,CH,, l.O;OAc, .8; PhCH,, .7;CICH,, 0.5; .:H NCCH,, .3;CCI,CH,, .3 H , 23.4;Me, 10.4;Et,9.6;Pr, 7.1;Bu,6.6;C1,40.6 H,H, 23.4;Me,Me,5.7;Me,BuCH,,4.2;CO2Et,CO2Et, 6.30 OAc,H, 3.10;CH20Ac,H,6.17;C0,Me,H, 10.5;Ph,H, 13.8;Ph,Me, 16.6;Me,C02Me,24.0;Me,CN, 33.2 H, 8.0;Me, 46.5;Et,43.5;Br, 23.2;C1,22.7 H,32;Me, 141;Et, 138;Br, 70;C1, 77 H,81;Me, 333;Et, 300;Br, 151;C1,163 F, .0138;C1, .301;Br, .676;H, 1.000;Me, 14.5;Et, 19.7;F,F, ,012; Me,Me, 286 F, .0190;C1, .265;Br, ,622; H, 1.000;Me, 9.20;Et, 14.1;F,F, .015; Me,Me, 151 F, .0242;C1, .235; Br, 5 8 8 ; H, 1.000; Me, 6.41; F,F, .0182;Me,Me, 90.1 F, .000276;Cl, 2.03;Br, 1.86;H, 1.00;Me,4800;Et, 1430;F,F, .000645; Me,Me, 825,000 Ph, 17; BuO, 3.9; CO,Me, 2.04; CH,OH, 1.5; C,H,,, 1.00; PhCH,, .99; OAc, .81; CH,CI, .72; CH,OAc, .59;CH,CN, .37 C,H,, 158; Ph, 123; Ac, 424;CN, 308; CO,Me, 164;C1,7.2; OAc, 2.2; OEt, 1.4; CH,CI, 4.0; CH,OAc, 1.4 CO,Me, 237; CN, 410;CH,Cl, 5.6; CH,OAc, 1.7 Ph,2.9x105;CN,4.8x10S;C0,Me,2.6x104;C1, 1.3x104;OAc, 2.9 x lo3;OEt, 980; CH,OAc, 4900 C,H,, 774; Ph, 821; CN, 286; C1,30; OAc, 19;CH,Cl, 4.3; CH,OAc, 16.8 C,H,,2 x1OS;Ph,5 xl0';CO,Me,2090;C1,232;OAc,279;OEt, 695; CH,OAc, 418 MeO, .89; Me, .48; H, 0; C1, -1.47 MeO, .80; Me, .48; H, 0; C1, -1.40 MeO, .30; Me, 0; MeOCH,, -.55; H, -1.42 MeO; .38; Me, 0; MeOCH,, -.60; H, -1.80 CI, .019; H, .19; Me, .57; Et, 1.15; i-Pr, 2.2; t-Bu, 5.6; OMe, 1.9 CI,CI, .0009; Cl,H, .19; Cl,Me, .12; H,H, -.19; H,Me, .57; Me,Me, 2.0; H,OMe, 1.9 OMe, ,000841; Me, ,000227; Ph, .0000428; H, .0000683 Me,Me, .000336; Me,H, .000154; H,H, .0000683 ;Cl,H, .00000690 Me,Me, 240; Me,H, 15; Me,Cl, 1.5; H,C1, .002 Me, 23.O;Ph, 183;C1, 1.08;CF3, .326;CN, .147;Me,, 36.2 Me, 1.20;Ph, 5.67;C1, .02;CF,, .314;CN, ,055; Me,, 36.2 Me,2.68;Ph, 37.0;C1,2.07;CF3, 19.5;CN,23.2;Me2, 3.43
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 197 Set 15-66 15-67 15-68
15-69 15-70 15-71
15-72 15-73 15-74 15-75 15-76 15-77 15-78 15-79 15-80 15-81 15-82 15-83 15-84 15-85 15-86 15-87 15-88 15-89 15-90 15-91 15-92 18-1 18-2
18-3 184
Ref.
Data Me, 1.15;Ph,9.2;Cl, .309;CF,, 15.9;CN,4.42;MeZ,3.43 PhSO,,PhSO,, .29; Bz,PhSO,, ,727; Bz,Bz, .0384; Ac,Ac, .009; CN,CN, .00328; CO,Me,CO,Me, .00268; CO,Et,CO,Et, ,0024; CO,H,CO,H, .00222; CO,Me,H, .0000622; CN,H, .0000475 PhSO,,PhSO,, ,00656; CN,CN, .00318; Bz,PhSO,, .000258; Bz,Bz, .000257; CO,Me,CO,Me, .0000328; CO,Me,H, .0000622; CN,H, .0000475 PhSO, ,PhSO, , .115 ; PhSO,,Bz, ,0275 ; Bz,Bz, .O136; CN ,CN, .000806; CO,Me,CO,Me, .000724; CO,Me,H, ,0000118; CN,H, .0000104 PhSO,,PhSO,, .00194; CN,CN, ,00091; Bz,Bz, .0000666; CO,Me, CO,Me, .00000628; CO,Me,H, .0000118; CN,H, ,0000104 CN,CN, .0453; CN,CO,Me, .0084; CO,Me,CO,Me, ,00215; CO,Et,CO,Et, .00160; CN,H, .00145; CO,Me,H, .000718; Ph,H, .00007; Ph,CO,Me, .00002; Me,CO,Me, .000005;Me,CN, .000011 CN,CN, .0435; CN,CO,Me, .0042; CN,H, .00145;CO,Me,CO,Me, .0000205; CO,Me,H, ,000718; Ph,H, .0007 CN, .0084; CO,Me, .00215; H, ,000718; Ph, .00002; Me, .000005 CN, .453;CO,Me, .0084; H, .00145; Me, .000011 Bz,Bz, ,0144; PhSO,,PhSO,, .0106; Bz,PhSO,, ,00772; CN,CN, .000224 Bz,Bz, 1.94; PhSO,,PhSO,, 12.8; Bz,PhSO,, 4.13;CN,CN, 19.4 Me,CO,Me, .000148; Me,CN, .000205; CN,H, .00145; CO,Me,H, ,000718; Ph,H, .00007 OBu, .00604; 0-i-Bu, .00598; Ph, ,002; CO,R, .0005; 4-MeC6H,, .0026 Ph, 3.5; CHO, 1.8; CO,Me, 2.0; CO,Et, 1.9;CN, 2.2; Ac, 2.3; NO,, 3.7 CN, ,211; MeO,C, .688;OAc, .945; Br, .730; C1, .879;Ph, 1.60;Me, ,374 CN, .184; MeO,C, .192; OAc, .15 1 ;Br, ,349; CI, .319; Me, 1.82 CO,Et, 9.85; BuO, .40; Ph, .40; BuCH,, .24; CN, 1.07 H, 9.85; CO,Et, 8.36; Me, .27; Ph, ,095 EtO, 29,200; Ph, 105; PI, 101; nC,H,,, 66.6; OAc, 12.9; CH,CO,H, 5.15 EtO,C, 66; BuO, 15;Ph, 9.3; Bu, 2.6 EtO,C, 48;Ph, 1.60; EtO,CCH,CH,, .19; BuCH,, .137; CH,OAc, .46; OBu, .31; Vi, .7a H,48;Ph,2.8;Me, I.OO;Me,N, .27;C02Me,287 , C1,57; CH,CO,Me, 39; H, 48; Me, 17 PhO,C, 2500; EtO,C, 707; CN, 434; Ph, 1.40 CO,Me, 384; Ph, 11.7; AcOCH,, 7.25; MeO,CCH,CH,, 3.75; BuCH,, 2.64; CN, 279; CO,Et, 399 Me,CO,Et, 3.77; Bz,Bz, 327; CN,CN, 166; CO,Et, CO,Et, 72.5 Me,CO,Et, 32.5; Bz,Bz, 2380; CN,CN, 1280; CO,Et,CO,Et, 604 Table 18 Me2N,9.12;NH,, 10.20;Me, 10.21; Et, 9.98;Pr,9.86;Bu, 9.82; F,11.40;H,10.87;OH, 11.05;OMe,10.82;OEt, 10.61 ” Me,N, 8.81;NH2,9.71;CH,C1,9.71;Me,9.69;Et,9.53;Pr,9.39; 10.21;Ac,9.23;OH, 10.35;OMe, Bu,9.17;Cl, 11.02;Br, 10.55;H, 10.27; OEt, 10.10 ” Me, 9.53; Et, 9.32; H, 9.98; OH, 10.24; OMe, 9.87; OEt, 10.00 ” CH,Cl, 10.20; CH,Br, 1O.13;CCl3, 10.44; Me, 10.10; Et, 10.00; H, 10.61
MARVIN CHARTON
198 Set 18-5 18-6 18-7 18-8 21-1 21-2 21-3 214 21-5 21-6 21-7 21-8 21-9 24-1 24-2 24-3 244 24-5 24-6 24-7 24-8 24-9 24-10 24-11 24-12 24-13 24-14 24-15 24-16 24-17 24-18 24-19 24-20 24-21 24-22 24-23 24-24 24-25 24-26 24-27 24-28 24-29 24-30
Ref.
