ADVANCED
`ORGANIC
`CHEMISTRY
`
`REACTIONS,
`MECHANISMS, AND
`STRUCTURE
`
`THIRD EDITION
`
`Jerry March
`Professor of Chemistry
`Adelphi University
`
`A Wiley-Interscience Publication
`
`JOHN WILEY & SONS
`
`New York • Chichester • Brisbane • Toronto • Singapore
`
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`

`
`Copyright © 1985 by John Wiley & Sons, Inc.
`
`All rights reserved. Published simultaneously in Canada.
`
`Reproduction or translation of any part of this work
`beyond that permitted by Section 107 or 108 of the
`1976 United States Copyright Act without the permission
`of the copyright owner is unlawful. Requests for
`permission or further information should be addressed to
`the Permissions Department, John Wiley & Sons, Inc.
`
`Library of Congress Cataloging in Publication Data:
`March, Jerry, 1929-
`Advanced organic chemistry.
`
`"A Wiley-Interscience publication."
`Includes bibliographical references and indexes.
`l. Chemistry, Organic.
`I. Title.
`
`QD251.2.M37 1985
`ISBN 0-471-88841-9
`
`547
`
`84-15311
`
`Printed in the United States of America
`
`10 9 8 7 6 5 4
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`16
`
`LOCALIZED CHEMICAL BONDING
`
`Inductive and Field Effects
`
`The C-C bond in ethane is completely nonpolar because it connects two equivalent atoms.
`However, the C -C bond in chloroethane is polarized by the presence of the electronegative chlorine
`atom. This polarization is actually the sum of two effects. In the first of these, the C-1 atom,
`having been deprived of some of its electron density by the greater electronegativity of Cl, is
`&+
`8-
`H3C---+-CHz ~cl
`
`2
`
`partially compensated by drawing the C-C electrons closer to itself, resulting in a polarization
`of this bond and a slightly positive charge on the C-2 atom. This polarization of one bond caused
`by the polarization of an adjacent bond is called the inductive effect. The effect is greatest for
`adjacent bonds but may also be felt farther away; thus the polarization of the C-C bond causes
`a (slight) polarization of the three methyl C-H bonds. The other effect operates not through
`bonds, but directly through space or solvent molecules, and is called the field effect. 31 It is often
`very difficult to separate the two kinds of effect, but it has been done in a number of cases, generally
`by taking advantage of the fact that the field effect depends on the geometry of the molecule but
`the inductive effect depends only on the nature of the bonds. For exam_ple, in isomers l and 232
`the inductive effect of the chlorine atoms on the position of the electrons in the COOH group (and
`
`COOH
`
`COOH
`
`pK. = 6.07
`1
`
`pK. = 5.67
`
`2
`
`hence on the acidity, see Chapter 8) should be the same since the same bonds intervene; but the
`field effect is different because the chlorines are closer in space to the COOH in l than they are
`in 2. Thus a comparison of the acidity of l and 2 should reveal whether a field effect is truly
`operating. The evidence obtained from such experiments is overwhelming that field effects are
`much more important than inductive effects. 33 In most cases the two types of effect are considered
`together; in this book we will not attempt to separate them but will use the name field effect to
`refer to their combined action.
`Functional groups can be classified as electron-withdrawing (-I) or electron-donating ( + /)
`
`31Roberts and Moreland, J. Am. Chern. Soc. 75, 2167 (1953).
`32This example is from Grubbs, Fitzgerald, Phillips, and Petty, Tetrahedron 21, 935 (1971).
`33For example, see Dewar and Grisdale, J. Am. Chern. Soc. 84, 3548 (1962); Stock, J. Chern. Educ. 49, 400 (1972);
`Golden and Stock, J. Am. Chern. Soc. 94, 3080 (1972); Cole, Mayers, and Stock, J. Am. Chern. Soc. 96, 4555 (1974); Modro
`and Ridd, J. Chern. Soc. 8 528 (1968); Liotta, Fisher. Greene, and Joyner, J. Am. Chem. Soc. 94, 4891 (1972); Wilcox and
`Leung, J. Am. Chern. Soc. 90, 336 (1968); Butler, J. Chern. Soc. 8 867 ( 1970); Adcock, Bettess, and Rizvi, AtW. J. Chem.
