Vibrational Spectroscopy of <i>N</i>-Methylacetamide Revisited

Abstract

Although a lot of work has been performed on the vibrational analysis of N-methylacetamide (NMA), some uncertainties and even contradictions remain, mainly due to the fact that the structure of NMA at room temperature is not stable due to traces of water or due to the fact that the authors only studied the infrared or the Raman spectra. On the basis of the infrared and Raman spectra in the −196 °C to +100 °C temperature range, we have shown that the effects of temperature on the structure and the changes in the strength of the hydrogen bonding within a structure elucidate a lot of the complexity of the solid state vibrational spectra of NMA. Force field calculations on the monomer and multimers (n = 6) and solution spectra of NMA and the N-deuterated compound are used to provide a better understanding of the influence of hydrogen bonding on the typical amide fundamentals. Nine typical so-called “amide bands” have been further characterized.