Data CF,,10.25; Me,9.27; F,10.6;C1,10.6; H,10.87;Ph,9.45 ” CF3,11.81;Me,9.69;Et,9.32;Bu,9.l0;CI, 11.78;H, 10.87;Ph,9.45 ” OH.1637;OMe,1631;OEt,1635;C1,1609;H,1618 ” OH,1638;OMe,1639;0Et, 1637;C1,1634;H,1648 Table 21 Me,3.58;OH,3.14769a; OEt,3.25;OMe,3.35;0-, 5.39573b; NH,, 3.717 3.64;PhNH, ’’ Me,4.60; Ph,4.65;OH, 4.52a; OEt,4.52;OMe,4.49; 0-, 5.40b; NH,, 4.54;PhNH,4.701 ” Me,4.67;OH,4.64a; 0-, 5.12b;NH,,4.60 ” Me,4.72; OH,4.74a; OEt,4.60;0-, mb; NH,.4.63 ” i-Pr, 3.05;Ph,2.82;HCNOH,2.55 H,3.00; Me,3.38;Et,3.20; ” OEt,3.66;NH,,3.8788;Et,3.7164;H, 3.43;Me,3.6671;CICH2, 3.38; Ph,3.66 ” Me,2.95;Me,N,3.35;EtO,3.08;EtS,2.94 ” 4-O,NPn, 4.2; ClCH,,4.5;Ph,6.0; 2-PhVn, 6.1;Me,6.6; 4-MeOPn, 6.7;Me0,8.8;EtO,8.95;H2N, 11 ” CICH,,.130; Ph,1.21;2-PhVn, 2.80;Me,7.65;MeO,145;EtO,155; H,N,100 Table 24 MeS,5.85;EtS,6.049;PhS,4.481;MeO,5.68;EtO,6.37;Ph,7.00;A NH,,11.9 Ph,308;Me,198;EtO,CCH,,385;CCl,,770;4-0,NC,H4, 441 Me,157.2;Pr, 123.8;Et,134.5;Ph,97.l;CH2C1,45.7 Me,70.1;PI,52.3;Et,55.1;Ph,40.2;CHZC1, 21.8 Me,126.5; PI,80.4; Et,93.6; Ph,81.8;CH,CI,31.8 Me,51.5;Pr,35.2;Et,38.9;Ph, 37.5;CH2C1, 14.4 Me,59.0;Pr,45.5; Et,44.0;Ph,34.8;CH,Cl,21.0 PI,22.3;Et,20.2;Ph,18.6; CH,Cl,12.0 Me,25.9; Me,41.8;Pr,35.1;Et,33.3;Ph, 30.2;CH2C1, 14.8 Me,18.5;Pr,16.7;Et, 15.4;Ph, 15.4;CHZCl, 8.0 Me,135.0;Pr, 129.1;Et,122.1;Ph,102.6;CH,CI, 47.7 Me,60.1;Pr,50.7;Et,52.6;Ph,40.8;CH,C1,22.1 Me,112.7;Pr, 81.9;Et, 79.4;Ph,84.6;CH2Cl, 32.3 Me,43.7;Pr,35.4;Et,33.0;Ph,34.8;CH,CI,15.8 Me,176.7;PI,112.2; Et,104.8;Ph,106.0;CH,CI,42.5 Et,45.6;Ph,41.5;CH,CI,18.7 Me,71.7;Pr,44.6; 109.0;CH2C1, 31.3 Me,173.7;Et,lOl.O;Ph, Me,78.5;Et,41.8;Ph,44.0;CH2C1, 16.1 Me,134;Et,107;H,64;CH,CI,38;CCl,,32 MeS,3.7;MeO,5.1;Ph,8.1;Me,12.0;Me2N, 16.0 MeS,3.0;Me0,3.8;Ph,6.5;Me,8.7;Me2N, 11.0 MeS,2.5;MeO,2.9;Ph,5.0; Me,6.4;Me,N,7.7 MeS,.93;MeO,.97; Ph,1.48;Me,1.72;Me,N,1.91 MeS,34;MeO,.89; Ph,1.22;Me,1.40;Me,N,1.55 MeS,.77;MeO, .82;Ph, 1.15;Me, 1.21;MeZN, 1.31 Me,6.4;Et, 6.4;H,6.1;CH2C1,4.7;CC1,, 3.8 CF,,3.6;Me2N,6.0;Me, 6.1;Ph, 5.2 OMe,3.3;SMe,3.2;NMeZ,6.1;Me, 3.7 CF,,185;Me,N,338;Me,342;Ph,283 OMe,170;SMe,162;NMe,,342;Me,193 ”
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 199 Set 24-3 1 24-32
Ref.
24-33
”
24-34 24-35 24-36 24-37 24-38 24-39 2440 2441 2442
”
2443 2444 2445 2446 24-47 24-48 27-1 27-2 27-3 274 27-5 2 7-6 30-1 30-2 30-3
30-4 30-5
30-6
”
Data Me,N, 183; EtO, 152; Et, 160; Me, 160; Ac, 87a; Ph, 152 ClCH,, 57; Ac, 4Sa; Bu, 84; t-Bu, 77; Me,N, 123;i-Bu, 77; BuCH,, 77; Ph, 77; EtO, 84; Et, 77; Me, 97 Me,N, 117; 2-MeVn, 97; Ph, 84; Bu, 117; 2-PhVn, 90; 2-furyl,70; i-AmO, 70 Me, 84; ClCH,, 70; EtO,C, 32a, EtO, 49; 2-furyl, 77 Et, 77; MeO, 84; Pro, 70; i-Pro, 74; BuCH,, 84; Me, 77 MeO, 49; C1,35; Et, 84; Ph, 63 Me, 2600; i-PI, 2300; Bu, 2400; ClCH,, 1500; CL,CH, 900; Cl,C, 650 Et,3.9;Me,6.8;H,2.9;CHZCl, 1.3;CC13,.3;Ph, 3.8
”
Et,4.0;Me,3.9;H,3.7;CH,Cl,3.3;CCl3,2.5
” ”
” ” ”
OMe, .52; SMe, .72; Me, .85; NMe,, 6.9 H, 19;Me, 61;Et,2l;Cl, .13;ClCH,, l.l;Cl,CH, .45;OEt, 10.5 ” Et, 16.82; i-PI, 16.37; t-Bu, 13.03; CH,Cl, 12.80; CHCl,,9.35; CCl,, 3.05; Me, 17.08; Pr, 16.76; H, 17.00; EtO, 15.98 ” Et, 3.0 x lo6;i-Pr, 8.8 x l o 5 ;t-Bu, 2.3 x 10,; CH,C1, 4.9 x 10; CCl,, 1.7 ” Me, 27.80; Me,N, 29.64; EtO, 22.37; CF,, 16.58;C1,17.22 ” Me, 16.38; Et, 16.23; MeO, 15.17; t-Bu, 12.83;CF3, 2.7 ” Et, 16.53;i-Pr, 16.16; t-Bu, 14.58; EtO, 16.82;Cl, 3.3;MeO, 16.23 ” Me, 17.03; Et, 17.43; PI, 17.50; i-Pr, 17.07; t-Bu, 16.95; Me,N, 27.80; MeO, 16.38 ” Et, 162;i-P1, 155;t-Bu, 137;CH,C1, 150;CHCl,, 116;CC13,74;Me,160 Table 27 3-PnNO,, 10.16;4-PnNOZ,9.96;4-PnNMe2, 11.25; 2-furyl, 10.85; Ph, 10.68; 3-MeOPn, 10.59; 4-MeOPn, 10.92; 2-PhVn, 10.55; Bz, 8.30; CO;, 10.23 ” Me, 12.42;Ph, 11.35;Ac,9.30;Et, 12.45;Bz,9.25;NOZ,7.4 ” 4-O,NPn, 10.47;Ph, 11.18;H, 11.33;Bz,8.80;Ac, 8.85;CO;, 30.95; CO,Me, 8.87; CO,Et, 8.95; CONH,, 9.55 ” Ph, 11.33; 3C6H4N0,, 10.74; t-PhC,H,, 10.89; 2-f~1yl,11.16; 2-thienyl, 10.76; ~ z C ~ H11.60 ,~, ” H, 8.30; Me,9.30; Et, 9.38; i-Pr,9.50, Ac, 7.38; CO,Et, 1.01 ” 4-O,NPn, 10.85; Ph, 11.18; H, 10.68; Me, 11.35; CO;, 11.63; CONH,, 10.1; Bz, 10 Table 30 Ph, 11.6; MeS, 9.83; Me, 12.41; MeO, 9.72; NH,, 13.86; EtO, 10.021; BuO, 10.146; Pro, 10.155; Me,N, 13.4; CH,=CHCH,O. 9.70 ” H,N, 10.770; PhNH, 10.42; MeO, 7.41;MeS, 7.14 ” OH, 3.90309a; H, 3.7857; Me, 4.7807; Et, 4.8948; Pr, 4.8060; i-Pr, 4.8248; t-Bu, 5.0155; CO;, 3.89963b; CH,Cl, 2.8159; CH,OH, 3.8748; NH,, 5.74 ” OH, 4.108a; Me, 4.7696;Et, 4.8844; PI, 4.8030; AcNHCH,, 3.6816; MeOCH,, 3.5381; NCCH,, 2.44466; H, 3.7719;CO;, 3.9340Sb ” OH, 4.055Sa; Me, 4.7582; Et, 4,8742; Pr, 4.8044; CH,CI, 2.8447; CH,Br, 2.87514; CH,I, 3.1433; CH,AcNH, 3.6726; CH,CN, 2.4523l;CH2OMe, 3.5505; H, 3.7572; CO; 3.95468b; Ph, 4.214 ” H, 1.79 x 10-4;Me, 1.734 x lO-’;Et, 1.32 x IO-’;Pr, 1.53 x lo-’; i-Pr, 1.44xlO-’;Bu, 1.51 xIO-’;i-Bu, 1.70~10-’;r-Bu,9.4 x 1 O V 6 ; truns-2-MeVn, 1.95 x lo-’; ViCH,, 4.8 x CICH,, ICH,, 7.0 x 10-4;Cl,CH, 5.83 x lo-’; 1.49 x lo-’; BrCH,, 1.29 x HOCH,, 1.46 x 6.09 x 1.42 x 1 0 - ~ b ” ”
MARVIN CHARTON
200 Set 30-7
Ref.
