DFT, FT-Raman and FT-IR investigations of 5-methoxysalicylic acid

FT-IR and FT-Raman spectra of 5-methoxysalicylic acid (5MeOSA) have been experimentally reported in the region of 4000–10 cm−1 and 4000–50 cm−1, respectively. The optimized geometric parameters, conformational equilibria, normal mode frequencies and corresponding vibrational assignments of 5MeOSA (C8H8O4) are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-31++G(d,p) basis set. Furthermore, reliable vibrational assignments have made on the basis of potential energy distribution (PED) calculated and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 5MeOSA have been predicted. Calculations are employed for different conformations of 5MeOSA, both in gas phase and in solution. Solvent effects are investigated using chloroform and dimethylsulfoxide. All results indicate that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters, vibrational frequencies and assignments, IR and Raman intensities of 5MeOSA are solvent dependent.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► FT-IR, FT-Raman and quantum chemical calculations of 5MeOSA. ► The (d) isomer is supposed to be the most stable form of 5MeOSA. ► Conformational energy barrier is independent of the solvent. ► Vibrational frequencies and intensities change when going from nonpolar to polar solvents.