The potential energy surfaces at different levels of ab initio electronic structure theory with correlation effects included are reported for rotation about the C(sp(2))-C(aryl) bond in N-methylbenzamide. The results reveal a minimum at a C=C-C=O dihedral angle of +/-28 degrees with barrier heights (MP2/aug-cc-pVTZ//BLYP/DZVP2/A2) of 0.48 kcal/mol at 0 degrees and 2.80 kcal/mol at 90 degrees. Fully optimized geometries are in good agreement with crystal structure data, and potential energy surfaces are consistent with the experimental dihedral angle distribution. The results are used to assign MM3 force field parameters to allow calculation on N-methylbenzamide and other benzamide derivatives.