Aromaticity of C32 fullerene isomers and the 2(N+1)2 rule

Aromatic character of classical and non-classical fullerene isomers of C-32 was analyzed in terms of Hess-Schaad resonance energy (HSRE), topological resonance energy (TRE), bond resonance energy (BRE) and the 2(N+1)(2) rule of spherical aromaticity. According to the 2(N+1)(2) rule, C-32 fullerene isomers must be highly aromatic with a closed-shell electronic configuration. However, they are predicted to be antiaromatic with negative TREs, negative HSREs and large negative BREs. Two of the isomers have half-filled degenerate HOMOs, which is incompatible with the 2(N+1)(2) rule. Since they all are aromatized by acquiring two more electrons, it is obvious that the neutral C-32 species do not have a maximum degree of aromaticity. Thus, the aromaticity of a fullerene cage is strongly dependent on the connectivity of carbon atoms. (c) 2005 Elsevier B.V. All rights reserved.