The photochemical reactions of [60]fullerene with various aromatic aldehydes or ketones 1a−ncarrying an alkyl group at the ortho position were examined. Some of them afforded stableo-quinodimethane adducts 2 with a hydroxy group attached to the cyclohexene ring. The adducts2 were found to adopt one or both of two conformers A and E, which possess pseudoaxial andpseudoequatorial hydroxy groups, respectively. The conformer ratios depended remarkably on thesubstituents attached to the aromatic nucleus and the cyclohexene ring. The dynamic behavior of2 was also investigated by the VT-NMR technique.