CONFORMERS OF TRANS-N-METHYLACETAMIDE - ABINITIO STUDY OF GEOMETRIES AND VIBRATIONAL-SPECTRA

Energies and geometries have been obtained, at the 4-31G* level, for the four stable conformers of trans-N-methylacetamide that result from conformational isomerism of the CH3 groups. Ab initio force fields were obtained for these four structures, and the force constants were scaled to experimental matrix-isolated frequencies. The results show that the conformers should be spectroscopically distinguishable, and in fact the observed bands can be satisfactorily assigned on this basis without invoking a non-planar amide group. Conformational isomerism may also be partly responsible for the unusual breadth of the amide V band.