Some Studies in Molecular Orbital Theory III. Substitution in Aromatic and Heteroaromatic Systems

Abstract

It is shown that LCAO molecular orbital theory, when combined with first‐order perturbation theory, provides a very simple procedure for estimating how far electronic effects will modify the transition state energies for substitution reactions in alternant molecules. This procedure is shown to lead to the same qualitative predictions as resonance theory, but has the advantage that it gives at the same time quantitative information as to the relative effects of substitution at different points in a complex system. The theoretical results agree well with experiment as far as can be ascertained at present. The approximations involved, and their relation to those of resonance theory, are discussed in detail.