`23, 1921 (1970); Rees, Ridd, and Ricci, J. Chern. Soc., Perkin Trans. 2, 294 (1976); Topsom, Prog. Phys. Org. Chem. 12,
`1-20 (1976); J. Am. Chern. Soc. 103, 39 (1981 ); Grob, Kaiser, and Schweizer, Hetv. Chirn. Acta 60, 391 ( 1977); Reynolds,
`J. Chern. Soc., Perkin Trans. 2, 985 (1980), Prog. Phys. Org. Chern. 14, 165-203 (1983); Bowden and Hojatti, J. Chern
`Soc., Chern. Cornmun. 273 (1982). For another view, see Exner and Fiedler. Cotlect. Czech. Chern. Cornmun. 45, 1251 (1980).
`
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`
`CHAPTER I
`
`LOCALIZED CHEMICAL BONDING
`
`17
`
`groups relative to hydrogen. This means, for example, that N0 2 , a -I group, will draw electrons
`to itself more than a hydrogen atom would if it occupied the same position in the molecule.
`
`0 2N-+-+-CH2-Ph
`H--CH2--Ph
`
`Thus, in 0'-nitrotoluene, the electrons in the N-C bond are farther away from the carbon atom
`than the electrons in the H-C bond of toluene. Similarly, the electrons of the C-Ph bond are
`farther away from the ring in 0'-nitrotoluene than they are in toluene. Field effects are always
`comparison effects. We compare the -I or +I effect of one group with another (usually hydrogen).
`It is commonly said that, compared with hydrogen, the N02 group is electron-withdrawing and the
`0- group electron-donating or electron-releasing. However, there is no actual donation or with(cid:173)
`drawal of electrons, though these terms are convenient to use; there is merely a difference in the
`position of electrons due to the difference in electronegativity between H and N02 or between H
`and o-.
`Table 3 lists a number of the most common -I and +I groups. 34 It can be seen that compared
`with hydrogen, most groups are electron-withdrawing. The only electron-donating groups are groups
`with a formal negative charge (but not even all these), atoms of low electronegativity, such as Si,
`Mg, etc., and perhaps alkyl groups. Alkyl groups35 have usually been regarded as electron-donating,
`but in recent years many examples of behavior have been found that can be interpreted only by
`the conclusion that alkyl groups are electron-withdrawing compared with hydrogen. 36 In accord
`with this is the value of 2.472 for the group electronegativity of CH 3 (Table 2) compared with
`2.176 for H. We shall see that when an alkyl group is attached to an unsaturated or trivalent carbon
`(or other atom), its behavior is best explained by assuming it is +I (see, for example, pp. 143,
`152, 234, 457), but when it is connected to a saturated atom, the results are not as clear and alkyl
`groups seem to be +I in some cases and -/ in others37 (see also p. 235). Similarly, it is clear
`
`TABLE 3 Field effects of various groups relative
`to hydrogen
`
`The groups are listed approximately
`in order of decreasing strength for both -I and
`+I groups
`
`+I
`
`o-
`coo-
`CR 3
`CHR2
`CH 2R
`CH 3
`D
`
`-I
`
`COOH
`F
`Cl
`Br
`I
`OAr
`COOR
`
`NR 3 +
`SR 2 +
`NH 3 +
`N02
`S02R
`CN
`S0 2 Ar
`
`OR
`COR
`SH
`SR
`OH
`C=CR
`Ar
`CH=CR 2
`
`34See also Ceppi, Eckhardt, and Grob, Tetrahedron Lett. 3627 (1973).
`35For a review of the field effects of alkyl groups, see Levitt and Widing, Prog. Phys. Org. Chern. 12,-119-157 (1976).
`36See Sebastian, J. Chern. Educ. 48, 97 (1971).
`37See, for example, Schleyer and Woodworth, J. Am. Chern. Soc. 90, 6528 (1968); Wahl and Peterson, J. Am. Chern.
`Soc. 92, 7238 (1970). The situation may be even more complicated. See, for example, Minot, Eisenstein, Hiberty, and Anh,
`Bull. Soc. Chim. Fr. Il-119 (1980).
