Endohedral chemical shifts in higher fullerenes with 72-86 carbon atoms

For all isolated pentagon isomers of the fullerenes C-60-C-86 with nonzero HOMO-LUMO gap and for one nonclassical C-72 isomer (C-2v), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental He-3 NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C-60, C-70 and C-76). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental He-3 chemical shifts, the assignments of the observed He-3 NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C-82 and one C-86 isomer (C-82:3 and C-86:17). The calculated helium chemical shifts also suggest the reassignment of the delta(He-3) resonances of two C-78 isomers.