Model of organic reactivity that generates a reaction profile from curves that describe the energies of reactant, product, and intermediate electronic configurations (or, alternatively, reactant, product and intermediate electronic states) as a function of the reaction coordinate. The crossing reflects the electronic reorganization that accompanies the transformation of reactants and products.
Source:
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1933 (https://doi.org/10.1351/pac199971101919)