Orbital Symmetry And Reaction Mechanism

Criteria of orbital symmetry conservation had a profound influence on mechanistic thinking in organic chemistry and are still commonly applied today. The author presents a coherent set of operational rules for the analysis of scope and reliability. It is written from the viewpoint of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). Its advantage lies in its provision of a coherent overview of the relation between symmetry and mechanism. For reasons of consistency, the book remains within the framework of molecular orbital theory.

First published in 1979 as the second edition of a 1972 original, this textbook provides a systematic account of an important area of organic chemistry - that of cycloadditions and molecular rearrangements. The necessary theoretical background for understanding these reactions is presented in non-mathematical form and various alternative approaches to the theory are compared. The core of the book is a descriptive account of various types of cycloaddition and rearrangement reactions. The synthetic importance of these reactions is emphasised and, by providing the mechanistic background, the book demonstrates to the reader the relationship between the different types of reactions. This book will be of value to anyone with an interest in organic chemistry.

Orbital Symmetry: A Problem-Solving Approach was born of the necessity to present to students Woodward and Hoffmann's approach to pericyclic reactions. Hence the tone is introductory, and the book is addressed primarily to an audience of advanced undergraduate and beginning graduate students. The text seeks to familiarize the readers with several of the more often encountered methods of analyzing pericyclic reactions, and these methods should enable the analysis of virtually all of them. Problem solving is the foundation of the approach. Both the introductory and theory sections include problems to prepare the reader for the more extensive chapters of problems that follow. All problems (except those in Chapter VII) are answered in the text and are fully referenced where appropriate. Many of the problems require the use of molecular models if they are to be appreciated. Prentice-Hall's ""Framework Molecular Models"" and Benjamin's ""Maruzen Models"" are best suited for the construction of the highly strained molecules often encountered in the problems, and their use is recommended.

The Conservation of Orbital Symmetry examines the principle of conservation of orbital symmetry and its use. The central content of the principle was that reactions occur readily when there is congruence between orbital symmetry characteristics of reactants and products, and only with difficulty when that congruence does not obtain—or to put it more succinctly, orbital symmetry is conserved in concerted reaction. This principle is expected to endure, whatever the language in which it may be couched, or whatever greater precision may be developed in its application and extension. The book opens with a review of the elementary aspects of the molecular orbital theory of bonding. This is followed by separate chapters on correlation diagrams, the conservation of orbital symmetry, theory of electrocyclic reactions, theory of cycloadditions and cycloreversions, and theory of sigmatropic reactions. Subsequent chapters deal with group transfers and eliminations; secondary conformational effects in concerted cycloaddition reactions; and generalized selection rules for pericyclic reactions.

??1???1??orbita1 theory has had some notable successes in the ana1ysis of individua1 organic reactions and in corre1ations between reaction series. Gen???ll? the theory has???? invoked to exp1ain known chemica1 phenomena, and rather infrequent1y [?? broad1y-based predictions. In 1965 Woodward and??????? published? series of papers?? the??1???1??orbita1 inter pretation of various types of concerted cyc10-addition reactions, which hitherto had???? rather????1? understood. Because these processes (now known as pericyclic reactions) had great synthetic importance, and because the Woodward-Hoffmann theory was stated so explicit1y as to allow [?? usefu1 and far-reaching predictions to?? made, the genera1 acceptance of the so-called Woodward-Hoffmann Ru1es was very rapid. Judging from the vast number of publications that have appeared,? great dea1 of experimentaleffort has???? channelled into this genera1 area since that time, the results of which provide? vindication of the ru1es. The theoretica1 basis of Woodward and Hoffmann's method has, however,???? the subject of criticism and controversy, and??????? of alternative theoretica1 methods have a1so appeared.???? university departments (inc1uding?ur own) have for some time covered pericyclic reactions in their undergraduate and graduate courses. Because aims, teaching methods, and persona1 preferences differ wide1y, each of the various theoretica1 methods have achieved some currency. We have sought to?1??? these methods in some sort of perspective. The book is intended to?? introductory, being aimed primarily at fina1 year undergraduates and first year postgraduates.

The elucidation of reaction mechanisms generally requires the carefully designed control of molecular symmetry to distinguish between the many possible reaction pathways. Making and Breaking Symmetry in Chemistry emphasises the crucial role played by symmetry in modern synthetic chemistry. After discussion of a number of famous classical experiments, the advances brought about by the introduction of new techniques, in particular NMR spectroscopy, are exemplified in numerous cases taken from the recent literature. Experimental verification of many of the predictions made in Woodward and Hoffmann's explication of the Conservation of Orbital Symmetry are described. Applications that involve the breaking of molecular symmetry to resolve these and other mechanistic problems in organic, inorganic and organometallic chemistry are presented in the first sections of the book, together with many examples of the detection of hitherto hidden rearrangement processes.Subsequently, under the aegis of making molecular symmetry, examples of the preparation of highly symmetrical molecules found in the organic, organometallic or inorganic domains are discussed. These include Platonic hydrocarbons or boranes, tetrahedranes, cubanes, prismanes, dodecahedrane, fullerene fragments such as corannulene, sumanene or semibuckminsterfullerene, and other systems of unusual geometries or bonding characteristics (Möbius strips, molecular brakes and gears, Chauvin's carbomers, Fitjer's rotanes, persubstituted rings, metal-metal multiple bonds, etc.). The text also contains vignettes of many of the scientists who made these major advances, as well as short sections that briefly summarise key features of important topics that underpin the more descriptive material. These include some aspects of chirality, NMR spectroscopy, and the use of isotopic substitution to break molecular symmetry. A brief appendix on point group symmetry and nomenclature is also helpfully provided.

Pericyclic Reactions, Volume 1 covers the theoretical approaches to pericyclic reactions and pericyclic reactions of reactive intermediates and of particular reaction types. The book discusses the operational criteria for evaluation of concertedness in potential pericyclic reactions; and the Mobius-Hückel treatment of organic systems and reactions and molecular orbital following as a technique in organic chemistry. The text also describes some pericyclic reactions of carbenes and carbanions. Physicists and people involved in the study of pericyclic reactions will find the book invaluable.