A new theoretical approach to the empirical resonance energies of the aromatic hydrocarbons

Abstract

In the framework of the Hückel MO approximation, the differences in total binding energy between a given molecule and the corresponding distorted Kekulé-type structure are calculated for a variety of benzenoid hydrocarbons. The total binding energy is assumed to be given by the sum of the π-electron and σ-electron binding energies. It is shown that there is a good linear relationship between the calculated differences in total binding energy and the π-electron delocalization energies (DE) as obtained by using the simple Hückel MO method. This provides a physical basis for the use of the π-electron DE as a theoretical index to the empirical resonance energy (RE). Further, by examining the changes in π-electron binding energy between a given molecule and the corresponding distorted Kekulé-type structure, it is concluded that in benzenoid hydrocarbons the main contributor to the RE is not the π-electron DE but the compressional energy of σ bonds.