Spherical aromaticity of Jahn-Teller active fullerene ions

Density functional theory was applied to compute the nucleus-independent chemical shifts of fullerene (C-60), the fullerene ion C-60 (10+), and the Jahn-Teller active fullerene anion C-60 (-) and cation C-60 (+). Positioning a He-3 nucleus inside the cage of each of these fullerene species facilitates investigations of the substantial differences among them, He-3 NMR chemical shifts can provide important data on the aromatic behavior of these molecular cages. Thus, we also calculated the NMR chemical shift of a He-3 atom positioned at the center of each fullerene species investigated (C-60, C-60 (10+), C-60 (-), and C-60 (+)). The data obtained revealed significant differences in the aromatic behavior of the C-60 (moderately aromatic) and C-60 (10+) (highly aromatic) species. The values of the nucleus-independent chemical shift parameters were also scanned along the intrinsic distortion path for the C-60 (-) and C-60 (+) species. In both cases, antiaromatic character decreases with increasing deviation from high-symmetry structures to low-symmetry global minimum points, resulting in the antiaromatic C-60 (-) and weakly aromatic C-60 (+).