RELATIONSHIP BETWEEN IR-C=O FREQUENCIES OF SEMICARBAZONES AND THEIR SOLID-STATE STRUCTURES

We have recently reported numerous abnormally high IR frequencies (up to 1760 cm−1) in the solid state for the carbonyl of semicarbazones (R1R2C=N-NH-CO-NH2) of a series of aldehydes and ketones (Kolb et al., J. Org. Chem., 54, 2431 (1989)). We are now proposing that these high frequencies are induced by an exceptionally strong vibrational coupling of the C=O in the centrosymmetric solid-state H-bonded structure. Raman spectroscopy was used in conjunction with IR to detect this vibrational coupling. Theoretical AM1 analysis for the exceptional strength of this coupling has been performed. © 1992, Taylor & Francis Group, LLC. All rights reserved.