Advances in Physical Organic Chemistry This Page Intentionally Left Blank Advances in Physical Organic Chemistry . Edited by V. GOLD Department of Chemistry King’s College, University of London VOLUME 6 1968 Academic Press, London and New York ACADEMIC PRESS INC. (LONDON) LTD. Berkeley Square House Berkeley Square, London, W.l. U.S.Edition published by ACADEMIC PRESS INC. 111 Fifth Avenue New York, New York 10003 Copyright 0 1968 by Academic Press Inc. (London) Ltd. All Rights Reserved No part of this book may be reproduced in any form by photostat, microam, or any other means, without written permission from the publishers Library of Congress Catalog Card Number :62-22125 PRINTED IN UREAT BRITAIN BY SPOTTISWOODE, B A L L A m Y N E AND COMPANY LIMITED LONDON AND COLCHESTER CONTRIBUTORS TO VOLUME 6 E. K. FIELDS, Research an& Development Department, Amoco Chemicals Corporation, Whiting, Indiana, U.S.A. M. M. KREEVOY, School of Chemistry, University of Minnesota, Minneapolis, Minnesota, U.S.A. S. MEYERSON,Research and Development Department, American Oil Company, Whiting, Indiana, U.S.A. S. I. MILLER, Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois, U.8.A. H. A. SOHERAGA, Department of Chemistry, Cornell University, I t h a , New York 14850, U.S.A. J. M. WILLIAMS, Jr.,School of chemistry, University of Minnesota, Minneapolis, ktinnesota, U.S.A. This Page Intentionally Left Blank CONTENTS CONTRIBUTORS TO VOLUME 6 . V Mechanisms of Formation and Reactions of Arynes at High Temperatures E. K. FIELDS and S. MEYERSON I. Introduction . 11. Arynes from Aromatic Anhydrides . . A. Reactions of Benzyne with Benzene B. Reactions of Benzyne with Deuteriated Benzenes . C. Arynes from Aromatic Anhydrides Other Than Phthalic . D. Reactions with Chlorinated Benzenes . E. Reactions with Pyridine . F. Reactions with Thiophene and Benzothiophene . G. Reactions of Tetraphenylbenzyne from Tetraphenylphthalic Anhydride . 111. Benzyne from o-Sulfobenzoic Anhydride . IV. Benzyne from Acetylene . V. Conclusion . References . 16 21 26 32 46 50 64 67 58 Developments in the Study of A 4 2 Reactions in Aqueous Solution J . M. WILLIAMS, JR. and M. M. KREEVOY . I. Introduction 11. Gross Mechanism . A. Identification of Proton Transfer as the Rate-Determining Step . B. Pre Rate-Determining Steps C, Multiple Rate-Determining Processes . 63 64 64 79 83 viii CONTENTS 111. Details of Mechanism . A. Structure of the Starting State . B. Direct versus Indirect Proton Transfer . C. Detailed Structure of Intermediates . D. Substituent Effects on Reactivity and the Electronic Structure of the Transition State . E. Non-Adiabatic Processes . IV. Conclusions, Apologies, and Acknowledgments . References . a5 85 88 92 94 95 97 98 Calculations of Conformations of Polypeptides H. A. SCHERAGA I. Introduction . 11. Conventions . 111. Geometrical Data IV. Transformation of Coordinates . V. Terms Contributing to the Expression for the Total Energy . A. Torsional Energies . B. Nonbonded Interactions . C. Electrostatic Interactions . D. HydrogenBond . E. Distortion of Geometry . F. Role of Crystal Energy Calculations in Refinement of Energy Parameters . G. Free Energy of Hydration . H. Loop-Closing Potential . VI. Methods of Energy Calculation and Energy Minimization A. Hard-Sphere Potential . B. Complete Energy Expression VII. Results with Hard-Sphere Potential . VIII. Application of Complete Energy Expression to Results Obtained from the Hard-Sphere Potential . IX. Use of Complete Energy Expression for Conformational Energy Calculations, Including Energy Minimiza