Aromaticity Survival in Hydrofullerenes: The Case of C66H4 with Its π-Aromatic Circuits

Abstract

The isolated-pentagon rule (IPR) is a determining structural feature that accounts for hollow fullerene stabilization and properties related to Cn (n≥60) cages. The recent characterization of an unprecedented non-IPR hydrofullerene, C2v C66H4, bearing two heptagons with adjacent fused-pentagon motifs, largely dismisses this feature. Herein, employing DFT calculations, the 13C NMR spectroscopy and aromatic behavior of C2v C66H4 are explored. The results show the presence of three π-aromatic circuits at the bottom boat section of C66H4, indicating the unique features of this hydrofullerene in comparison to those of pristine C60. In addition, under specific orientations of the external field, certain π-aromatic circuits are enabled, resulting in a more aromatic fullerene than that of C60, but lower than that of the spherical aromatic C606− fulleride. Notably, under a field aligned with the saturated carbon atoms, nonaromatic characteristics are exposed. This reveals that spherical-like cages can involve a complex magnetic response that heavily depends on the orientation of the applied field.