A simple model for counter-rotating ring currents in [n]circulenes

Ab initio current density maps for [7]circulene computed using the ipsocentric CTOCD-DZ/6-31G**//RHF/6-31G** method show that in both planar [3a (D-7h)] and non-planar, saddle-shaped [3b (C-2)] geometries this molecule sustains similar counter-rotating rim (diatropic) and hub (strongly paratropic) currents. A survey of the orbital contributions to the current density reveals that 3 like corannulene (1) is a 4d+4p system with just eight magnetically active and 20 magnetically inactive pi electrons. The graph-theoretical Huckel-London model describes the ring-current patterns of [n]circulenes in terms of a coupling strength (the ratio of radial and tangential resonance integrals) that charts the variation from the decoupled con-rotating currents of the [n]annulene-within-an-[m]annulene model to the fully coupled counter-rotating currents of the real [n]circulene. (C) 2002 Elsevier Science B.V. All rights reserved.