A Study of the Infrared Spectrum of the Amide Group

Abstract

The very strong 1560‐cm⁻¹ band of the N‐substituted amide group has been assigned previously either to ν(C–N) or to δ(N–H). This investigation consisted of a study of the frequency shifts of this and other bands in the infrared spectra of several N‐butyl‐ and N,N‐dibutyl‐ethanamides upon substitution of chlorine and fluorine in the 2 position. On the basis of these shifts and other properties of the band in question, observed in the spectra both of the pure compounds and of their CCl₄ solutions, it is concluded that the ν(C–N) assignment is correct. The apparent absence of the corresponding band from the spectrum of the N,N‐disubstituted amide group is explained by the accidental degeneracy of ν(C=O) and ν(C–N). Other bands were cataloged and assigned where possible.