A (13)C INADEQUATE and HF-GIAO study of C(60)H(2) and C(60)H(6) identification of ring currents in a 1,2-dihydrofullerene

The hydrofullerenes C(60)H(2) (1) and C(60)H(6) (2) have been prepared in (13)C-enriched form and 2D INADEQUATE NMR spectra were measured. These spectra have provided unambiguous (13)C assignments for 2, and nearly unambiguous assignments for 1. In both cases, the most downfield resonances are immediately adjacent to the sp(3) carbons, despite the fact that these carbons are the least pyramidalized carbons in the molecule. Typically, (13)C chemical shifts move downfield with increasing pyramidalization (THETA(p)), but in these systems there is no strong correlation between THETA(p) and delta. HF-GIAO calculations are able to predict the chemical shifts, but provide little chemical insight into the origin of these chemical shifts. London theory reveals a significant paramagnetic ring current in 1, a feature that helps explain the (1)H shifts in these compounds and may contribute to the (13)C chemical shifts as well.