STUDY OF ELECTRON-DENSITIES OF METHYL ACETATE, N-METHYLACETAMIDE AND N,N'-DIMETHYLUREA BY QUANTUM-MECHANICAL INVESTIGATIONS .2. SOLVENT MODELS

The electron densities of a simple ester, amide and urea derivative ha ve been studied with quantum mechanical methods at the Becke3LYP/6-31 + G level. Solvent effects were modelled with an SCRF approach based on the SCI-PCM electrostatic continuum solvation model and with explic it inclusion of water molecules at different hydrogen bond donor-accep tor sites of the solutes. Discussions of electron densities use Natura l Atomic (NAG) and Natural Bond Orbitals (NBO). Electrostatic interact ions with a polar solvent yield polarization of the pi(C=0) bond towar ds oxygen, a higher delocalization of lone pairs from -O- or -NH- into the pi(C=0) anti-bond and a higher localization of lone-pairs at the carbonyl oxygen. Particular different changes in charge densities aft er explicit hydration of the molecules are discussed.