This book is intended as a text for undergraduate and first-year graduate students who have completed a one-year course in organic chemistry. Its aim is to provide a structure that will help the student to organize and interrelate ,. the factual information obtained in the earlier course and serve as a basis for ‘L 1 , study in greater depth of individual organic reactions and of methods by which chemists obtain information about chemical processes.
The primary focus of the book is on reaction mechanisms, not only because knowledge of mechanism is essential toÂ understanding chemical processes but also because theories about reaction mechanisms can explain diverse chemical
phenomena in terms of a relatively small number of general principles. It is this latter capability of mechanistic theory which makes it important as an organizing device for the subject of organic chemistry as a whole.
In treating mechanisms of the important classes of organic reactions, we have tried to emphasize the experimental evidence upon which mechanistic ideas are built and to point out areas of uncertainty and controversy where more work still needs to be done. In this way we hope to avoid giving the impression that all organic mechanisms are well understood and completely agreed upon but instead to convey the idea that the field is a dynamic one, stillm very much alive and filled with surprises, excitement, and knotty problems.
The organization of the book is traditional. We have, however, b2en’ selective in our choice of topics in order to be able to devote a significant portion of the book to the pericyclic reaction theory and its applications and to include a chapter on photochemistry. The pericyclic theory is certainly the most important development in mechanistic organic chemistry in the past ten years. Because it is our belief that x Preface the ideas and method of thinking associated with the pericyclic theory will have an increasing impact in both organic and inorganic chemistry in the future, we have given a more detailed discussion of its purely theoretical aspects than has heretofore been customary in books of this kind. This discussion includes both the Woodward-Hoffmann approach and the Dewar-Zimmerman aromaticity approach and makes the connection between them. Our treatment requires as background a more sophisticated understanding of covalent bonding than is ordinarily given in introductory courses; we have therefore included an extensive presentation of bonding theory. It begins at a basic level with a review of familiar concepts in Chapter 1 and introduces in Chapter 10 the terminology and ideas needed to understand the pericyclic theory and its ramifications. The treatment is qualitative throughout. Although quantitative molecular orbital calculations are not needed for our purposes, Appendix 2 to Chapter 1 summarizes the molecular orbital calculation methods in general use. The Hiickel
MO method is covered in sufficient detail to allow the reader to apply it to simple systems.
Another innovation in this text is the use of three-dimensional reaction coordinate diagrams, pioneered by Thornton, More O’Ferrall, and Jencks, in the discussions of nucleophilic substitutions, eliminations, and acid catalysis of carbonyl additions. We hope that the examples may lead to more widespread use of these highly informative diagrams.
A chapter on photochemistry provides a discussion of photophysical processes needed as background for this increasingly important area of chemistry and treats the main categories of light-induced reactions, The text assumes elementary knowledge of the common organic spectroscopic techniques. Nevertheless, we have included a description of the recently developed method of chemically induced dynamic nuclear polarization (CIDNP), which has already proved to be of great importance in the study of radical reactions and which has not yet found its way into books covering spectroscopy of organic compounds.
Problems of varying difficulty have been included at the ends of the chapters. Some problems illustrate points discussed in the text, but others are meant to extend the text by leading the student to investigate reactions, or
even whole categories of reactions, which we have had to omit because of limitations of space. References to review articles and to original literature are given for all problems except those restricted to illustration of points that the
text discusses in detail. Problems that represent significant extensions of the text are included in the index. The book is extensively footnoted. It is neither possible nor desirable in a book of this kind to present exhaustive reviews of the topics taken up, and we have made no effort to give complete references. We have tried to include references to review articles and monographs wherever recent ones are available, to provide key references to the original literature for the ideas discussed, and to give sources for all factual information presented. The text also contains numerous cross references. The amount of material included is sufficient for a full-year course. For a one-semester course, after review of the first two chapters, material may be chosen to emphasize heterolytic reactions (Chapters 3-8), to cover a broader
Preface xi range including radicals and photochemistry (selections from Chapters 3-8 plus 9 and 13), or to focus primarily on pericyclic reactions (Chapters 10-12).
In selecting material for a one-semester course, the following sections should be considered for possible omission : 3.5, 4.4, 4.5, 5.6, 6.3, 7.3, 7.5, 8.3, 9.5, 10.4, 11.6, 11.7. MTe would like to thank the following people for reviewing parts of the manuscript and for providing helpful comments: Professors D. E. Applequist, C. W. Beck, J. C. Gilbert, R. W. Holder, W. P. Jencks, J. R. Keeffe, C. Levin, F. B. Mallory, D. R. McKelvey, N. A. Porter, P. v. R. Schleyer, J. Swenton,
and T. T. Tidwell. We are particularly grateful to Professor N. A. Porter, who reviewed and commented on the entire manuscript. We owe special thanks to Professor Charles Levin for many enlightening discussions and to Carol Dempster for essential help and encouragement.
Thomas H. Lowry
Kathleen Schueller Richardson