A Study of the Infrared Spectrum of the Amide Group

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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.