Substituent Effects in Organic Polarography

Substituent Effects in Organic Polarography

Petr Zuman Heyrovsky Institute of Polarography Czechoslovak Academy of Sciences Prague, Czechoslovakia

With a Foreword by

J. Heyrovsky

<±' PLENUM PRESS· NEW YORK· 1967

ISBN 978-1-4684-8663-6 ISBN 978-1-4684-8661-2 (eBook) DOT 10.1007/978-1-4684-8661-2

Library of Congress Catalog Card Number 63-17643

© 1967 Plenum Press Softcover reprint of the hardcover 1st edition 1967

A Division of Plenum Publishing Corporation 227 West 17 Street,New York, N. Y.10011

All rights reserved

No part of this publication may be reproduced in any form without written permission from the publisher

To the memory of Professor J. Heyrovsk'y, my esteemed teacher

Foreword

During the forty years which have passed since Masuzo Shikata published his paper on the reduction of nitrobenzene at a dropping mercury electrode, the number of polarographic studies of organic compounds in the literature has risen to several thousands. The ever­increasing amount of experimental data was in need of some unified method of classification which would yield unambiguous and possibly complete information on the polarographic behavior of organic substances.

Dr. Zuman's book presents an original attempt to meet this need by providing a system based on correlations between the polaro­graphic half-wave potentials of organic depolarizers and their Hammett constants. I consider this a very happy conception, for, more than any other book yet written, it brings polarography nearer to the organic chemist; and it will undoubtedly convince him that, in its application to his subject, the method is more than a mere analytical tool.

The author hardly needs any introduction. During many years of research in the field of organic polarography, he has published numerous papers on a variety of problems; his latest interest is the application of the Hammett-Taft equation to polarographic measure­ments, in which he has done pioneering work.

It remains for me to hope that this book, which opens up new prospects for the fruitful application of polarography, may inspire

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some reader with useful ideas in his search for new paths in his research problems.

Prague November, 1966

J. HEYROVSKY

1890-1967

Preface

"Habent sua fata libelli"

Though the above quotation usually is made about books which have already been published, the fates of manuscripts which have not yet appeared in print may sometimes be even more devious and uncer­tain. Even among scientific books, there are some for which the road between the first draft and the final text is short and smooth, but for many it is unfortunately long and tedious. These are the cases in which the "finish" in Michael Faraday's "Work, finish, publish!" is definitely the most difficult of the three, and it is to this category that the present manuscript belongs.

Its story started as early as 1955, when Plenum Press asked me for permission to prepare and publish an English translation of my review article entitled "Effects of Constitution on the Polarographic Behavior of Organic Substances," which appeared in Czech in Chemicky Listy in 1954. I agreed, but at the same time I made a decision which-young authors note and be warned !-was much easier to make than to implement, namely, to rewrite the article and bring it up to date. As the years passed, this project merged with one associated with my research interests, and it culminated in a D.Sc. thesis entitled "General Equation for Substituent Effects on Half-Wave Potentials of Organic Substances." The collection of material for the projected book was complete in 1959, but the matter was not in the form of a final

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manuscript, and also the question of a translator remained open. In the meantime I tried to improve my English, and during a short but pleasant visit to the New York offices of Plenum Press (where it was realized with some surprise that I am indeed a human being, and not just a ghost appearing only in the correspondence) it was agreed that I, myself, should prepare an English manuscript. However, during the rewriting of the text, which started in 1963, I found that the appearance of new material since 1959 made it necessary to make a very extensive revision of most of the chapters. These changes were sometimes so substantial that, for example, the last chapter (Alicyclic Compounds), which was some 12 pages long in the 1959 version, grew to about 60 in 1965. May I, again, interpose a word to younger authors based on my experience with two other monographs? It is much more pleasant and interesting to make a new dress than to remake an old one! Because this revision was time-consuming, the coverage of the literature varies; whereas, the polarographic literature was considered up to at least 1963 in the first chapters and up to 1965 in the last ones, the treat­ment of the theory of linear free energy relations corresponds to its state in 1961-62. The important contributions published in the 1963-65 period could not be considered because of the technical problems involved.

