Abstract Semi-empirical, ab initio Hartree—Fock, and density functional studies (including gradient corrections) on the structures and stabilities of C 60CH 2 are reported. Two low-energy isomers are found for both compounds which are roughly comparable in energy. These are obtained by bridging across the two different CC bonds in C 60. The interconversion pathway between the two isomers has been studied for C 60O. The corresponding energy barrier is large suggesting that it should be possible to isolate both isomers.