25th International Congress Of Pure And Applied Chemistry. Plenary Lectures Presented At The 25th International Congress Of Pure And Applied Chemistry, Jerusalem, Israel 6–11 July 1975

Organizing Committee President: E. D. Bergman (deceased) Chairman: Y. Marcus Chairman of Scientific Committees : R. Mechoulan (Organic) M. Ottolenghi (Physical) S. Sarei (Medicinal) J. Epstein (Applied) Congress Editors : Y. Marcus L. Ben-Dor Members: S.Amiel F. Bergman M. R. Bloch J. Jortner S. Lifson R. Mechoulan A. Patchornick Z. Zurr D. Lavi e International Union of Pure and Applied Chemistry in conjunction with Israel Academy of Sciences and Humanities National Council for Research and Development and Israel Chemical Society 25th International Congress of Pure and Applied Chemistry Plenary lectures presented at the 25th International Congress of Pure and Applied Chemistry, Jerusalem, Israel 6-11 July 1975 Congress Editors: Y. Marcus and L. Ben-Dor The Hebrew University of Jerusalem PERGAMON PRESS OXFORD NEW YORK TORONTO SYDNEY PARIS FRANKFURT U.K. U.S.A. CANADA AUSTRALIA FRANCE WEST GERMANY Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 oBW, England Pergamon Press Inc.. Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. Pergamon of Canada Ltd., 75 The East Mall, Toronto, Ontario, Canada Pergamon Press (Aust.) Pty.Ltd., 19a Boundary Street, Rushcutters Bay, N.S.W. 2011, Australia Pergamon Press SARL, 24 rue des Ecoles, 75240 Paris, Cedex 05, France Pergamon Press GmbH,6242 Kronberg-Taunus, Pferdstrasse i, Frankfurt-am-Main, West Germany Copyright (c) 1977 International Union of Pure and Applied Chemistry All Rights Reserved. No part of this publication may be be reproduced, stored in a retrieval system or transmitted inany form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publishers The contents of this book appear in Pure and Applied Chemistry, Vol. 47, No. 1 (1976). Library of Congress Catalog Card No. 7 6 - 42131 Printed in Great Britain by A. Wheaton & Co., Exeter ISBN o 08 020952 1 Pure & Appi Chem., Vol. 47, pp. 1-10. Pergamon Press, 1976. Printed in Great Britain. AROMATIC PHOTOSUBSTITUTION REACTIONS1 E. HAVINGA and J. CORNELISSE Gorlaeus Laboratories, Leiden University, The Netherlands Abstract—In this paper attention is given primarily to substitution reactions of photoexcited aromatic compounds with (non-excited) nucleophiles. At the end a brief discussion is presented on the less-well known, but no less interesting photoinduced electrophilic substitution reactions, followed by a schematic representation of the various possible ways of heterolytic reaction of an electronically excited aromatic molecule. Nucleophilic aromatic photosubstitution nowadays comprises a great number and variety of reactions. Without ignoring traditional photochemical characteristics (singlet vs triplet reaction, 7τ->π* or η^>π* excitation etc.) the authors offer a systematization based mainly on the nature and influence of substituents (electron attracting or donating) in the aromatic system and on kinetic features. For certain types of aromatic photosubstitution the results obtained by chemical and spectroscopic investigations permit speculation on their mechanism. The variety and subtlety of the photoinduced aromatic substitutions seem to be no less than that of their thermal counterparts notwithstanding the fact that these reactions generally proceed extremely fast (not far from encounter controlled). As in thefieldof concerted processes, in heterolytic aromatic substitutions the thermal and the photochemical reactions mutually complement each other in a theoretically intriguing and practically useful way. variety of nucleophiles.3,5 The reactions often proceed to a high degree of conversion resulting in good yields of easily iso