I was extremely pleased when a reviewer described one of my books as "readable," but I am afraid that no such epithet can be applied to the present monograph. This book has two principal aims. The first is to show organic polarographers the types of structural problems which can be treated quantitatively, to stress the experimental conditions which must be observed for such treatments to be valid, and, above all, to show what kinds of experiments it would be important to carry out in the future and what criteria should be used in selecting organic compounds for polarographic studies. Furthermore, the present treatment reveals the possibility of generalizing interpretations of the effects of substituents on polarographic behavior, and it presents an advantageous organization of experimental data. From the elec­trochemical point of view, the present treatment is important in reveal­ing the fundamental fact that electrode processes, which are essentially heterogeneous, are, in principle, affected by structure in the same way as homogeneous reactions.

The second aim is to show physical organic chemists the possi­bilities that polarography offers for the solution of fundamental, and also applied, problems in their field. The greatest obstacle, in this

Preface xi

respect, is the limited number of compounds in most of the reaction series for which half-wave potentials have been measured so far.

My thanks must be expressed to Drs. O. Exner and V. Hanus, who read the whole of the Czech manuscript, and to Dr. M. Charton (chapter on Quinones), and Drs. W. Klyne and V. Delaroff (chapter on Alicyclic Compounds), who read the manuscripts of some of the chapters in an uncomplete form.

My special thanks are due to Dr. A. E. Stubbs, who not only polished by English and style with a subtle feeling for my ideas and the subject matter, but also unified the scientific terminology and organic nomenclature and drew my attention to several inconsistencies. When I consider my own timetable, I am put to shame by the speed with which this thorough and careful revision work was done.

Last, but definitely not least, my thanks are directed to the pub­lisher and all his associates for their kind patience and understanding. One of the editors recently wrote "I look forward to the publication with considerable satisfaction; that a project of so many years' standing has finally become reality affirms one's belief that not all human plan­ning is in vain," and this best expresses their kind and courteous attitude to all the troubles which they have had with me and my manu­script. I thank them.

Prague October, 1966

P. ZUMAN

Contents

The Most Important Equations. . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi

Chapter I

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Development of the Study of Structural Relations. . . . . . . 1 2. Classification of Structural Effects. . . . . . . . . . . . . . . . . . . . . 6 3. Techniques in the Polarographic Study of Structural Effects 10

Chapter II

General Equation for the Relation Between the Polarographic Half-Wave Potentials and Substituent Effects. . . . . . . .. . . . . . . 23

1. GeneraL........................................... 23 2. Influence of Polar Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3. Influence of Polar and Resonance Effects in Combination. 34 4. Influence of Polar and Steric Effects in Combination. . . . . . 37 5. The General Case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 6. The Role and Importance of the General Equation. . . . . . . 39 7. The Conditions for the Application of the General Equation 39

Chapter III

Benzene Derivatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2. Selection of Values of the Substituent Constants. .... . .. . 45

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3. Selection and Treatment of Half-Wave Potential Values.. 45 4. Reaction Series for which Equations (27), (31), and (37)

Hold...... ..................................... 56 5. Range of Validity of Equation (27); Significance of

Deviations for the Discussion of Electrode Process Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

6. Additivity of Substituent Effects. . . . . . . . . . . . . . . . . . . . . . 72 7. Application of the Constants (Jx and the Determination of

New Values of the Substituent Constants (Jx.......... 72 8. Ortho Derivatives-Application of Equation (37). . . . . . . 75 9. Hindrance of Co planarity due to Ortho Substituents... . . 85

10. The Question of Hydrogen Bonds in Ortho-Substituted Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

11. Factors Affecting the Reaction Constant P",R' . . . . . . . . . . 94 12. Other Empirical Relationships. . . . . . . . . . . . . . . . . . . . . . . 108 13. Applications of (27) and Related Equations. . . . . . . . . . . . 118

Chapter IV

Monocyclic Heterocyclic Compounds. . . . . . . . . . . . . . . . . . . . . . 131

1. GeneraL........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 2. Classification of Reaction Series. . . . . . . . . . . . . . . . . . . . . . . 133 3. Reducible Heterocyclic Rings. . . . . . . . . . . . . . . . . . . . . . . . . 139 4. Reduction in the Side Chain. . . . . . . . . . . . . . . . . . . . . . . . . . 148

Chapter V

Reaction Series in which the Electroactive Group is Directly Attached to an Alkyl or Aryl Substituent. . . . . . . . . . . . . . . . . . . 169

1. GeneraL.......................................... 169 2. Reactions for which Equations (25), (29), and (36) Hold. . 171 3. Effect of Changes in the Mechanism of the Electrode Pro­

cess Reflected in Deviations from Linear Free Energy Relations and Changes in the Sign of the Reaction Con-stant........................................... 181

