Theoretical study on molecular structure and vibrational analysis included FT-IR, FT-Raman and UV techniques of 2,4,5-trimethylbenzoic acid (monomer and dimer structures)

•Monomeric conformations of 2,4,5-trimethylbenzoic acid were investigated.•The compound was characterized by FT-IR and FT-Raman, and UV spectroscopy.•The vibrational frequencies and electronic absorption wavelengths were calculated by DFT method.

Theoretical study on the structural and vibrational analysis of monomer and dimer structures of 2,4,5-trimethylbenzoic acid (2,4,5-TMBA, C10H12O2) were presented. The geometry of the molecule was fully optimized. The Fourier transform infrared (FT-IR) and the Fourier transform Raman (FT-Raman) spectra of the title molecule in solid phase were recorded in the region 4000–400 cm−1 and 4000–50 cm−1, respectively. The geometrical parameters and energies were investigated with the help of Density Functional Theory (DFT) employing B3LYP method and 6-311++G(d,p) basis set. The spectroscopic data of the molecule in the ground state were calculated by using DFT/B3LYP method with the 6-311++G(d,p) basis set. The vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes. The geometric parameters were compared with experimental data of the title molecule. The UV absorption spectrum of the studied compound was computed and recorded in the range of 190–400 nm dissolved in water and ethanol. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and presented. In addition these, thermodynamic properties and Mulliken atomic charges were performed.

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