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Preface IWO WIDELY R E A D TEXTS, The Anomeric Effect and Related Stereoelectronic Effects at Oxygen by Anthony J. Kirby, and Stereoelectronic Effects in Organic Chemistry by P. Deslongchamps, represent landmark treatises of a decade ago. The frequent use of these texts for upper-year undergraduate and graduate courses attests to the vitality and breadth of the science of stereoelectronic effects. In this area, the domains of synthetic, physical, inorganic, and theoret ical chemistry and enzymology meet and overlap. No theory is allowed to persist to the point of dogma unchallenged and without rigorous examina tion. Thus, this area is controversial and at times adversarial. In this field, often for the first time, students are confronted by a number of competing hypotheses with no established dogma to be safely memorized. Students are required to question theories, criticize conclusions, and understand the scope and limitations of a large number of modern experi mental and computational methods. Furthermore, the "true picture" presented by the pervasive and seductive images of computer-generated molecular modeling must be queried when confronted with stereoelec tronic effects. The object of this book is to provide a forum for competing viewpoints rather than to resolve the controversies surrounding the anomeric effect. Some of these viewpoints remain diametrically opposed. Although each chapter contains original research, the style is usually broader than that found in a traditional journal research paper. The range of techniques presented includes synthesis, kinetic analysis, crystal lography, N M R analysis, enzymology, and ab initio and molecular mechanics calculations. The book begins by describing the origins of the field with Lemieux's work in carbohydrate chemistry and the Edward-Lemieux effect. The second chapter sets the ground for the controversies to come. This chapter importantly emphasizes the significant scope and implications of the proposed stereoelectronic effects discussed in this book and provides references to those researchers who are not contributors. The following four chapters provide a forum for the major protagonists (or antagonists!) in this field who rely largely on the results of experimental approaches and have been intimately associated with the anomeric effect over the years. Two chapters follow from groups that integrate experi mental and theoretical methods. In subsequent chapters, three very dif ferent ab initio based theoretical methods are described, including ix In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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Weinhold's natural bond orbital analysis and Bader's theory of atoms in molecules. Although the anomeric effect specifically refers to carbohy drate chemistry, the scope of the associated stereoelectronic effects extends far beyond carbohydrate chemistry. Examples of applications in organometallic chemistry and for derivatives of sulfur and phosphorus oxyacids are presented in Chapters 12-14. The final chapter deals with the breakdown of molecular modeling methods in compounds influenced by stereoelectronic effects and subsequent efforts in reparameterizing molecular mechanics force fields. It is hoped that the intensity and vital ity of the presentations and the ensuing heated discussion at the sympo sium are faithfully mirrored in this book. Acknowledgments Of the many people involved with this book, I thank, in addition to the authors: Vernon Box, Russ Boyd, Bruce Branchaud, Chris Cramer, Richard Franck, Alfred French, Moses Kaloustian, Victor Marquez, Mor ten Meldal, Martin Tessler, Kenneth Wiberg, Steve Withers, and, in par ticular, Walter Szarek. I also thank the Division of Carbohydrate Chem istry of the American Chemical Society for sponsorship and the donors of the Petroleum Research Fund of the American Chemical Society for par tial funding of the symposium. G R E G O R Y R. J. T H A T C H E R
Department of Chemistry Queen's University Kingston, Ontario K7L 3N6 Canada July 6, 1993
χ In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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Introduction I N 1977 A SYMPOSIUM ENTITLED "Origin and Consequences of the Anomeric Effect" was organized by Derek Horton and me and cosponsored by the Division of Carbohydrate Chemistry of the American Chemi cal Society (ACS) and the Organic Chemistry Division of the Chemical Institute of Canada (CIC). The symposium was part of the Second Joint Conference of the A C S and CIC in Montreal, Quebec, Canada. This symposium was the first devoted exclusively to a discussion of the anomeric effect, and it provided a mechanism for interactions among a variety of chemists, namely, theoreticians, structural chemists, physical organic chemists, and synthetic chemists. The material presented at that symposium, together with some new interpretations by the speakers that resulted from these interactions, formed the basis of A C S Symposium Series 87, Anomeric Effect: Origin and Consequences. Fifteen years after the Montreal symposium, the A C S Division of Carbohydrate Chemistry sponsored a second symposium on the anomeric effect. Greg Thatcher organized this symposium as part of the 204th A C S National Meeting in Washington, D C . The Washington symposium again involved diverse types of chemists, and the presentations again evoked vigorous discussions among the participants. The 15-year period between the two symposia has witnessed many developments in the area of the anomeric effect involving not only new theoretical interpretations and computational approaches, but also struc ture and reactivity relationships that have far-reaching significance, for example, in enzymology and synthetic chemistry. However, the dominant feature that emerged from the Washington symposium was that our current degree of theoretical understanding of the anomeric effect still does not provide a totally integrated and quantitatively predictive theory. This book provides a stimulating overview of recent developments and captures the spirit of the continuing investigation of an important phenomenon. WALTER A. SZAREK
Department of Chemistry Queen's University Kingston, Ontario K7L 3N6 Canada R E C E I V E D July 19, 1993 xi In The Anomeric Effect and Associated Stereoelectronic Effects; Thatcher, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
