Vibrational spectrum, force Field calculations, thermodynamic functions and barrier to internal rotation for benzoyl fluoride

Abstract

The i.r. and Raman spectra of benzoyl fluoride have been studied in solid, liquid and vapour phases. All of the 36 normal modes of vibration have been assigned in the light of normal coordinate analysis. The carbonyl group stretching mode exhibits a broad band group at ∼ 1800 cm-1, with three bands of comparable intensities. The appearance of the triplet is explained by the existence of strong Fermi resonance. The CO stretch, CF stretch and CFO wag modes have been confidently assigned at 1810, 1014 and 682 cm-1 (in solid/liquid state spectra), respectively. The former two of these show an upward shift and the latter one shows a downward shift in going from solid phase to vapour phase. These results evidence the presence of strong intermolecular interactions in solid and liquid phases. Thermodynamic functions and barrier to internal rotation of the CFO group have also been computed using the fundamental frequencies. The barrier height is found to be ∼4.91 kCal/mole. © 1987.