Infrared Spectra of Conjugated Amides: Reassignment of the C=0 and C=C Absorptions

Inspections of the infrared spectra of more than twenty tertiary 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^-1when a conjugation is introduced and that, among the plural absorptions at 1600—1700 cm^-1in 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.