30-8
30-9
30-1 0
30-1 1 30-1 2
30-1 3 30-14 30-1 5 30-16 30-1 7 30-1 8 30-1 9 30-20 30-2 1 30-22 30-23 30-24 30-25 30-26 30-27
‘
Data CCI,, .217; Me, 1.753 x IO-’;Et, 1.338 x 10-5;Pr, 1.592 x lo-’; CH,F, 268.4 x IO-’;CH,Cl, 139.4 x 10-5;CH,Br, 129.63 x lo-’; CH,I, 69.46 x IO-’;CH,CN, 346.94 x lo-’; MeOCH,, 27.60 x lo-’; Ph,6.13 xIO-’;H, 17.65 xlO-’;C,H, 1.359 x I O - ~ ; C O ; , 1.134 x H, 3.7515;Me, 4.7560;Et,4.8742;Pr,4.8l96;Vi,4.255;ViCH2, 4.3521;C1CH2, 2.8668; BrCH,, 2.90205; ICH,, 3.1752; HOCH,, 3.8309; PhCH,CH,, 4.6644; PhCH,, 4.3074; Ph, 4.2050; NCCH,, 2.47011;HCZ, 1.84. frans-2-PhVn, 4.438;Me3SiCH,, 5.22;C02H, 1.571 ;CO;, 3.96Sb;’CF,, -.26; OH, 4.06550; NHAcCH,, 3.6698; CH,OMe, 3.570; r-Bu, 5.03; CCl,, .635 OH, 4.1 19a; Me, 4.7570; Et, 4.8775; Pr, 4.8286; CH,Cl, 2.88342; CH,Br, 2.91800; CH,I, 3.1934; CH,CN, 2.481 78; CH,AcNH, 3.6731 ; CH,OMe, 3.5834; H, 3.7525; i-Pr, 4.8857; r-Bu, 5.04048; CO;, 4.00700b; CO,H, 1 .56a OH, 4.0783a; Me, 4.7625; Et, 4.8827; Pr, 4.8419; CH,CI, 2.89983; CH,Br, 2.93599; CH,I, 3.2128; CH,NHAc, 3.6779, CH,CN, 2.49550; CH,OMe, 3.5996; H, 3.7577; CO;, 4.0296Sb; CO,H, 1.57268a OH, 4.0969a; Me, 4.7773; Et, 4.9007; Pr, 4.8706; CH,AcNH, 3.6945; CH,CN, 2.5281 2, CH,OMe, 3.631 3; H, 3.7734; CO;, 4.0872Sb; Ph, 4.241 Me,5.28;t-Bu,5.52;PhCH,,4.79;H,4.21;HOCH,,4.26,ICH,, 3.61; BrCH,, 3.46;C1CH2, 3.33. FCH,, 3.13; NCCH,, 2.94; Ph, 4.71; CO,H, 1 .967a; CO;, 4.49d Ph, 6.63; i-Bu, 7.33; cyclohexyl, 7.47; HOCH,, 5.78; H, 5.61; CH,C1, 5.04; PhCH,, 6.73; I-Bu, 7.76; rrans-2-PhVn, 6.68; PhCH,CH,, 7.03 H, 11.15;PhCH2, 10.34;Ph. 10.43;CH,C12,7.28 H, 8.92; Me, 10.57; ClCH,, 8.48; CH,CH, 7.07; CI,C, 5.32; Ph, 10.92 H,9.02;Me, 10.68;C1CH2,8.60;CI,CH, 7.19;C13C, 6.04;Et, 10.89; Ph, 11.34 CHCI,, 2.60;CHZCI,4.74; Ph, 6.27;Et, 7.18; r-Bu, 7.43 CCl,, 1 .OO;CHCl,, 2.00; CH,CI, 3.97; H, 4.74 CCI,, .443;CI,CH, :016;CH2C1, 9.0 x 10-4;Me, 3.3 x H, 9.2 x lO-’;Ph, 5.8 x CCI,, 2.26; CHCI,, 2.54; CH,CI, 4.54; H, 5.05; Me, 5.85 H, 8.64;Me, 10.03;C1CH2,8.31;C1,CH, 7.41;C13C,6.26,Et, 10.07; Ph, 9.79 CI,C, .70;CHCI,, 1.75;CH2C1, 2.80;H, 3.64;Ph,4.58;Me, 5.18 t-Bu, 112; Bu, 83; i-Bu, 70; Et, 43; Me, 20; PhCH,, 16; CICH,CH,, 1.8; ClCH,, .14; Ph, 52 r-Bu, .30103; Et, .32; Me, .38; PhCH,, .45; HOCH,, .75; H, .66; Lh CH,CI, .83 I-Bu, 1.497;Et, 1.449;Me, 1.423;PhCHZ,1.30103;Ph, 1.182; HOCH,, 1.137; H, 1.217;CH2C1, .73;CH,CN, .58 CCI,, 11.0;CHCl,,4.07;NCCH,, 2.77;C1CH2, 2.12; H, 1.06;Ph, 1.80;Me, 1.06;r-Bu, 1.11 Me, -3.28;CICHaCH,, -2.63; H, -2.29; CH,Cl, -1.62, CHCI,, -.21, CCI,, .I76
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS Set 30-28 30-29
33-1 33-2 33-3 3 3-4 3 3-5 3 3-6 33-7 33-8 33-9 33-10
33-1 1 33-1 2 33-1 3 33-14 33-15 33-16 33-1 7 33-1 8 33-1 9 33-20 33-21 33-22 33-23 33-24
33-25
Ref.
