Spectra of Homologous Series of Monosubstituted Amides

Abstract

Infrared spectra of the pure liquid and of dilute solution were observed for N‐methyl, N‐ethyl, N‐propyl, and N‐butyl acetamides and propionamides and of N‐deuterated N‐butylacetamide. Also infrared spectra of N15‐butylacetamide and N‐deuterated N15‐butylacetamide and the Raman spectra of N‐butylacetamide and N‐deuterated N‐butylacetamide were observed. In each series a band in the higher members was related to each band of the N‐methyl compound on the basis of similarity in frequency, intensity, band width, and the influence of dilution. In N‐methylacetamide and N‐butylacetamide bands thus related were found to have also similar Raman activities and similar shifts on replacing the peptide hydrogen by deuterium. The extra bands could be related systematically to the extra CH2 groups. The implications of these results in protein spectroscopy and in the spectroscopic study of homologous series is discussed.