4. Effect of Exchange of Methyl for Phenyl. . . . . . . . . . . . . . . 192 5. Effect of Transfer Coefficient. . . . . . . . . . . . . . . . . . . . . . . . . 195 6. Additivity of Substituent Effects. . . . . . . . . . . . . . . . . . . . . . 197 7. Factors Affecting the Value of the Reaction Constant

P;,R' ........................ , ............ " . .. . 199

Contents

8. Application of Equations (25) and (29) for the Determina­tion of New Values of the Substituent Constants

xv

ak and a~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 203 9. Other Empirical Quantitative Relations. . . . . . . . . . . . . .. 204

10. Two Functional Groupings in a Molecule... . . . . . . . . . .. 206

Chapter VI

Effects of Substituents in Condensed Polycyclic Hydrocarbons. 219

l. GeneraL........................................... 219 2. Classification of Reaction Series. . . . . . . . . . . . . . . . . . . . . .. 219 3. ElectroacLve Aromatic System with One Substituent. . . .. 229 4. Polysubstituted Electroactive Aromatic Systems. . . . . . . . . 231 5. Effects of a Substituent in a Condensed Aromatic Hydro­

carbon on the Reduction of a Functional Grouping in Another Position in the Ring System. . . . . . . . . . . . . . . .. 235

6. Effect of the Nature of the Aromatic Ring on Reduction in the Side-Chain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

7. Substituent in a Reducible Side-Chain. . . . . . . . . . . . . . . . . . 242

Chapter VII

Effects of Substituents in Polycyclic Heterocyclic Compounds. 247

1. GeneraL........................................... 247 2. Classification of Reaction Series. . . . . . . . . . . . . . . . . . . . . . . 247 3. Effect of a Substituent in an Electroactive Heterocyclic

Ring...... ............. ......................... 260 4. Effect of Substituents in the Benzene Ring and in Both

Rings on the Reduction of the Heterocyclic Ring. . . . . . 262 5. Effect of Substitution in a Phenyl Group Attached to

Electroactive Heterocyclic Ring. . . . . . . . . . . . . . . . . . . . . 266 6. Correlation of the Reactivities of Various Heterocyclic

Compounds by the Use of Dimroth Equation. . . . . . . . . 266 7. Effect of Substitution in the Heterocyclic Ring on Reduc-

tion in a Side-Chain on the Same Ring. . . . . . . . . . . . . . . 266 8. Effect of Substitution in the Benzene Ring on Reduction in

a Side-Chain on the Heterocyclic Ring. . . . . . . . . . . . . . . 267 9. Effect of the Position and Nature of the Heterocyclic Ring

on Reduction in the Side-Chain. . . . . . . . . . . . . . . . . . . . . 269

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Chapter VIII

Effects of Substituents in Quinonoid Compounds. . . . . . . . . . . .. 273

1. GeneraL........................................... 273 2. Classification of Reaction Series. . . . . . . . . . . . . . . . . . . . . .. 276 3. Monocyclic Quinonoid Systems. . . . . . . . . . .. . . . . . . . . . .. 280 4. Bicyclic Quinonoid Systems. . . . . . . . . . . . . . . . . . . . . . . . . .. 294 5. Polycyclic Quinonoid Systems. . . . . . . . . . . . . . . . . . . . . . . .. 302

Chapter IX

Alicyclic Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 309

1. Effects of Substituents in the Ring on an Electroactive Group Attached to the Ring. . . . . . . . . . . . . . . . . . . . . . .. 310

2. Effect of Ring Size and Type on an Electroactive Group Attached to the Ring. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 322

3. Effect of Ring Size and Type on Electroactive Groups that Form Part of the Cyclic System. . . . . . . . . . . . . . . . . . . .. 352

4. Conclusions........................................ 365

Author Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 367

Subject Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 375

The Most Important Equations

I1El/2 = P + M" + S (20) I1E 1/2 = P:,RO'~ + M" (33)

I1E 1/2 = p~,RO'k (25) I1El/2 = P",RO'X + o",R(Es)x (36)

IlEl/2 = P",R(JX (27) I1El/2 = P",R(Jo-X + o",R(Es)o-x (37)

I1E 1/2 = P:,RO'~ (29) I1E 1/2 = P",R'f.O'X (38)

I1El/2 = P",RO'X (30) I1El/2 = 'f.P~,RO'X (39a)

I1El/2 = P",RO'; (31) El/2 = P",RO'X + XP",R + K (44)

(El/2kx - (E 1/2 )l,H = P~[(El/2h,x - (E 1/2h,HJ (49)