201
Data
Me, 4.26; Ph, 5.43; CH,C1, 47.6; CHCl,, 190; CCl,, 501 NCCH,, 18.5; CICH,, 12.9; HOCH,, 3.01; H, 2.23; ClCH,CH,, 2.24; PhCH,, 1.47; PhCH,CH,, 1.09; Ph, .96; Me, .463; BuCH,, .442; t-Bu, .296 Table 33 Br, O;CI, .44;F, .75;Me, -.75;CF,, 2.36;CN, 3.6;Ph, -.84; t-Bu, -.661; H, 0 Br, .86;CI, 1.1 1 ; I, .55; H, .72; CO,H, 2.31; CHO, 3.39; CO,Et, 2.21; CN,4.55;Ph,O;Vi,.27;Ac, 3.26 H, -.88; C1, I .24; Br, 1.07; 1, .76; CN, 4.24; Ac, 3.2 H, .87;C1, 1.28;Br, 1.06;1, .81;CN,4.25;Ac,3.2 I, 4.59; Br, 3.88; H, 3.6; Ph, 4.55; Bu, 4.24; BuCH,, 4.25 ?-Bus, 910; MeO, 63; t-Bu, 2.1; ViS, 4000 t-Bus, 64; MeO, 15; t-Bu, .8; ViS, 430; ViO, 60 Ph, 6.6; H, 4.8; Bu, .38; MeO, 13: Ph,Si, 450 BrCH,, 430; ClCH,, 390; ICH,, 265; Ph, 250; Me,Si, 66; PhCH,, 25; i-F'r, J2.3;n-Bu, 9.7; BuCH,CH,, 9.4; t-Bu, 8.9; neopentyl, 7.0 ClCH,, 3318; 4-MeOPn, 3323; Ph, 3323; 4-02NPn, 3319; Bz, 3306; EtO,C, 3310; EtO, 3339; BrCH,, 3316; BuCH,CH,, 3319 ClCH,, 3317;Ph, 3320; Bz, 3304; EtO,C, 3309;BrCH,, 3315; BuCH,CH,, 3317 CICH,, 3250; Ph, 3250; Bz, 3219; EtO,C, 3320; BrCH,, 3250; BuCH,CH,, 3267 Bu, 74;Ph,91;C1CH2,94;Me0, 81;EtO,C, 123;BrCH,,94;BuCH2, 74; BuCH,CH,, 72 Bu, 3314;Ph, 3314;ClCH,, 3314;MeO, 3328;EtO,C, 3306;BrCH,, 3313;BuCH,, 3314;BuCH,CH,, 3314;CN, 3304 ClCH,, 3.90; BrCH,, 3.45; EtS, 4.20; MeOCH,, 3.90; EtOCH,, 3.30; BuCH,, 3.90; CN, 6.60 ClCH,, 4.80; BrCH,, 4.50; EtS, 5.70; MeOCH,, 4.50;EtOCH2, 4.20; BuCH,, 4.65; CN, 7.80 CICH,, 6.90; BrCH,, 6.60; EtS, 7.80; MeOCH,, 6.00; EtOCH,, 5.70; BuCH,, 6.30; CN, 10.5 CICH,, 24.60; BrCH,, 24.20; Et, 24.60; MeOCH,, 20.70; EtOCH,, 20.40; BuCH,, 18.60; CN, 43.6 CICH,, 24.30; BrCH,, 24.30; EtS, 22.20; MeOCH,, 20.70; EtOCH,, 19.50; BuCH,, 17.40; CN, 46.6 CICH,, 21.60;BrCHZ, 21.60;EtS, 21.60; MeOCH,, 19.80;EtOCHZ, 19.50;BuCH2, 17.10;CN, 35.8 ClCH,, 34.20; BrCH,, 33.60; EtS, 34.80; MeOCH,, 30.30; EtOCH,, 29.15; BuCH,, 27.10 ClCH,, 46.85; BrCH,, 46.20;EtS, 40.20; MeOCH,, 34.50; EtOCH,, 32.45; BuCH,, 28.50 CiCH,, 47.05; BrCH,, 46.10; EtS, 47.10; MeOCH,, 37.25; EtOCH,, 36.95; BuCH,, 35.70 Me, -1.76;Pr, -1.79;Bu, -1.73;CHO, -1.89;CH2OH, -2.33; CH,I, -2.19; CH,Br, -2.33; CH,CI, -2.40, Vi, -2.92; Ph, -2.93; EtS, -2.64; EtO, -1.33 H, 1S O ;Me, 1.56; Et, 1.59; HC,, I .48; Pr, 1.72; I-Bu, 1.75; CHO, 2.75; Ac, 3.00
MARVIN CHARTON
20 2 Set 33-26 33-27 33-28 33-29 36-1 36-2 36-3 36 4 36-5 36-6 36-7
36-8 36-9 36-10 36-11 36-12 36-13 39-1 39-2 39-3 39-4 39-5 39-6 39-7 39-8 39-9 39-10 39-1 1 39-1 2 39-13 39-14 42-1
Ref.
Data Me, 1.76;Et, 1.78;HC2,2.01;Pr, 1.75;t-Bu, 1.87;CHO,3.28;Ac, 3.03 ” H, 12.97;Me,2.423;Cl, 14.28;Br, 13.96;Et,2.49;Bu,2.50;t-Bu,2.21; Ph, 5.88;COZH,35.3Sa; CO;, 7.10b ” H, 4.68; Me, S68; C0;,2.40; CO,Et, 34Sa ” H, 18; Bz, 135; CO,Et, 99; Ph, 3.0; Me, 1.9 Table 36 H,2.986;Me, 392;CI,2dO;CN,O;Br, 2.94;F, 1.68;1, 3.71;CC13, 1.93;C2H,3.6; t-Bu, 3.65;Ph,4.14 ” Et, 2265.0; i-Pr, 2264; t-Bu, 2254; CICH,, 2266.0; Me, 2267.0; Br, 2196.0 ” Me, 2252.5; Et, 2247.2; i-Pr, 2245.3; t-Bu, 2234.5;CICH2, 2260.4; Br, 2185.1 ” Me, 2255.0; Et, 2249.2; iPr, 2247.4; t-Bu, 2235.8;C1CH2, 2260.4; Br, 2188.4; I, 2168.1 ” Me, 2255.4; Et, 2249.6; iPr, 2247.8; t-Bu, 2236.6; CICH,, 2260.7; Br, 2187.8; I, 2168.2 ” Me, 2255.7;Et, 2249.9;i-Pr, 2246.5;t-Bu, 2235.3;C1CH2, 2261.4;Br, 2188.5; I, 2166.6 ” t-Bu, 169; PI, 167;iPr, 166; Bu, 165; Et, 165; Me,Si, 165; truns-2-PhVn, 165; Me, 159; PhCH,, 158; ViCH,, 155; Ph,C, 155; Ph,CH, 154; Ph, 153;Vi, 143;PhC,, 123;C1CH2,ll7;1,114;Br, 102;CI,CH, 84;Cl,C, 62 ” t-Bu, 85; Pr, 82; i-Pr, 84; Bu, 85; Et, 81 ; trans-2-PhVn, 82; Me, 78; PhCH,, 78;ViCH,, 74;Ph,CH, 74;Ph, 73;Vi,68;C1CH2, 51 ” Me, 160;Pr, 164;Vi, 145;Br, 102;ViCH,, 150 ” Me, 18.2;CICH2,4.38;C1,CH, l.lS;Cl,C, .49 ” Me, 12.4; CICH,, 3.55;CI2CH, .82; CI,C, .39 ” Me, 8.39;CICH1, 2.41;CI2CH, .69;C13C, .20 ” Me, 4.58. CICH,, 1.23;Cl2CH, .46;C13C, .15 Table39 Ph,.49;Ac,2.84;H,O;Et,-.18;CI,1.76;CN,3.76;Pr,-.75;Br, 1.69 Me,9.88;Cl, 10.10;CN, 11.2;H, 10.23 ” ” CN, 1.624; COCI, 1.624; CO,H, 1.626;C02Et,1.627; Bz, 1.628; Ac, I .628; NH,, 1.632; H, 1.6345; Ph, 1.635; CH,OH, 1.637; PhCH,, 1.638; Bu, 1.639; Et, 1.639 ” CN, 1.625; CO,Me, 1.628;CO,Et, 1.627; Ac, 1.629; COCl, 1.624; CH,OH, 1.638; Ph, 1.634; CHi4, I .690 ’’ CN, 2.216;C02Me, 2.224;CO1Et, 2.221; Ac, 2.226;COCI, 2.219; CH,OH, 2.228; Bz, 2.225; r>-CH,, 2.231 w CN, 1.626; COCl, 1.627;CO,H, 1.628; CO,Et, 1.629; Bz, 1.629; NH,, 1.633; H, 1.635; Ph, 1.636 ” CN, 1.632; Bz, I .636; CH,OH, 1.644; Me, 1.647 ” H,4.83;CI, 3.26;COZH,2.12”,CO;, 5.13b ” Ph, 4.50; cyclohexyl, 4.79; CO, H, 3.9Sa; CO,, 4.83b; PI,, 5.04; Ph,, 4.51; Ph, Me, 4.73; H, 4.83 ” i-Bu, 7.90;Ph, 7.42; Gi-Pr, 7.55;CO;, 7.77b; CO,H, 6.3Ia ” H, H, 4.30; Me,H, 47.5; Me,Me, 533; EtO,H, 4030 ” H, .026; cyclopropyl, 191; Vi, 30.8; Et, 9.40 ” Me,C=CH, 8.09; i-Bu, 8.24; Ph, 8.1 1; i-Pro, 8.30 ” H. .026; cyclourouyl. 9.87;.~Vi. 2.67;. Et.. .464 Table 42 Ph, 193.; Vi, 184; CHiCl, 164; CH,Br, 171;Me, 220; Mea, 257 ”
SUBSTITUENT EFFECTS IN NONAROMATIC UNSATURATED SYSTEMS 203 Set 42-2 45-1 45-2 45-3 45-4 45-5 45-6 45-7 45-8 45-9 45-10 45-1 1 45-12 45-1 3 45-14
Ref.
