A perimeter model for the magnetic properties of some non-benzenoid aromatic hydrocarbons

Abstract

Pullman applied London's method of calculating diamagnetic susceptibilities to some cata-condensed aromatic hydrocarbons with 4v carbon atoms. He found that the magnetic properties of these compounds should be quite different from the magnetic properties of cata-condensed aromatic hydrocarbons with (4v + 2) carbon atoms. The existing experimental data seem to confirm these predictions, at least qualitatively. Pauling's ring current model is of very limited use, when applied to 4v-systems. A simplified LCAO-MO treatment outlined here enables one to understand these results more readily. A cyclic chain of 4v sp²-hybridized carbon atoms is first subjected to a homogeneous magnetic field perpendicular to the molecular plane. Appropriate cross-links are then ‘formed’ and treated as a perturbation. A formula is given from which the diamagnetic anisotropy is easily estimated.