MCD of non-aromatic cyclic π-electron systems. Part 1. The perimeter model for antiaromatic 4N-electron [n]annulene biradicals1

Abstract

The LCAO version of the perimeter model with overlap through second order is used to obtain algebraic solutions for the singlet electronic states of the antiaromatic 4N-electron [n]annulenes of D_nh symmetry. The states of these biradicals are classified and their spectroscopic properties derived. General simple results are given for the signs and magnitudes of the A, B and C terms in magnetic circular dichroism. The effects of perturbations that preserve the antiaromatic biradical or biradicaloid character are considered. Other perturbations will be treated in Parts 2 and 3.