Integrated absorption intensities of the carbonyl band in amides and anilides

Abstract

The integrated absorption intensities of the carbonyl band of secondary and tertiary amides of formamide, acetamide, and propionamide series have been determined. These values vary from 2.5 to 5.7 units of intensity. The high values of the integrated intensities of the carbonyl band in amides are attributed to the high polarity of the C=O group due to the considerable contribution of the dipolar resonance structure to the ground state in these molecules or to the mixing of the π -orbital of the C=O group and 2 P z orbitals of the nitrogen atom. The integrated intensities of the carbonyl band of N -methyl and N,N -dimethyl amides are higher than those of the corresponding N -phenyl and N,N -diphenyl amides. Similarly, the integrated intensities of the same band in N,N -dimethyl and N,N -diphenyl amides are higher than those of the corresponding N -methyl and N -phenyl amides, respectively. These changes in the intensities are accounted for as due to the variation in the interaction of the π and the p orbitals.