Aromaticity and Optical Activity

Abstract

The relationship between aromaticity and optical activity is investigated in comparisons of heterocycles with 4n + 2 and 4n π-electrons, in cyclic ketones with and without aromatic resonance structure representations, in tautomers and pericyclic reaction partners in which only one compound of each pair is aromatic, and in partially hydrogenated cyclo-C18 derivatives with both radial and tangential π-orbitals. In all comparisons, aromaticity is correlated to diminished optical activity. A heuristic explanation of this observation is grounded in the electric dipole-magnetic dipole polarizability contribution to optical activity in which the sense of electric dipoles and magnetic dipoles become uncoupled when electrons can circulate around a ring with either sense. These observations form a basis for making broad structure-optical activity correlations from inspection of molecular structure.