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

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 ->*). 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 C-13 NMR shifts in all cases are in good-to-excellent agreement. Also, H-1 NMR predicted shifts are comparable with experimental results, but there are some deviations (for N-H shifts) probably as a consequence of intramolecular interactions.