Optimized geometry and vibrational spectra and NBO analysis of solid state 2,4,6-tri-fluorobenzoic acid hydrogen bonded dimer

Raman and IR spectra for 2,4,6-tri-fluorobenzoic acid have been recorded in the regions 50-4000 cm−1 and 400-4000 cm−1 respectively. Vibrational frequencies have been calculated by employing DFT method in dimeric form. SQM force field has also been used to calculate potential energy distributions in order to make conspicuous vibrational assignments. Raman activities calculated by DFT method have been converted to the corresponding Raman intensities using Raman scattering theory. Optimized geometries of the molecule have been interpreted and compared with the earlier reported experimental values for benzoic acid and some mono and di-fluorinated benzoic acids. Some of the vibrational frequencies of the title molecule are effected upon profusely with the fluorine substitutions in comparison to benzoic acid and these differences have been interpreted. The strong doubly hydrogen bonded interface of the dimerized system is well demonstrated by the red shift in O-H stretching frequency concomitant with the elongation of bond length.