Vibrational Assignment of Benzil and Its ¹⁸O Substituted Derivative

Abstract

Vibrational spectra of benzil and benzil-¹⁸O in the solid phase and in the melt as well as in solution have been measured in the Raman (4000–20 cm⁻¹) and the infrared (4000–100 cm⁻¹). Their differential infrared linear dichroic spectra of oriented polycrystalline layers (4000–200 cm⁻¹) have been also recorded and studied. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes. The presence of syn- and anti-phase vibrations of both phenyl rings is rediscussed. The previous assidnments of the in-plane and out-of-plane deformation of the carbonyl group and some fundamentals of bicarbonyl moiety are questioned and corrected.

Key Words:

• IR spectra
• Raman spectra
• isotope labelling
• benzil
• benzil-¹⁸O
• vibrational assignment