Infrared Spectra of Conjugated Amides : Reassignment of the C=O and C=C Absorptions

Abstract

Inspections of the infrared spectra of more than twenty tertiaty and secondary amides and acid-induced shift experiments clarified that, in open chain amides, the carbonyl absorption shifts to lower frequency by 10-20 cm^-1 when a conjugation is introduced and that, among the plural absorptions at 1600-1700 cm^-1 in conjugated amides, the lowest absorption (usually the most intense one) should be attributable to the C=O and the higher absorptions are assignable to the C=C.