FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular geometry of 2-hydroxyquinoxaline

With the purpose of finding predominant tautomer among seven possible isomers of 2-hydroxyquinoxaline 2-OHQ, its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-311++G∗∗ DFT method. The infrared and Raman spectra of 2-OHQ were recorded in the regions 400–4000 cm−1, and 50–3500 cm−1, respectively. Vibrational wavenumbers were compared with IR, and Ra experimental data. Computational calculations at B3LYP/6-31+G∗∗, and 6-311G∗∗ levels were also employed in the study of the predominant tautomeric form of 2-OHQ. To support our relative energy results we also used the QCISD method. In agreement with experimental results, our calculations show that the keto form of 2-OHQ is the most stable tautomer and the best results were obtained at B3LYP level using 6-311++G∗∗ basis set. All the tautomeric forms of 2-OHQ were determined and optimized. Bond distances, bond angles and dihedral angles are presented. For two most stable tautomers, the calculated wavenumbers were given. In addition, two stable dimer forms of 2-hydroxyquinoxaline calculated at the B3LYP/6-31G∗ level. The dimer A is by 15.57 kcal mol−1 more stable than dimer B.