Ab initio (6-31G*/ /3-21G) SCF calculations have been carried out on 15 isomers with the chemical formula C2SiH4• The isomers include structures with formal double and triple bonds to silicon, as well as carbenes and silylenes, so a direct comparison of these types of species is possible. The isomerization energies provide an opportunity to consider the relative strengths of analogous bonds to carbon and silicon. With the appropriate isodesmic reactions, the stabilizing or destabilizing effects of substituents and strain in three-membered rings both may be investigated.