Potential energy surfaces for rotation about the C(sp(2))-C(sp(3)) bond are reported for acetamide, propanamide, 2-methylpropanamide, and 2,2-dimethylpropanamide at different levels of ab initio electronic structure theory with correlation effects included. In all cases, fully optimized geometries of rotational minima are consistent with gas phase electron diffraction data and crystal structure data. The experimental barrier height for methyl rotation in acetamide is reproduced to within 0.1 kcal/mol. This study yields a set of improved criteria for the construction of rotational potentials for the C-a-C bond which are used to obtain improved MM3 torsional parameters. In addition, we find that the use of higher levels of theory leads to significantly different results than those obtained in prior Hartree-Fock studies on acetamide and 2-methylpropanamide.