Ring-current assessment of the Annulene-Within-an-Annulene model for some large coupled super-ring conjugated-systems

Abstract

The Annulene-Within-an-Annulene (AWA) model for conjugated super-ring systems, proposed by Barth and Lawton nearly fifty years ago, is further tested on six newly considered 'coupled' structures by means of π-electron ring-currents and bond-currents calculated via the Hückel-London-Pople-McWeeny (HLPM) formalism. Super-ring systems are said to be decoupled when the bonds connecting the central ring to the outer perimeter never appear as anything other than single bonds in any Kekulé structure that can be devised for the system as a whole. The preliminary conclusions of other recent investigations - by the same HLPM method and by ipso-centric ab-initio approaches - are verified. Phenylene-[5]-circulene, a (coupled) alternant isomer of the much-studied (decoupled) non-alternant system [10,5]-coronene, is also considered. It is advised that the AWA model should in future either be used with considerable caution in very specific circumstances, or it should be abandoned altogether.