1.3 Modelling Radicals and Their Reactivities

Abstract

In this chapter, the application of computational quantum mechanical methods to the understanding of radical reactions is introduced. For radical reactions, access to electronic configurations through quantum chemical calculations allows rationalization of unusual reactivities. Using the valence bond approach, the nature of bonding in three-electron bonds can be characterized by large resonance interactions. Similarly, some simple reactions that are commonly believed to be radical-free, such as [3 + 2] cycloadditions, are in fact governed by a high-lying biradical intermediate that helps to stabilize the transition state. More complex radical and enzymatic reactions can also be modelled, as illustrated by the example of horseradish peroxidase. These case studies show that computational analysis can complement experimental investigations and fill in the blanks to enable a more complete understanding of radical reactions.