Experimental and computational analysis (DFT method) of some quinoxalinones and benzoxazinones: spectroscopic investigation (FT-IR, FT-Raman, UV-Vis, NMR)

Abstract

© 2019, Indian Academy of Sciences. Abstract: The selected quinoxalinones and benzoxazinones derivatives, synthesized in our laboratory earlier, were explored by spectroscopic techniques (UV-Vis, IR, Raman and NMR) and theoretical study (DFT calculations). In order to understand the electronic properties of these compounds, the theoretical UV spectra have been investigated by TDDFT/B3LYP method with 6-311+G(d,p) basis set in ethanol as a solvent. For all compounds, the absorption of UV radiation with a wavelength around 415 nm with an oscillator strength f = 0.90 induces the intramolecular electronic transition (n→π*). The frontiers molecular orbitals are calculated, and contributions of the electronic transitions are determined. Also, we did quantum chemical calculations to investigate the corrosion inhibition properties of these molecules. The vibrational analysis was performed at the B3LYP/6-311+G(d,p) level of theory in vacuo. Obtained results are in very good agreement with experimental data. The calculated 13C NMR shifts in all cases are in good-to-excellent agreement. Also, 1H NMR predicted shifts are comparable with experimental results, but there are some deviations (for N–H shifts) probably as a consequence of intramolecular interactions. Graphic abstract: The previously synthesized quinoxalinones and benzoxazinones derivatives were explored by spectroscopic techniques (UV-Vis, IR, Raman and NMR) and theoretical study (DFT calculations). UV-Vis, IR, Raman and NMR spectra were calculated and compared with experimental data. The frontiers molecular orbitals are calculated, and contributions of the electronic transitions are determined. Besides that, we investigated the corrosion inhibition properties of these molecules using quantum chemical calculations. Compounds that contain electron donating groups (–OCH3, –NHCOCH3) exhibit better inhibitory efficiency than compounds that contain electron withdrawing groups (–NO2, alkenyl chain).[Figure not available: see fulltext.].