Introduction

The transition state (TS) is the critical configuration of a reaction system situated at the highest point of the most favorable reaction path on the potential-energy surface. It is regarded as critical in the sense that if it is attained the system will have a high probability of continuing reaction to completion. This chapter outlines the kind of insight into the TS gained by molecular-orbital computations. It presents few examples of TS geometries for either familiar prototypes or unique patterns of elementary reactions. The chapter discusses some dynamic aspects of the TS. For HNO₂, the TS is by no means a radical pair. The TS theory is a statistical theory that predicts the magnitude of the preexponential factors for the rate constants of physical and chemical rate processes. The chapter also presents an overview of the key concepts discussed in this book.