The fundamentals of organic chemistry have been discussed in part one of the book which includes structures, isomerism and nomenclature of organic compounds (chapter 1), how the structures are formed (chapter 2), symmetry of organic mol- ecules (chapter 3) and how organic compounds react (chapter 4). Immediately following these chapters of basic organic chemistry, a systematic treatment of the general hydrocarbons has been given in chapter 5, 'Alkanes, Cycloalkanes and Aromatic Hydrocarbons".

In solution, all participants in a chemical reaction are solvated: the reactants and the products-and the transition state. Our examination of these must include any solvent molecules that help make up the structures and help determine their stabili- ties. And so in Chapter 4, using as our examples the nucleophilic substitution reac- tions the students have just studied, we show how reactivity-and, with it, the course of reaction-is affected by the solvent. We show just how enormous solvent effects can be: that the presence of a solvent can speed up-or slow down-a reaction by a factor of 1020; that a change from one solvent to another can bring about a million fold change in reaction rate.

At the same time, in Chapter 4, the students are becoming acquainted with sec- ondary bonding. They learn that these forces-ion-dipole, dipole-dipole, van der Waals are involved in much more than solvent effects. They learn that, acting not only between different molecules but between different parts of the same molecule, secondary bonding plays a key role in determining the shapes of large molecules like proteins and DNA, shapes that determine, in turn, their biological properties. The same forces that bring about dissolution of a solute in a solvent also make the DNA helix double and enable an enzyme to hold a substrate.

It is becoming increasingly clear that any examination of a molecular structure must be three dimensional. To emphasize this, and to help guide the student through this complex area of organic chemistry, we introduce the principle of stereochem- istry in three stages. In Chapter 5AII and 5BII, we present the fundamentals of stereoisomerism. In Chapter 18E, we deal with the concepts of stereoselectivity and stereospecificity. We show how stereochemistry helps us to understand reaction mech- anisms; how this understanding can be used to control the stereochemical outcome of a reaction; and why we want to exercise this control-because the stereospecificity of biological reactions demands an equal stereoselectivity in the synthesis of drugs and hormones and pheromones.