Structural and spectroscopic characterization of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid with experimental techniques and quantum chemical calculations

In this study, the molecular conformation, vibrational and electronic transition analysis of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid (C7H4F2O2) were presented using experimental techniques (FT-IR, FT-Raman and UV) and quantum chemical calculations. FT-IR and FT-Raman spectra in solid state were recorded in the region 4000–400 cm−1 and 4000–5 cm−1, respectively. The UV absorption spectra of the compounds that dissolved in ethanol were recorded in the range of 200–800 nm. The structural properties of the molecules in the ground state were calculated using density functional theory (DFT) and second order Møller–Plesset perturbation theory (MP2) employing 6-311++G(d,p) basis set. Optimized structure of compounds was interpreted and compared with the earlier reported experimental values. The scaled vibrational wavenumbers were compared with experimental results. The complete assignments were performed on the basis of the experimental data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. A study on the electronic properties, such as absorption wavelength, excitation energy, dipole moment and frontier molecular orbital energy, were performed by time dependent DFT (TD-DFT) approach. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands of steady compounds were discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The spectroscopic properties of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid were examined by FT-IR, FT-Raman and UV techniques and DFT/B3LYP method. ► The vibrational frequencies in the ground state are assigned and interpreted satisfactorily. ► The spectroscopic features of the dimer were investigated by DFT. ► The electronic properties, such as HOMO and LUMO energies, absorption wavelength and excitation energies, were performed by time-dependent DFT (TD-DFT) approach.