The activation strain model of chemical reactivity

Herein, we provide an account of the activation strain model of chemical reactivity and its recent applications. In this model, the potential energy surface DE(zeta) along the reaction coordinate zeta is decomposed into the strain Delta E-strain(z) of the increasingly deformed reactants plus the interaction Delta E-int(zeta) between these deformed reactants, i.e., Delta E(zeta) = Delta E-strain(zeta) + Delta E-int(z). The purpose of this fragment-based approach is to arrive at a qualitative understanding, based on accurate calculations, of the trends in activation barriers and transition-state geometries (e.g., early or late along the reaction coordinate) in terms of the reactants' properties. The usage of the activation strain model is illustrated by a number of concrete applications, by us and others, in the fields of catalysis and organic chemistry.