Aromaticity, polarisability and ring current

Electric dipole polarisability has been proposed as an alternative to magnetic criteria of aromaticity. The ipsocentric formulation of the molecular response to a magnetic field gives selection rules for diatropic ring current that coincide with those for in-plane polarisability. Thus, induced pi current strength might correlate, if at all, with HOMO contributions to the in-plane components of polarisability of diatropic systems. No equivalent correlation is expected a priori for anti-aromatic paratropic systems, or clamped systems in which diatropic current is quenched by interaction with pi systems. Ab initio calculations of pi current density maps and dipole polarisability contributions confirm the expected correlation for monocycles, but show the limitations of polarisability as a measure of aromaticity. (C) 2003 Elsevier B.V. All rights reserved.