A ¹³C INADEQUATE and HF-GIAO Study of C₆₀H₂ and C₆₀H₆ Identification of Ring Currents in a 1,2-Dihydrofullerene

Abstract

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 (ϑp), but in these systems there is no strong correlation between ϑp 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