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 π 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 π systems. Ab initio calculations of π current density maps and dipole polarisability contributions confirm the expected correlation for monocycles, but show the limitations of polarisability as a measure of aromaticity.