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`18
`
`LOCALIZED CHEMICAL BONDING
`
`that the field-effect order of alkyl groups attached to unsaturated systems is tertiary > second(cid:173)
`ary > primary > CH3 , but this order is not always maintained when the groups are attached to
`saturated systems. Deuterium is electron-donating with respect to hydrogen. 38 Other things being
`equal, atoms with sp bonding generally have a greater electron-withdrawing power than those with
`.rp 2 bonding, which in tum have more electron-withdrawing power than those with sp 3 bonding. 39
`This accounts for the fact that aryl, vinyl, and ethynyl groups are -/. Field effects always decrease
`with increasing distance, and in most cases (except when a very powerful +I or -/ group is
`involved), cause very little difference in a bond four bonds away_ or more.
`For discussions of field effects on acid and base strength and on reactivity, see Chapters 8 and
`9, respectively.
`
`Bond Distances40
`
`The distances between atoms in a molecule are characteristic properties of the molecule and can
`give us information if we compare the same bond in different molecules. The chief methods of
`determining bond distances and angles are x-ray diffraction (only for solids), electron diffraction
`(only for gases), and spectroscopic methods. The distance between the atoms of a bond is not
`constant, since the molecule is always vibrating; the measurements obtained are therefore average
`values, so that different methods give different results. 41 However, this must be taken into account
`only when fine distinctions are made.
`Measurements vary in accuracy, but indications are that similar bonds have fairly constant
`lengths from one molecule to the next. The variation is generally less than I%. Thus for a bond
`between two sp3 carbons the following results have been found:
`
`C-C bond in
`
`Diamond
`CzH,
`C2H5CI
`C3Hs
`
`Bond length, A
`1.54442
`1.5324 ± 0.001143
`1.5495 ± 0.000544
`1.532 ± 0.00345
`
`c-c bond in
`Cyclohexane
`t-Butyl chloride
`n-Butane to n-heptane
`Isobutane
`
`Bond length, A
`1.540 ± 0.01546
`1.53247
`1.531-1.53448
`1.535 ± 0.001 49
`
`Bond distances for some important bond types are given in Table 4. As can be seen in this
`table, carbon bonds are shortened by increasing s character. This is most often explained by the
`
`38Streitwieser and Klein, J. Am. Chem. Soc. 85, 2759 (1963).
`39Bent, Chem. Rev. 61, 275-311 (1961), p. 281.
`40For a review of this subject and of bond angles, see Ref. 39. For tables of bond distances and angles, see Tables of
`Interatomic Distances and Configurations in Molecules and Ions, Chem. Soc. Spec. Pub/. No. II (1958); Interatomic Distances
`Supplement, Chern. Soc. Spec. Pub/. No. 18 (1965); Harmony, Laurie, Kuczkowski, Schwendeman, Ramsay, Lovas, Lafferty,
`and Maki, J. Phys. Chem. Ref. Data 8, 619-721 (1979); Rogowski, Fortschr. Chem. Forsch. 4, 1-50 (1963), pp. 22-31.
`For a review of molecular shapes and energies for many small organic molecules, radicals, and cations calculated by molecular(cid:173)
`orbital methods, see Lathan, Curtiss, Hehre, Lisle, and Pople, Prog. Phys. Org. Chem. 11, 175-261 (1974).
`41Whiffen, Chem. Br. 1, 57-61 (1971); Stals, Rev. Pure App/. Chem. 20, 1-22 (1970), pp. 2-5; Lide, Tetrahedron 17,
`125 (1962).
`42Lonsdale, Phil. Trans. R. Soc. London A240, 219 (1947).
`43Bartell and Higginbotham, J. Chem. Phys. 42, 851 (1965).
`44Wagner and Dailey, J. Chem. Phys. 26, 1588 (1957).
`451ijima, Bull. Chem. Soc. Jpn. 45, 1291 (1972).
`46Tables of Interaton .. ~ Distances, Ref. 40.
`47Momany, Bonham, and Druelinger, J. Am. Chem. Soc. 85, 3075 (1963); also see Lide and Jen, J. Chem. Phys. 38,
`1504 (1963).
`48Bonham, Bartell, and Kohl, J. Am. Chem. Soc. 81, 4765 (1959).
`49Hilderbrandt and Wieser, J. Mol. Struct. 15, 27 (1973).
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