Molecular orbital calculations of aromatic reactivity. Part I. π-Electron calculations for monosubstituted benzenes

Abstract

The principles underlying the calculations of activation energies for electrophilic aromatic substitution are examined. Hückel and self-consistent-field methods have been used to calculate localisation energies and electron distributions for the ground state and for transition states for ortho-, meta-, and para-substitution in some mono-substituted benzenes. The localisation energies fail to predict correctly the observed results by either method. Correlation with σ⁺ values is better with the Hückel than the SCF method, but this is considered fortuitous.