A ¹³C INADEQUATE and HF-GIAO study of C₆₀H₂ and C₆₀H₆ identification of ring currents in a 1,2-dihydrofullerene

The hydrofullerenes C₆₀H₂ (1) and C₆₀H₆ (2) have been prepared in ¹³C-enriched form and 2D INADEQUATE NMR spectra were measured. These spectra have provided unambiguous ¹³C assignments for 2, and nearly unambiguous assignments for 1. In both cases, the most downfield resonances are immediately adjacent to the sp³ carbons, despite the fact that these carbons are the least pyramidalized carbons in the molecule. Typically, ¹³C chemical shifts move downfield with increasing pyramidalization (Θ_p), but in these systems there is no strong correlation between Θ_p and δ. 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 ¹H shifts in these compounds and may contribute to the ¹³C chemical shifts as well.