CLASSIFICATION OF SUBSTITUENTS BY SIGMA-ELECTRON AND PI-ELECTRON ENERGY SEPARATION

The previously introduced sigma and pi energy separation is extended t o subsystems. sigma and pi electron donor and acceptor properties of t he substituents are tested with a Lowdin population analysis. The infl uence of the substituents on the sigma and pi electron energies is cal culated for substituted benzene, cyclobutadiene, butadiene, and borazi ne. A linear relationship is found which shows that an increase of sig ma electron energy is accompanied by a decrease in pi electron energy and vice versa. This allows a classification of substituent groups in terms of reactivity. (C) 1994 John Wiley & Sons, Inc.