Abstract

The reaction force F(xi) is the negative gradient of the potential energy of a chemical process along the intrinsic reaction coordinate xi. We extend the rigorous concept of F(xi) to the activation strain model of Bickelhaupt et al., to formulate the strain force F-str(xi) that retards a reaction and the interaction force F-int(xi) that drives it. These are investigated for a group of Diels-Alder cycloadditions. The results fully support the interpretation of the minimum of F(xi) as defining the beginning of the transition from deformed reactants to eventual products.