AB-INITIO STUDIES ON TETRAMETHYLUREA AND TETRAMETHYLTHIOUREA

Ab initio molecular orbital theory at the HF and MP2 levels was applied to study the structures of tetramethylurea and tetramethylthiourea and to carry out a conformational analysis of these molecules. The calculated structural parameters are in good agreement with the experimental observations and correctly describe the deviations of the molecular geometries from the planar structures. Conformational analysis shows that the rotational motions about the C-sp2-N bond are less hindered than the analogous motions in dimethylformamide and dimethylthioformamide. The methyl groups can rotate quite freely around the C-N bond in both the molecules studied here.