Study of electron densities of methyl acetate, N-methylacetamide and N,N'-dimethylurea by quantum mechanical investigations .1. Gas phase

The conformations and electron densities of a simple ester, amide and urea derivative have been studied with quantum mechanical methods at the Becke3LYP/6-31 + G* level. Discussions of electron densities use Natural Atomic (NAG) and Natural Bond Orbitals (NBO). The gas phase calculations indicate the importance of overall resonance stabilization for all molecules studied. It decreases in the series urea > amide > ester. The delocalization of one nitrogen lone pair into the pi(c=o)(*), bond is lower in the urea compared with the amide. This property is associated with a high flexibility of ureas.