ABINITIO VIBRATIONAL ANALYSIS OF HYDROGEN-BONDED TRANS-N-METHYLACETAMIDE AND CIS-N-METHYLACETAMIDE

In order to characterize the vibrational dynamics of the hydrogen-bonded N-methylacetamide (NMA) molecule, we have calculated the energies, geometries, and force constants (at the 4-31G* level) of trans-NMA and cis-NMA to which are hydrogen bonded two H2O molecules, one at the NH group and one at the CO group. The force constants for trans-NMA were scaled to experimental frequencies for NMA in aqueous solution and resulted in predicted frequencies within 5 cm-1 of observed bands. Experimental data for cis-NMA are more limited, but transfer of scale factors from the isolated molecule permitted verification of the assignments of two resonance Raman bands proposed to be characteristic of this isomer.