Computational study of urea and its homologue glycinamide: conformations, rotational barriers, and relative interactions with sodium chloride.

Conformational behaviors of urea and glycinamide have been investigated using the B3LYP functional with the 6-311+G* and 6-311+G** basis sets. Urea monomers have nonplanar minima at all the levels studied, even in the aqueous phase. In the case of glycinamide, the intramolecular hydrogen bond formed from the amide to the amine is important for stabilizing the global minimum. Bond rotations and nitrogen inversion barriers for glycinamide conformations have also been reported. The DFT calculated results suggest that urea conformers interact preferentially with the {111} surface of sodium chloride and such interactions can be responsible for the change in the habit of sodium chloride. Glycinamide conformers have a lower affinity toward the {111} surface of sodium chloride in water. The pyramidality of nitrogens in urea conformers does not influence the relative trends of interaction energies with sodium chloride surfaces. The mode of interactions predicted at the LDA/PWC/DND level for urea and glycinamide with sodium chloride for both slab and cluster models shows that the amide functionality (-CONH2) interacts with both Na(+) and Cl(-) ions on the {100} surface; however, the carbonyl oxygen of these additives predominantly interacts with the sodium ions on the {111} surface.