Influence of water on the infrared spectrum of crystalline N-methylacetamide

Infrared spectra of crystalline N-methylacetamide (NMA) at room temperature and near liquid helium temperature are reported for the pure vacuum distilled substance, and the same with defined amounts of water added. Several lines turn out to be highly water sensitive: those assigned to amide VI and IV, those at 804 and 1384 cm−1, and the one at 1413 cm−1 which is assigned to CH3(−N) sym. bend, the amide I and II bands, and two lines at 3103 and 3300 cm−1 mainly assigned to ν NH vibrations. It seems the spectra reported up to now have to be reconsidered cautiously concerning the water content of the samples and the assignments have to be thought through again.