On the Molecular-Orbital Theory of Conjugated Organic Compounds with Application to the Perturbed Benzene Ring

Abstract

The electronic structure of a molecular system is investigated by using the idea of molecular orbitals. The behavior of the separate molecular orbitals and the orbital energies under the influence of the substitution of one or more heteroatoms, considered as perturbations, is examined. A series of quantities, separate charge orders, bond orders, and mutabilities are introduced, giving information about some characteristic physical and chemical properties of the compound. The perturbation scheme is carried out explicitly to the second order in the energies and to the first order in the orbitals, and special attention is paid to the treatment of degenerate levels. The overlapping problem is fully discussed. The basic results are independent of any empirical parameters, and they may be used either in the naïve semi‐empirical theory or in a more elaborate theoretical approach based on an antisymmetrized molecular wave function. As an example, numerical applications are carried out in detail on benzene. Separate charge orders, bond orders, and mutabilities are tabulated, and orbital energies for a perturbed benzene ring with one or two heteroatoms are explicitly given.