The n??* optical activity of chiral carbonyl compounds predicted to be optically inactive by the octant rule

Abstract

The “one-electron” model of n→π* optical activity in chiral carbonyl compounds is carried to second-order in perturbation theory and the results are applied to systems which are predicted by the octant rule to yield zero n→π* optical activity. It is shown that second-order contributions to the n→π* rotatory strength lead to sector rules which are qualitatively different from those obtained from first-order contributions. Inclusion of three-way interactions involving the carbonyl chromophore and two different extrachromophoric perturbing groups (or atoms) lead to second-order contributions to the rotatory strength which can account for the n→π* optical activity in chiral carbonyl systems predicted to be optically inactive by the conventional quadrant and octant rules. These results are shown to be in agreement with the conclusions derived by Ruch and Schonhofer from a purely algebraic theory of molecular chirality.