The Nonclassical Ion Problem

mE NONCLASSICAL ION PROBLEM mE NONCLASSICAL ION PROBLEM Herbert C. Brown Purdue University West Lafayette, Indiana With comments by Paul von R. Schleyer University of Erlangen-Nurnberg Erlangen, West Germany Plenum Press • New York and London Library of Congress Cataloging in Publication Data Brown, Herbert Charles, 1912The nonclassical ion problem. Includes index. 1. Carbonium ions. I. Schleyer,PaulvonR.,1930II. Title. QD305.C3B 76 547.7 76-45175 ISBN-13:978-1-4613-4120-8 e-ISBN-13:978-1-4613-4118-5 DOl: 10_1007/978-1-4613-4118-5 ©1977 Plenum Press, New York Softcover reprint of the hardcover 1st edition 1977 A Division of Plenum PufJlishing Corporation 227 West 17th Street, New York, N. Y. 10011 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher To a fascinating, seductive intermediate, the 2-norbornyl cation, and to my wonderful wife, who cheerfully coped. Acknowledgments The author is deeply indebted to Professor Paul von Rague Schleyer, with whom a continuous discussion on a scientific level was maintained for many years, even though each of us occasionally arrived at different conclusions; to Dr. M. Ravindranathan, who gave exceptional assistance in preparing the drawings, checking the references and manuscript, and in assisting with the pUblication; and to Annette Wortman, who did her usual superlative job in typing the manuscript. H.CB. The commentator has been debating the subject of nonclassical ions with Professor Brown privately for more than a decade. Our letters fill a large volume, and I am only one of the many persons with whom he has had an extensive correspondence! I must confess that many of his writings, published and unpublished, have infuriated me and have on occasion elicited intemperate responses. Nevertheless, communication has remained open and I feel that real progress in understanding the nature of carbocations has been made during this period. My own position has undergone considerable change, as has that of Professor Brown. However, we still diverge in our views of this topic. In our discussions, it is inevitable that areas of disagreement are emphasized more than areas of agreement, although the latter are large. It is very much to Professor Brown's credit that he has repeatedly attempted to arrange both open and published debates on the subject of nonclassical ions. Professor Olah has presented his viewpoint, but I have remained silent. I wish to thank Professor Brown, not only for the chance to comment on the chapters of this book, but also for his hospitality during visits to Purdue University, where most of these comments were written. The manuscript was completed during the tenure of an Adjunct Professor vii viii Acknowledgments appointment at Case Western Reserve University, and benefited from helpful suggestions provided by Professor J. E. Nordlander and Professor G. A. Olah. P.v.R.S. Preface In the early 1950s it was proposed that the cationic centers of carboniun ions in the usual solvolytic media could diminish their electron deficiency by interacting with the - CH 2 0{3Ns C>- CH2 =CH CH,oCH 3 I CH2 CH2 0CH3 O.lM CH3 0H CH3 0Na (0.11 M) 0- 25"C rn;rnt 93% 94% 66 69 31 28 3 2 (8) 25"C O.8Ns -CH30H O.lM CH3 0H 100% CH3 0Na (0.11 M) 100% 48 47 47 47 5 6 The results are not compatible with the production of a single (1"bridged intermediate, such as 2. It is compatible with the production