Aromatic electrophilic substitution. A modern valence bond study

Abstract

The Hartree–Fock, spin-coupled valence bond and complete active space self-consistent field methods are used to study the electronic structure of benzene, phenol, benzonitrile and their protonated arenium intermediates. The spin-coupled wavefunctions for these systems can be readily interpreted in terms of the well known classical valence bond resonance structures. However, the charge delocalization in the arenium ions is not achieved through a resonance mechanism which must invoked if a localized orbital description is adopted, but through a single spatial configuration of semi-delocalized orbitals. The effect of the substituents on the energy and the electron distribution of the arenium intermediates is borne out in a clear and visual way by the form of a spin-coupled wavefunction for these systems.