Data Ph, 2.9; Vi, 3.9; CH,Cl, 2.0; CH,Br, 2.2; Me, 5 . 5 ; Me,, 13.0 Table45 H, 10.5;CO,NH,,9.3;CN,7.35;NO,,7.0 H, 11.70; Me, 12.01; C1, 9.87; I, 9.93; Br, 10.03; NO,, 7.97 H, 11.70;Me, 12.59;C1,10.40;Br, 10.42;N01, 8.52 Br, .715 1;C1, .7125; H, .6990; Me, .6454 H, .699;Me, .645;C1, .713;OH, S96; Br, .714 H, 696; Me, .641; C1, .710; OH, 593; Br, .7 10 H, 703.5; C1,721 ;Me, 640.5; Et, 636; Vi, 667 ”
H,-.Sl;Me,-.58;Ph,-.50;C1,-.34 H,-1.14;Me, -1.lO;Ph,-1.03;C1,-.92 H, .711;C1, ,734; Br, .737; I , .737; Me, .653;Et, .650;OH, .600;MeO, ,642; Ph, .698 Me,Me, .5093; Cl,CI, .7230; Br,Br, .7228; Cl,Me, .6542; Br,Me, .6564 Me,Me, .600; Cl,Cl, .740; MeO,MeO, ,476; EtO,EtO, .479 H,H, .71 I ; Me,Me, S97; Me,i-Pr, .589;Cl,Cl, .734;MeO,MeO, .459; EtO,EtO, .479 H,H, -.57; Me,Me, -.67; Cl,Cl, -.18; f-Bu,t-Bu, -.71; SiMe,,SiMe,, -.51
45-15 45-1 6 45-1 7
45-1 8 45-19 45-20 45-21 45-22 45-23 45-24 45-25 45-26 45-27 45-28 45-29
45-30 45-3 1 45-32 45-33 45-34 45-35
H,H, .71 I ; Cl,Cl, .746; Br,Br, .768; Me,Me, .604; Me,i-Pr, S97; PhO,PhO, .633; Ph,Ph, .689 H,H, .711; Me,Me, .607; MeO,MeO, .612; Cl,Cl, .740;Br,Br, .744; I,I, .746 H,H,H,H, -.31; Br,Br,Br,Br, -.16; CI,CI,Cl,CI, -.ll;CI,CI,CN,CN, .25 H,H,H,H, .711; Me,Me,Me,Me, .466; CI,CI,CI,Cl, .703; OH,CI,OH,CI, .422; OH,Br,OH,Br, .418 H,H,H,H, 703.5; Cl,Cl,CI,Cl, 716.0; Cl,Me,Me,Cl, 615.0; Me,Me,Me,Me, 462.8 H,H,H.H, - 5 1 ;Cl,Cl,Cl,Cl, .01;Br,Br,Br,Br, .OO;Cl,Cl,CN,CN, .51; F,F,F,F, -.04; Me,Me,Me,Me, -.84 H,H,H,H, -I.l4;Cl,Cl,Cl,Cl, -.71; Br,Br,Br,Br, -.72; Cl,Cl,CN,CN, -.30; Me,Me,Me,Me, -1.45 H, 235; Me, 190; C1,285; Br, 280 C1, -271; H, -222; Et, -203; NHAc, -199; Me, -190; OMe, -159; OEt, -153; NMe,, -1 10; NH,, -58;OH, 62; CH,OH, -219 H, -222; NHAc, -390; Me, -341; NH,, -305; OMe, -287 H, 795; Me, 748; C1,804, MeO, 741; BzO, 796 H, 741; CO,H, 822; CHO, 807; Ac, 797 H, 710; Me, 658; C1,705; Br, 720 Me,Me, 710;H,H, 795;CI,Cl, 813;CN,CN, 903 H, 795; Me, 753; C1,801; f-Bu, 732; Ph, 778; HO,C, 833; MeO,C, 869; CHO, 872; Ac, 857; NO,, 891; MeO, 676; BzO, 803; MeO,CC,H,, 807; EtO,CC,H,, 808; HOCH,C,H,, 752 H, .833;C1, .810; Br, .810;Me, .796 C1,738; ViCH,, 696; Ac, 821; CHO, 839; CO,Me, 820; CO,H, 779; H, 741; MeOCC,H,, 754; EtO,CC,H,, 758 Me,Me, 710; CI,Me, 765; H,H, 795; CI,Cl, 824 MeO,MeO, 735; Cl,CI, 818; Me,Me, 718; H,H, 795 H,H,H,H, 795; Me,Me,Me,Me, 627; Cl,CI,CI,Cl, 830; Br,Br,Br,Br, 814 H, -124; OH, -294; MeO, -249; Me, -205;C1, -112; NH,, -345; PhNH, -323
MARVIN CHARTON
204 Set 45-36 45-37 45-38
Ref.
45-39 45-40 45-41 45-42 45-43 45-44 45-45 45-46 45-47 45-48 45-49 45-50 45-5 1 45-52 45-53 a
Data H, -278; Me, -346; MeO, -398; NH,, -493; PhNH, -475 H, 488; Me, 422; Et, 419; OH, 362; OMe, 369 H, -4839;OAc, ,4750; NHAc, .4165; Me, .4080;Ph, .4515; NHPh, .2858 OH, -342;OAC, -167;C1, -120;H, -112, NH,, -350;PhNH, -245; AcNH, - 135 OAC, -320; NH,, -505; PhNH, -395; AcNH, -284 C1, -342; OH, -332; NH,, -383; H, -294; PhNH, -324 NH,, .339; MeO, .447; Me, S 4 6 ; NHAc, .560;Ph, .595 NH,, .290; MeO, .440; Me, S50;NHAc, S O ; Ph, .610; C1, .620; CN, .640; CO,H, .600 H, .920; Me, 3 7 5 ; OMe, .809; C1, .927 H, .937; Me, .892;OMe, ,820; C1, .943 H, .9456; Me, .8604;OMe, 3992; C1, 1.006 H, .9255;Me, .8422;OMe, .8737;C1, .9832 H, .9155; Me, .8328;OMe, .8538; C1, .9707 H,H,H,H, 1635; Me,Me,Me,Me, 1637;t-Bu,t-Bu,t-Bu, t-Bu, 1634; Cl,Cl,Cl,Cl, 1646 H, 1675; Me, 1670; Ph, 1667; MeO, 1660; OH, 1663; NH,, 1640; C1; 1684; Br, 1686; NHAc, 1666 Me, 12.42;Et, 12.60;Ph, 11.18;Ac, 7.38;CF3,6.0 H, 9.02;Cl. 2.94; Me, 10.72;NH2, 10.62;Et, 10.67; Pr, 10.81; 2-furyl, 9.80 CO,H, 4.00a; CO;; 4.36b; Me, 4.62; Ph, 4.427
Includes a statistical factor of 1/2. Includes a statistical factor of 2.
