Theoretical studies on stabilities, 13C and 3He NMR spectroscopy of C84O derived from C84 (D2d)

The equilibrium geometries and relative stabilities of the 19 possible isomers of C84O were studied using density functional theory (DFT) at B3LYP/6-31G level. The most stable geometry of C84O at the ground state has been found to be 8,9-C84O, where the oxygen atom is added to the 6/6 bond and an annulene-like structure is formed. Based on the optimized geometries at B3LYP/6-31G level, the 13C chemical shifts and nucleus independent chemical shifts (NICS) of the isomers for C84O were calculated at B3LYP/6-31G level. Compared with those of C84 (D2d), the chemical shifts of the bridged carbon atoms in 8,9-C84O are changed upfield. The isomers of C84O with the annulene-like structures are more aromatic than those with the epoxy structures. The dependence of the NICS values in 8,9-C84O on the distance of the helium atom from the cage center toward the hexagon or pentagon was also explored.