Aromaticity of C 32 fullerene isomers and the 2( N+1) 2 rule

Abstract

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.