Ab Initio and Molecular Mechanics Calculations of Various Substituted Ureas - Rotational Barriers and a New Parametrization for Ureas

High-level ab initio calculations have been performed on urea, methylurea, tetramethylurea and three isomers of dimethylurea to obtain accurate rotational barriers. Results of MP2(fc)/6-31 G(d) calculations are compared to those with lower basis sets and semiempirical calculations. The MM2(87) force field has been parameterized.