Ab initio computational study of selected C60H6 isomers

The relative energies of 18 isomers of C60H6 have been determined through geometry-optimized ab initio calculations. HF/6-31G∗ computations on the two lowest energy structures determined at the HF/3-21G level indicate that 1,2,4,11,15,30-C60H6 (18, with a C60Br6-like structure) lies only 0.4 kcal/mol higher in energy than 1,2,3,4,9,10-C60H6 (4). This remarkably close energy spacing was unexpected because, unlike in 4 in which addition occurs exclusively to 6,6 ring fusions, H2 addition in 18 occurs both 1,2 to a 6,6 ring fusion and 1,4 across 6-rings so as to place two double bonds into 6,5 ring fusions.