Accurate calculation, prediction, and assignment of He-3 NMR chemical shifts of helium-3-encapsulated fullerenes and fullerene derivatives

Helium-3 NMR chemical shifts of various He-3-encapsulated fullerenes (He-3@C-n) and their derivatives have been calculated at the GIAO-B3LYP/3-21G and GIAO-HF/3-21G levels with AM1 and PM3 optimized structures. A good linear relationship between the computed He-3 NMR chemical shifts and the experimental data has been determined. Comparisons of the calculation methods of He-3 NMR chemical shifts show that GIAO-B3LYP/3-21G with AM1-optimized structures yields the best results. The corrected He-3 NMR chemical shifts were calculated from the correction equation that is obtained through linear regression fitting of the experimental and calculated He-3 NMR chemical shifts over a wide range of(3)He-encapsulated fullerene compounds. The corrected He-3 NMR chemical shifts match the experimental data very well. The current computational method can serve as a prediction tool and can be applied to the assignments and reassignments of the He-3 NMR chemical shifts of He-3@C-n and their derivatives