Vinyl and Allenyl Cations Peter J . Stang Chemistry Department. The University of Utah Salt Lake City. Utah 84112
CONTENTS I . Introduction . . . . . . . . . . . . . . . . . . I1. Electrophilic Additions to Multiple Bonds . . . . . . . . A . Addition to Triple Bonds . . . . . . . . . . . . 1 . AcidCatalyzed Hydration of Alkynyl Ethers and Thioethers . 2 . Electrophilic Additions to Arylacetylenes . . . . . . 3. Electrophilic Additions to Alkylacetylenes and Acetylene . . B . Electrophilic Additions to Allenes . . . . . . . . . 1. Addition to Allene . . . . . . . . . . . . . 2 . Addition t o Substituted Allenes . . . . . . . . . 111. Vinyl Cations by Multiple-Bond Participation in Solvolysis . . . A . Participation b y Triple Bonds . . . . . . . . . . . B . Participation by Allenyl Bonds . . . . . . . . . . IV. Heterolytic Cleavage of Vinyl Substrates . . . . . . . . A . Vinyl Cations via Diazonium Ions . . . . . . . . . B . Solvolysisof Aryl-SubstitutedVinylSubstrates . . . . . . C . Vinyl-or Cyclopropyl-Substituted VinylSystems . . . . . D . Solvolysis of Simple Alkylvinyl Systems . . . . . . . . E . Structure of Vinyl Cations . . . . . . . . . . . . 1. Theoretical Calculations . . . . . . . . . . . 2 . Experimental Approaches . . . . . . . . . . . F . Rearrangements of Vinyl Cations . . . . . . . . . . 1. Rearrangements to the Double Bond . . . . . . . . 2 . Rearrangements Across the Double Bond . . . . . . G . Kinetic Deuterium Isotope Effects . . . . . . . . . V . Allenyl and Related Cations . . . . . . . . . . . . VI . Miscellaneous . . . . . . . . . . . . . . . . VII . Conclusion and Future Developments . . . . . . . . . References . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
205 207 207 207 210 215 220 220 221 229 229 237 242 254 257 264 269 271 272 274 280 281 284 291 295 311 316 318
I . INTRODUCTION Vinyl cations. la. are carbonium ions where the electron-deficient carbon is part of an unsaturation. with the formally positive carbon bonded to only two substituents. as compared to trisubstituted normal carbonium ions. I b . Although 205
PETER J. STANG
206
ordinary carbonium ions have been known since about the turn of the century (I), vinyl cations have been regarded as unattractive reaction intermediates because of their alleged high energy, and it has been only in the past dozen years that good evidence has been presented favoring the intermediacy of vinyl cations in certain reactions. This chapter will provide a historical and critical review of vinyl and allenyl cation chemistry with emphasis on a mechanistic point of view. >C
=
>"
c"-
Ib
la
A limited amount of information is available on vinyl cations in the gas phase. These mass spectral data suggest that the heat of formation and stability is in between of simple alkylvinyl cations, such as CH2=8H and CH,CH=&, those of methyl and ethyl cations (2). The bulk of the evidence for the existence of vinyl cations comes from mechanistic studies in the liquid phase. Although vinyl cations have not yet been prepared in solution with lifetimes adequate for direct spectral observation, sufficient, increasing evidence has been presented for the existence of such species as transient intermediates. Vinyl cations have been generated in three ways: 1. via electrophilic addition to multiple bonds; a,
R-C=C-R
+Yo
-
0
y,
R-C=C,
-----+
R
2 . via multiple bond participation in solvolysis; RC=CCH,CH,-X
RCH=C=CHCH,CH,X
/
RZPC~
',A -
3. via bond heterolysis in vinyl substrates.
Each of these reactions will be discussed in a separate section (11-IV). Section V will deal with allenyl cations, and Section VII will provide a brief summary and a glimpse at possible future developments.
201
VINYL AND ALLENYL CATIONS
11. ELECTROPHILIC ADDITIONS TO MULTIPLE BONDS
A. Addition to Triple Bonds
1. Acid-catalyzed hydration of alkynyl ethers and thioethers The earliest evidence for vinyl cations as intermediates comes from thorough studies by Jacobs and co-workers and Drenth and co-workers of the acid catalyzed hydration of alkynyl ethers (3-7) and thioethers (8-10). In particular, the hydration of the following compounds has been investigated: RO-Ce-H 2
Et0-M-R 3
RS- C g -H
R = a, n-Bu b , Ph c, Et d, Me e, n-Pr f, i-Pr g, t-Bu
R=a,Me b, Et c, i-Pr d, n-Bu
R = a, Et b, i-Pr C, t-Bu
4
EtS-W-R 5
R=a,Me b, Et c, n-Pr d, t-BU e, D
Hydration of compounds 2, 3, 4, 5 was found to be first order both in substrate and in hydronium ion (4-10). Furthermore, a careful kinetic study of compounds 2c-g and the sulfur analog 4 revealed that the hydration rate at constant ionic strength was dependent on the buffer concentration and hence was general acid catalyzed. The solvent deuterium isotope effect for hydration of 4a and lcH20/kD,o= 1.90, CH3C'-C-OCH=CHCH3 were kH,o/kD,o=2.13 and respectively ( 8 , 6 ) . No deuterium was incorporated at the acetylenic position in 4a when this compound was reisolated after partial hydration in Dz0. In all the above compounds except 2f and 2g, hydration gave the corresponding ester or thioester as products: 0 II
R-Cg-X-R'
+ H,O + RCH,C-X-R'
X=OorS
These data were interpreted to indicate the mechanism in Scheme I. The general acid catalysis, the deuterium solvent isotope effects, and the lack of deuterium incorporation upon partial hydration in D20 are particularly convincing evidence for a rate-determining protonation and the discrete intermediacy of a vinyl cation such as 6 . As the alkyl groups R are varied on compounds 2-5, the rates of hydration
PETER J. STANG
208
RCS-X-R'
+ H,O'
H \
%
x=o.s
e
R
\
/ R H \
e
C=C-X-R' + H,O
\
fast
--+
@OH, I
/C=C-x-R' R @OH, I C=C-X-R'
/
H
YH CS-X-R'
/ R
\
+ H,O +
R
H,
+ H,O
6
H
H
X-R'
/"="
OH I
C=C-X-R' + H 3 0 e
/
R 0 II
== RCH,C-X-R'
Scheme I. Mechanism of Hydration of Alkynyl Ethers and Thioethers.
follow the Taft relation (1 l), with p* = -6.6 for 2 (4, 7), p * = -2.57 for 3 (13), = -.73 for 4 (9), and p* = -3.76 for 5 (9). The large negative rho values are in accord with the proposed electrophilic attack by a proton in the ratedetermining step. The magnitude of the rho value in 2 relative to that in 4 suggests that oxygen is a much better transmitter of polar effects than is sulfur. In the hydration of compounds 2f and 2g, besides the expected ester, three other products (acetic acid, an alkene, and alcohol) were observed. These products were postulated to arise via a fragmentation of the intermediate vinyl cation, 6, as shown in Scheme 11. The importance of the fragmentation path is presumably determined by the stability of the alkyl cation formed by the alkyl oxygen fission. Product studies, general acid catalysis, and kinetic data indicate that hydration of compounds I and 8 also proceed by way of a vinyl cation (12, 13). p*
R
Et-X-CEC-C-
I I
R
7,X=S a,R=Me 8 , X = 0 b, R = Et
OH
However, the rates of hydration of these compounds are about a factor of ten to one hundred faster than predicted by means of the Taft relation. Anchimeric assistance by the hydroxyl group in the transition state for protonation, 9, has
VINYL AND ALLENYL CATIONS
209
CH, CH3 CH3 I H” @ I Q I H C g - 0 - C - R ---t H,C=C-0-C-R * H,C=C=O-C-R I VI CH3
1
R = H, CH, cH3/
7H3 H2C=C-O-C-R I I @OH, CH,
I1
hH36
\H,O
0II 7H3 CH,C-0-C-R I CH3
YH3
+
HzC=C=O
R-CQ I
O..\“../
0 II CH,C-OH
yI3
( 7 3
R-C
II
CHZ
R-C-OH I CH3
Scheme 11. Mechanism of Hydration of 2f and 2g.
been suggested as an explanation of this discrepancy (12, 13).
Clearly, a large body of diverse evidence indicates that the acid-catalyzed hydration of alkynyl ethers and thioethers proceeds via a rate-determining protonation through a vinyl cation. However, these vinyl cations are unique in that they have a resonance form where the positive charge resides on the el
R-X-C=CHR’
B
+---*
R-X=C=CHR’
heteroatom via delocalization of the lone electron pairs on either oxygen or sulfur. The result is special stability in such ions. The situation is analogous to the behavior of ordinary carbonium ions generated by solvolysis, where a-halo ethers are some lo6 more reactive than unsubstituted halides (14). The importance of such resonance contributions involving the heteroatom also accounts for the lo3 to lo4 times greater reactivity of the alkynyl ethers compared to the analogous thioethers. Since overlap of the empty p orbital on the vinyl carbon must be much better with the lone-pair electrons in the 2p orbitals of oxygen than with the lone-pair electrons in the more diffuse 3p orbitals of sulfur.
