Ab initio studies on geometry and vibrational spectra of N-methyl formamide and N-methylacetamide

The molecular conformation, ground state molecular vibrations and force field of N-methylformamide (NMF) and N-methylacetamide (NMA) have been studied by the ab initio method at the Hartree–Fock level using the $6-31+g^*$ basis set. The potential energy surface of NMA is investigated by the ab initio method with full geometry optimization. For both the molecules, trans conformer was found to be the most stable. For trans-NMF, methyl group in the staggered conformation and for trans-NMA, methyl groups in cis–trans position with respect to –CONH– group represent global minima. The vibrational spectral analysis has been carried out for both NMF and NMA. Comparisons with the previous assignments for amide bands have been made. The present results are compared with the previous results of structure and vibrational spectra and discussed