A simple molecular orbital perturbation treatment of the switching of bond order patterns within molecular systems

Abstract

A simple molecular orbital perturbation method for determining the effects of disturbances in molecular systems is applied to predict the conditions required for small perturbations of the energy to produce major changes in individual bond orders. The results are used to explain several important physical and chemical observations concerning quantitative linear correlations which are puzzling when considered in terms of commonly used theoretical models. Their implications for simple resonance theory are also discussed. It is concluded that effects of mutual conjugation are not the principal source of differences between the various empirical scales of substituent effects on properties of benzene and its derivatives.