The experimental and theoretical investigation methods of the structure of 5-fluoro-salicylic acid and 5-chloro-salicylic acid molecules by spectroscophic

In this study, the experimental and theoretical study on the structures and vibrations of 5-Fluoro-salicylic acid and 5-Chloro-salicylic acid (5-FSA and 5ClSA, C7H5FO3 and C7H5ClO3) are presented. The Fourier Transform infrared spectra (4000?400 cm?1) and the Fourier Transform Raman spectra (4000?50 cm?1) of the title molecules in the solid phase have been recorded for each one. 5-FSA and 5-ClSA the geometrical parameters and energies have been obtained for all eight conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. There are eight conformers, Cn, n=1-8 for this molecule each one. The computational results identify the most stable conformer of 5-FSA and 5ClSA as the C1 form. The vibrations of stable and unstable conformers of 5-FSA and 5ClSA are researched with the aid of quantum chemical calculations. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The molecular structures, vibrational frequencies, infrared intensities and Raman scattering activities were calculated a pair of molecules linked by the intermolecular O?H?.O hydrogen bond. The spectroscopic and theoretical results are compared to the corresponding properties for 5-FSA and 5ClSA monomers and dimer of C1 conformer. The optimized bond lengths, bond angles and calculated frequencies showed the best agreement with the experimental results.