Theoretical NMR nJ(13C,13C) Scalar Couplings as Probes to Study Diamagnetic Ring Currents in Fullerenes

Abstract

In this work J(13C,13C) coupling constants and the principal components of nuclear magnetic shielding constants in the C60, C70, and Cð6KÞ 60 fullerenes are calculated at the B3LYP/cc-pCVDZ-sd level using optimized B3LYP/cc-pCVDZ geometries. Indirect spin–spin couplings are utilized to study local diamagnetic ring currents in fullerenes. In unsaturated carbon containing compounds, the Fermi contact (FC) contribution to long-range n J(13C,13C) (nO4) coupling constants is mainly transmitted through the mobile p-electronic system following a few simple rules: the alternating sign-rule and the pathway invariance. Besides, the absolute value of such a coupling decreases slowly when increasing the number of bonds separating the coupled nuclei. Without explicitly addressing the controversial topic of the aromaticity of fullerenes, we show that the p-transmitted components of the FC contribution provide information on factors affecting ring currents in fullerenes.