Aromaticity Survival in Hydrofullerenes: The Case of C 66 H 4 with Its π-Aromatic Circuits.

The isolated-pentagon rule (IPR) is a determining structural feature that accounts for hollow fullerene stabilization and properties related to C _n (n≥60) cages. The recent characterization of an unprecedented non-IPR hydrofullerene, C _2v C ₆₆ H ₄ , bearing two heptagons with adjacent fused-pentagon motifs, largely dismisses this feature. Herein, employing DFT calculations, the ¹³ C NMR spectroscopy and aromatic behavior of C _2v C ₆₆ H ₄ are explored. The results show the presence of three π-aromatic circuits at the bottom boat section of C ₆₆ H ₄ , indicating the unique features of this hydrofullerene in comparison to those of pristine C ₆₀ . In addition, under specific orientations of the external field, certain π-aromatic circuits are enabled, resulting in a more aromatic fullerene than that of C ₆₀ , but lower than that of the spherical aromatic C ₆₀ ^6- 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.
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