Studies of equilibrium geometries and electronic spectra for C78O4

Equilibrium geometries and relative stabilities of 24 possible isomers for C78O4 based on C-78 (C-2v) were studied by intermediate neglect of differential overlap (INDO) calculations. It was indicated that the most stable geometry is 28,29,30,31,52,53,73,78-C78O4, where three oxygen atoms are added to the same hexagon, through which the longest axis of C-78 (C-2v) goes, and the forth oxygen atom is added to the C(73)-C(78) bond intersected by the shortest axis of C-78 (C-2v), and epoxide structures are formed. Electronic spectra of C78O4 isomers were investigated based on the optimized geometries. The blue shift of the first absorption for 28,29,30,31,52,53,73,78-C78O4 compared with that of C-78 (C-2v) was rationalized and nature of transition for the peaks discussed. (C) 2005 Wiley Periodicals, Inc.