Page 9 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

Introduction

This volume is intended for students who have completed the equivalent of a
two-semester introductory course in organic chemistry and wish to expand their under-
standing of structure and reaction mechanisms in organic chemistry. The text assumes
basic knowledge of physical and inorganic chemistry at the advanced undergraduate
level.
Chapter 1 begins by reviewing the familiar Lewis approach to structure and
bonding. Lewis’s concept of electron pair bonds, as extended by adding the ideas of
hybridization and resonance, plus fundamental atomic properties such as electroneg-
ativity and polarizability provide a solid foundation for qualitative descriptions of
trends in reactivity. In polar reactions, for example, the molecular properties of acidity,
basicity, nucleophilicity, and electrophilicity can all be related to information embodied
in Lewis structures. The chapter continues with the more quantitative descriptions of
molecular structure and properties that are obtained by quantum mechanical calcula-
tions. Hückel, semiempirical, and ab initio molecular orbital (MO) calculations, as well
as density functional theory (DFT) are described and illustrated with examples. This
material is presented at a level sufficient for students to recognize the various methods
and their ranges of application. Computational methods can often provide insight
into reaction mechanisms by describing the structural features of intermediates and
transition structures. Another powerful aspect of computational methods is their ability
to represent electron density. Various methods of describing electron density, including
graphical representations, are outlined in this chapter and applied throughout the
remainder of the text. Chapter 2 explores the two structural levels of stereochemistry—
configuration and conformation. Molecular conformation is important in its own right,
but can also influence reactivity. The structural relationships between stereoisomers and
the origin and consequences of molecular chirality are discussed. After reviewing the
classical approach to resolving racemic mixtures, modern methods for chromatographic
separation and kinetic resolution are described. The chapter also explores how stereo-
chemistry affects reactivity with examples of diastereoselective and enantioselective
reactions, especially those involving addition to carbonyl groups. Much of today’s work
in organic chemistry focuses on enantioselective reagents and catalysts. The enantio-
selectivity of these reagents usually involves rather small and sometimes subtle differ-
ences in intermolecular interactions. Several of the best-understood enantioselective
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