Endohedrally carbon doped C-60 systems, nC@C-60, with n = 1, 5, 10, 15 as well as [C@C-60](+2) and [5C@C-60](+2) forms have been subjected to AM I (RHF) type semiempirical quantum chemical analysis. The results indicate that they are stable but endothermic structures. The endohedral dopants have some influence on the molecular orbital properties of the cage and this effect gets more pronounced as the number of dopants increases. Calculated vibrational spectra are presented. (C) 2004 Elsevier B.V. All rights reserved.