RELATIVE STABILITIES OF 6 6 AND 5/6 C-60(CH2)(3)/

Bridging with the -(CH2)(3)- group over a bond in C-60 introduces a ne w five-membered ring and allows for three isomers. One originates in t he 6/6 bond bridging, the other two in the 5/6 bridging with the centr al CH2 group located more above the related pentagon (5/6(5)) or hexag on (5/6(6)). According to the AM1 semi-empirical quantum-chemical calc ulations the ground state of the system is represented by the 6/6 stru cture, located 76 and 78 kJ/mol below the 5/6(5) and 5/6(6) species, r espectively. A similar picture is produced by the MNDO, PM3 and SAM1 c omputations. The bridged bond remains as a relatively long single bond in the all three isomers (1.577, 1.621, 1.621 Angstrom). IR spectra a re also computed, and effects of temperature on the thermodynamic rela tive stabilities evaluated. The 6/6 species remains the dominant compo nent of the equilibrium isomeric mixture even at high temperatures.