210
PETER J. STANG
2. Electrophilic Additions to A rylacetylenes
Although the reaction of certain acetylenes such as phenylacetylene and ethyl phenylpropiolate with cold concentrated sulfuric acid to give acetophenone (1 5 ) and benzoylacetic acid (1 6) has been known since the 1880's, it was only in the 1960's that this reaction was studied mechanistically. The relative rates of hydration of arylacetylenes in acetic acid: water: sulfuric acid to the corresponding acetophenones were investigated by Bott et al. (17), and they are listed in Table I. TABLE I Hydration of Substituted Phenylacetylenes in Acetic Acid : Water : Sulfuric Acid at 50.2"C(17) Substituent mCF, m-Br m €I p-Br P-I PC1
m-Me0 H mCH, p-2-B~ P-W P-CH 3 0
ki
krel
.0047 ,018 .021 .22 .24 .28 .52
1 .oo 1.92 10.5 15.6 950.0
As the data in Table I indicate, there is a strong dependence of the hydration on the electron demands of the substituents, with a rho of -4.3 in the Yukawa-Tsuno (18) equation, where log k is plotted against p [a + r ( d - a)]. Partial hydration of C6 H5CE CT and recovery of the unreacted starting material did not result in any loss of specific activity, which indicates that the protonation of the triple bond is not significantly reversible and hence is rate determining. A more detailed study of the hydration of phenylacetylene, 9a, and three substituted phenylacetylenes, p-methoxy 10, p-methyl 1 1, and p-chlorophenylacetylene 12, in aqueous sulfuric acid containing 5% ethanol has been carried out by Noyce and co-workers (19,20). The hydration obeys general acid catalysis and gives a linear Ho dependence. The slopes for the logarithm of the observed rate constants versus Ho and the activation parameters for the hydration of these phenylacetylenes are summarized in Table 11.
VINYL AND ALLENYL CATIONS
211
TABLE I1 Acidity Dependence and Activation Parameters for Hydration of Phen ylacet y lenesa Compound 9a
10 11 12
T,"C
24.92 44.11 24.88 44.93 24.88 44.93 24.86 44.63
- _log _ dH0 1.24 f .01 1.189 f .006 1.185 f .015 1.005 f .008 1.26 i .03 1.149 f .001 1.17 f .01 1.195 i .006
AHS(kcal/mole)
ASS(e.u.)
20.9
-18.2
15.7
-21.6
21.6
-10.4
16.7
-33.6
a Data from (20).
Noyce and Schiavelli (21) also measured the rate of hydration of the above phenylacetylenes in deuteriosulfuric acid solution. Values of the observed solvent isotope effects, kH,O/kD,O, are summarized in Table 111. TABLE I11 Solvent Deuterium Isotope Effects for the Hydration of Phenylacetylenes at 250a Compound 9a
10 11 12
-H, range
2.34-3.24 -.73-.60 .85-2.12 1.91-3.21
(kH,sO,/kD
(kH, s o , / k ~ so,)' ,
2.67-3.32 2.67-3.1 8 2.39-2.74 2.97-3.10
2.46 3.82 2.70 2.98
a Data from ref. (21).
Range of values observed over the acidity range. Isotope effect at Ho = -2.0.
The experiments of Bott (1 7) and Noyce (19-2 1) show that a vinyl cation best represents the intermediate in the hydration of phenylacetylenes. In particular, the large solvent isotope effects observed indicate a rate-limiting protonation and formation of a vinyl cation, for these values are not in agreement with solvent isotope effects observed for compounds which react by other possible mechanisms, such as one involving equilibrium formation of the vinyl cation followed by the slow attack by water.
212
PETER J. STANG
*
From a knowledge that the equilibrium C6H5CzCHt H 2 0 C6HSCOCH3 lies 37 kcal/mole in favor of the ketone (22) and of the data of Ziicher and Hammett (23) on the rate of enolization of acetophenone, combined with an estimate of the enol content of acetophenone (.00190) (24), Noyce and Schiavelli (20) have summarized the above data in an elegant energy-reaction coordinate diagram, shown in Figure 1.
Reaction coordinate
Figure 1. Energy-reaction coordinate diagram for the acid-catalyzed hydration of phenylacetylene. The ordinate is not to scale (20).
Rate-determining protonation to give a vinyl cation rather than 1,4 addition of water has been proposed as the most consistent mechanism (25) for the acid-catalyzed hydration of arylpropiolic acids in aqueous sulfuric acid. Hydration of arylpropiolic acid closely resembles the acid-catalyzed isomeriza-
ArC=GCO,H
0 11 Arc=(-C-OH
H'
ArC=CHCO,H HZ
H+
6H 11 Arc=(-C-OH
H O
OH I ArC=CHCO,H
-+
Products
+
Products
+OH, OH I
I
1 ArC=C=C-OH
VINYL AND ALLENYL CATIONS
21 3
tion of cis-cinnamic acids, which has been demonstrated to occur by a rate-determining protonation of the double bond (26):
The rates of hydration of substituted phenylpropiolic acids give a rho of -4.77 when plotted against u’ , comparable to ’the acid-catalyzed isomerization of cis-cinnamic acid, with a rho value of -4.3. The solvent deuterium isotope effects are kH2S04/kD2S0, = 3.7-5.2 for the isomerization of cinnamic acids at 45°C and 2.4 - 5.3 for the hydration of arylpropiolic acids at 25°C in 50% sulfuric acid. The rates of both reactions give a linear correlation when plotted against Ho , with a slope of near unity; and both reactions have comparable high negative entropies of activation. In contrast, the acid-catalyzed hydration of arylbenzoylacetylenes differs markedly from the hydration of a,P-unsaturated ketones. Hydration of unsaturated ketones has been shown to proceed via a 1,Caddition mechanism where protonation occurs on oxygen to give an oxonium salt, followed by attack of water at the 0-carbon to give a hydroxy enol. The rate-limiting step has been shown to be the protonation of the hydroxy enol(27): 0 eOH OH OH 11 H+ II I I RCH=CHC-R # RCH=CHCR 4 RCHCH=C-R OH OH I I RCHCH=C-R + H
slow
0 @OH OH I1 I II RCHCH2CR + RCHCH, CR OH I
In contrast, the hydration of arylbenzoylacetylenes is believed to proceed via a vinyl cation formed by rate-determining protonation on carbon (28): 0 II XC, H,C*-C-C,
H,
+H
-
e slow
0 I1 XC, &C=CHCC, H, @
--+ --+
0 0 II II XC6H4CCH2CC6H5
The evidence presented includes the observed solvent isotope effect of the high negative rho of -4.21, and the high negative entropies of activation (-27 e.u. to -35 e.u.). The negative entropy of activation is in line with values observed for other rate-limiting transfers to unsaturated carbons (29). Vinyl cations also have been invoked as intermediates in the electrophilic addition of HCl to 1-phenylpropyne in acetic acid. Fahey and Lee (30,3 1) have shown that the reaction is first order in 1-phenylpropyne and between first and second order in HC1. The observed products were cis-(-75%) and truns-(-lO%) 1-chloro-1-phenylpropene,along with about 15% propiophenone. Control experiments demonstrated that the propiophenone arose from cis- and trans1-acetoxy-1-phenylpropene. The results were best explained by rate-determining kH2S04/kD2S0,=2.2-3.9,
214
PETER J. STANG
protonation and formation of vinyl-cation ion pairs rather than by a concerted cyclic addition, which would have required the formation of all cis products. Recent studies by Pincock and Yates (32, 33) have demonstrated the intermediacy of vinyl cations in the electrophilic bromination of arylmethylacetylenes in acetic acid. The rates of addition of Br2 to a number of substituted phenylmethylacetylenes in acetic acid follow the general equation
where [AMA] is the concentration of arylmethylacetylene; [Brz ] the bromine concentration; and k2,k3 and kBr- are specific rate constants. The term in kBronly applies in the presence of added bromide ion. A rho value of - 5.2 was observed for a plot of log kz vs. u* in this reaction. This value is comparable to those observed in the acid-catalyzed hydrations of various arylacetylenes (20,25,28) as well as to the rho value of -4.5 observed in the bromination of styrenes in acetic acid (34,35). In accord with previous observations in rate-limiting electrophilic additions, the entropies of activation are highly negative, with values around -30 e.u. The products of addition consist of about 70% trans- and 13% cis-l,2-dibromoolefins, C6H5CBr=CCH3(Br), along with 27% of solvent-incorporated products. The solvent-incorporated products are regiospecific in the Markovnikov sense, consisting of cis- and trans-l-acetoxy1-phenyl-2-bromopropeneand 0 II C, H,CCBr,R.
The dibromoketone is formed from the bromoacetates in a secondary reaction. These results have been accounted for by the authors via an ion-pair scheme shown in Figure 2. In contrast to the above behavior, in the presence of .1 M LiBr phenylacetylene yields the trans dibromide, C6HSCBr=CHBr, in greater than 99% yield upon the addition of Brz in acetic acid (35). This difference in behavior between the two systems has been accounted for by the formation of a different intermediate ion, 13, in the latter case.
