Substituent effect on C=O stetching vibrations in N-substituted 2-phenylacetamides

Abstract

The infrared spectra have been recorded for the N-substituted 2-phenylacetamides. The effect of substitutents on the spectral characteristics of the C=O group was investigated. When the electron-releasing substitutents are attached to the nitrogen atom, substituent effects are transmitted to the C=O group by the usual mechanism. However, the effect of electron-withdrawing substituents appears to be quite opposite, i.e., the carbonyl stretching vibrations are decreased. FT-IR data related to C=O stretchning frequencies are correlated with the sample Hammett equation Qx = σp + h and with the extended Hammett equation Qx = ασl + βσR + h. These correlations were interpreted in view of the transmission of electronic effects of the substitutents through the amide bond.