The Computational Investigation of IR and UV-Vis Spectra of 2-isopropyl-5-methyl-1,4-benzoquinone Using DFT and HF Methods

Abstract

A theoretical study on the thymoquinone compound has been performed through two theoretical methods, DFT/B3LYP and HF with 6-31G, 6-31G(d, p) and 6-31++G(d, p) basis sets using Gaussian 09 program. Some theoretical properties, like vibrational and electronic properties especially UV-Vis and FT-IR spectra, of the title compound were analyzed and then compared with available experimental data. The calculated harmonic vibrational frequencies have been scaled with standard scaling factors 0.9 and 0.965 for HF and DFT/B3LYP, respectively and then compared with available experimental FT-IR spectrum. Furthermore, the statistical analysis was investigated to evaluate the performance of both the HF and DFT methods, including root mean square error (RMSE), mean absolute error (MAE) and mean percentage error (MPE). According to the assigned vibrational modes of the title compound, it could be concluded that the DFT/B3LYP method with 6-31++G(d, p) basis set had the best agreement with experimental data. UV-Vis absorption spectra, excitation energies, maximum absorption wavelength, electronic transitions and oscillator strengths of the title compound were calculated by time dependent density functional theory ( TD-DFT) method using the same basis set and compared with available experimental data. The results showed the best performer was HF method with 6-31G basis set.