Amide bands in the IR spectra of urethanes

The objective of this article is investigation of the normal modes of vibrations of molecules containing amide or urethane groups. Comparison between methyl-N-methylcarbamate (MMC) and N-methylacetamide (NMA) has been discussed. Density functional (DFT) calculations at B3LYP/6-31G(d) level have been employed to investigate the normal modes of MMC and several simple urethanes. This level was used as a compromise between accuracy and applicability to larger systems. The obtained results are in good agreement with experimental spectra. Finally, we have confirmed that the use of “amide terminology” is correct when addressing urethane molecules.