The characteristic band of secondary amides at 3100 cm−1

Abstract The characteristic band of secondary amides at 3100 cm−1 was explained to be due to the Fermi resonance of the NH stretching vibration with the overtone of the amide II vibration for the trans configuration and with the combination of the CO stretching and NH in-plane bending vibrations for the cis configuration. The NH stretching frequencies of secondary amides should be corrected for the Fermi resonance before they are correlated with the strengths of hydrogen bonds.