The internal rotation barriers of methylsilane, methyl mercaptan, methylphosphine, and disilane are calculated with and without complete geometry optimization in three different CNDO parametrizations. It is found that Santry's recent reparametrization is most reliable for both geometries and barriers and that geminal and bonded interference interactions are more important than those between vicinal atoms for these molecules. None of the parametrizations give reasonable dipole moments.