13
Cleavage of arylethynyltriethylgermanes by perchloric acid in aqueous methanol has been proposed to proceed via a vinyl cation (36). A rho value of -3.3 was
cHap;)H * Ar&CHGe(Et),
ArC-=CGe(Et), +H+
+
ArMH
215
VINYL AND ALLENYL CATIONS Ph-CEC-R
+
/
Br,,C=C,
Br2
Ph
Br R
Ph,
,c=c, /
AcO
R
\
HOAc ‘R
-
l HOAC Ph--d=C: Br-
Br
HOAc + ,Br Ph-CaC,
I
HOAc
Br
/
R
Figure 2. General ion-pair scheme for the addition of bromine to phenylacetylene in acetic acid (33).
observed for this reaction in the Yukawa-Tsuno relation. Vinyl cations may also be involved as intermediates in the formation of lactones in sulfuric acid from diarylacetylenes with ortho carboxyl groups (37). However, this reaction may also proceed by a concerted process, and it is difficult to establish the exact reaction mechanism. Once again, a large amount of diverse evidence indicates the intermediacy of a vinyl cation in electrophilic additions to arylacetylenes. As in the case of the hydration of alkynyl ethers and thioethers, the vinyl cation formed is especially stable because of resonance interaction and charge delocalization with the adjacent center of the aromatic system.
3. Electrophilic Additions to Alkylacetylenes and Acetylene Peterson and co-workers have carried out a careful investigation of the electrophilic addition of trifluoroacetic acid to a series of aliphatic alkynes (38) and alkenes (39,40). Of particular interest is the behavior of 3-hexyne. At .1 M concentrations of 3-hexyne, nearly equal amounts of the cis- and trans3-hexen-3-yl trifluoroacetates are formed in 98% yield, together with about 2% 0 II OC-CF3 I
CH, CH, C=CHCH, CH,
of hexaethylbenzene. At a concentration of 1.4 M, the hexaethylbenzene yield
PETER J. STANG
216
increases to 24%. The nonstereospecific addition is consistent with formation of a vinyl cation which can collapse with solvent to give the observed cis and trans trifluoroacetates or react further with unreacted alkyne in solution to form the hexaethylbenzene. The latter product presumably arises via dimeric intermediates, although no dimers as such were isolated. Further evidence for rate-determining protonation and vinyl cations comes from the close similarity of substitutent effects and general behavior for additions of trifluoroacetic acid to alkynes (38) and alkenes (40). Extensive investigations have clearly established protonation as the rate-determining step for electrophilic addition of trifluoroacetic acid to alkenes (40). Addition of trifluoroacetic acid to 5-substituted-1-alkynes of the type (X = I, Br, CI, F, CH,O, OAc, etc.)
X
yields rearranged products presumably through 5-membered cyclic intermediates (41). Formation of such cyclic intermediates could involve vinyl cations, or they could arise via a concerted process. The available evidence would indicate a concerted process rather than discrete vinyl cations.
In contrast to the behavior of 3-hexyne in trifluoroacetic acid, addition of HC1 in acetic acid yields essentially trans-3-chloro-3-hexene (48%) and 3-hexanone (52%) as products, with less than 1% of the cis chloride (3 1,42,43). The 3-hexanone has been shown to arise from an intermediate vinyl acetate. The kinetics are complicated, but they seem to be of first order in substrate and second order in HC1. Added tetramethylammonium chloride increases the rate of product formation and changes the product composition to >95% trans3-chloro-3-hexene and <5% 3-hexanone. A termolecular electrophilic addition via an intermediate such as 14 has been proposed (31,42) to account for these data. A-
14
X = H ; Y = OAcor C1 X = (CH,), N;Y = CI
VINYL AND ALLENYL CATIONS
217
Yet another intermediate, a cyclic bromonium ion, 15, is involved in the electrophilic addition of bromine to 3hexyne, 1-hexyne (32,33), and other alkylacetylenes (44). In these reactions, only trans dibromides have been
-c-=c. , /
s'
Br 0
15
observed as products, formed via bimolecular kinetics (32). Similar cyclic intermediates, 16, have been invoked in the addition of sulfenyl halides to alkynes (45) and aIkenes (46).
--c=c*;&J
S I
R 16
The exact behavior and mechanism of electrophilic additions to alkynes is clearly strongly dependent upon the reaction conditions. In a highly polar and strongly acidic but weakly nucleophilic solvent such as trifluoroacetic acid, addition via a vinyl cation intermediate is favored; whereas in less polar, more nucleophilic solvents such as acetic acid, a different mechanism prevails. The addition of hydrogen halides to methylacetylene also has been investigated (47,48). When the additions were carried out neat in a 1 : 1 ratio at -7O"C, besides two acyclic products, CH3CX=CH2 and CH3CX2CH3,substantial amounts of two cyclic products, cis- and truns-l,3-dihalo-l, 3-dimethylcyclobutane were observed along with some minor products (48). Similar results were observed in the addition to allene (vide infra). Although no substantial experimental evidence other than the observed products was offered, the results were accounted for by a vinyl cation hypothesis (48). Protonation yields the intermediate vinyl cation 17, which could collapse to give product 18 or react with excess propyne to give the observed cyclic products.
CH,CH=CH
+ HX
[CH,C=CH, J
l7
X I
b
CH,--C-CH,
I
-
CH,CX=CH,
b
I
H, C-C-CH, I X
1. ~e
CH,-C-CH,
t -
*. HX
I
I
HCsC-CH,
7
18
kCrCH CH,-C=CH,
IC.
H-C=C-CH, b
In contrast to the work of Peterson (38) with 3-hexyne in trifluoroacetic acid (vide supra), n o trimeric adducts were observed in the hydrogen halide additions to propyne (48).
PETER J. STANC
218
Vinyl cations also have been invoked as intermediates in the reaction of HCl with t-butylacetylene (49). With neat mixtures in the liquid phase at ambient temperatures, the following four products were observed: CI t-Bu-C=CH,,
(CH,),CCI,CH,,
(CH,),CClCCI(CH,),,
CH, C1 I I CICH,CH C(CH,),
19
20
21
22
I
Products 19 and 20 result from the collapse of vinyl cation 23 with CI- to give 19, and the subsequent reaction of this product with HCl gives 20. Compounds 2 1 and 22 could arise from either a 1,2-methyl shift to vinyl cation 23 or CH, CH3 I I m CH,-CXkCH+HCl+CH,-C-C=CH, I I CH, CH, 23
via neopentyl-type rearrangements. Thus, 21 could be formed by a methyl migration during the addition of HCl to 19 and 22 by a series of two anti-Markovnikov additions to t-butylacetylene and a concurrent methyl
c1
CH, I m f-Bu-C=CH, +CH,-C- C-CH, I I CH, C1
H+
I
C1 m
I
(CH,),C-C(CH,),
Cl* __+
21
19
migration during the second addition step (49). However, reaction of an H+
HCI
(CH,),C-C*H
(CH,),CCH=CHCI
+
24
-f
CH, CH, I I (CH,),CCHCH,Cl+ gC- CH-CH,CI m
I
CH3 J.
c1-
22
authentic sample of 19 with HCl produced no 21, but only 20, and the formation of 22 from authentic 24 and HCl is too slow under the reaction conditions employed to account for its formation via this route. Hence, 21 and 22 arise via a 1,2-methyl shift to vinyl cation 23 and the subsequent reaction of the resultant rearranged allylic ion. (For a detailed discussion of rearrangements in vinyl cations, see section IV.F.l.) Vinyl cations also have been invoked as intermediates in the addition of carbonium ions generated in strong acid to acetylene (50-53). Sasaki et ai. (SO) observed 1-adamantyl methyl ketone, 25, as the sole product in the reaction of acetylene with 1-bromoadamantane in concentrated Hz SO4 at 5". Bott (5 1 ), on the other hand, reported a mixture consisting of 75% 1-adamantylacetaldehyde,
VINYL AND ALLENYL CATIONS
219
26, and 25% methylhomoadamantanone, 27, in the reaction of l-hydroxyadamantane with acetylene in 90-95% H2SO4 at 4-7'C. Presumably the first
26
25
27
step in each of these reactions is the formation of the stable adamantyl carbonium ion, which then adds to acetylene to give a vinyl cation intermediate 28.
X = OH, Br
28
The subsequent fate of this intermediate primary vinyl cation 28 seems to be in doubt and dependent upon the exact reaction conditjons. In concentrated (98%) Hz SO4, ion 28 seems to undergo a rapid hydride migration to form the more stable vinyl cation 29, which in turn is trapped by water to give ketone 25
G
c
H
28
E
H
-
%
&-z-CH2
25
29
as the major or sole product (50); whereas in 90-95% sulfuric acid, ion 28 is mostly trapped to give 26 as the major product, with only 25% rearranged product 27 ( 5 1). Product 27 was proposed to arise as follows (5 1):
21
However, more recent evidence (53) indicates that sulfates may be involved as intermediates and the rearranged product 27 arises via a synchronous process rather than through ion 29. Direct protonation of adamantylacetylene in 90%
2 20
PETER J. STANG
