The valence bond diagram approach: A paradigm for chemical reactivity

This chapter describes a new-generation valence bond (VB) paradigm. VB theory is a new-old theory. Until the mid-1950s, it has dominated the mental map of chemists. Then it fell into disrepute, the mental map was recharted, and the wisdom of VB theory has been written over by other theories. With just two figures the VB diagram model describes both barrier formation in a single chemical step and chemical mechanisms. It thereby forms a basis for a unified system of thought about chemical reactivity. The emergence of new VB methodologies strengthens the model by providing a quantitative description of VB diagrams. The chapter outlines a guide to the qualitative use of the model by discussing a variety of applications, to radical reactions, reactions of electrophiles and nucleophiles, cycloadditions, bond activation by transition metal catalysts, new reaction mechanisms, photochemical reactions, and so on.