Chemical Physics Letters vol:405 issue:1-3 pages:136-141
Ipsocentric distributed-gauge calculations are used to map differential ring currents induced in [4n+2] and [4n] pi systems by simultaneous application of an axial magnetic and electric field (field gradient). In benzene, electric fields and gradients produce stratified first-order pi ring currents, opposing/reinforcing the intrinsic diatropic current, according to the height profile of charge depletion/enhancement induced by the electric perturbation. In (planarised) cyclooctatetraene, action of a uniform electric field is similarly rationalised, but response to the (totally symmetric) field gradient is dominated by a specific orbital effect, closing/widening of the small HOMO-LUMO gap leading to reinforcement/reduction of the intrinsic paratropic current. (c) 2005 Elsevier B.V. All rights reserved.