Complete account of the π-electron correlation in calculating ring currents in conjugated aromatic and antiaromatic systems

Abstract

A semiempirical theory of ring π currents is developed, which accurately takes into account the electron correlation using the full configuration interaction (FCI) method. An elementary model is proposed, in which the calculation of the π-electron correlation is reduced to the model of generalized alternative Huckel systems. The FCI and SCF (self-consistent field) methods are used to calculate the diamagnetic susceptibilities and ring currents for some typical π systems. It is shown that, as a rule, the SCF method allows the qualitatively true description of the magnetic properties of condensed systems, although for antiaromatic molecules it often yields underestimated values of paramagnetic currents. The results of the FCI calculations suggest that electronic excitations can induce transitions from π paramagnetism to π diamagnetism (e.g., in fulvenes) and back (in quinones).