Theoretıcal and experımental ınvestıgatıon of 2- hydroxyquinoxaline and 4-hydroxyquinazoline

Thesis Type: Doctorate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2010




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(d,p) density functional theory (DFT) method. The infrared and Raman spectra of 2-OHQ were recorded in the regions 400-4000 cm-1, and 50-3500 cm-1,wespectively. Vibrational wavenumbers were compared with IR, and Raman experimental data. Computational calculations at B3LYP/6-31+G(d,p), and 6-311G(d,p) 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 quadratic configuration interaction including single and double excitations (QCISD) method.Our calculations show that the keto form (Q1) of 2-OHQ was the most stable tautomer at B3LYP level using 6-311++G(d,p) basis set. All the tautomeric forms of 2-OHQ were determined and optimized. Bond distances, bond angles and dihedral angles were presented. For two most stable tautomers, the calculated wavenumbers were given. The tautomeric and conformational equilibrium geometry of 4- hydroxyquinazoline (4-HQ) have been studied using density functional theory (DFT) and Møller–Plesset second-order (MP2) methods in the gas phase and in water . The tautomerization processes in water (ε =78.54) were studied by using self-consistent reaction field theory (SCRF). Energetics and relative stabilities of the tautomers were compared and analyzed in both the gaseous and water. In agreement with experimental results, our calculations showed that the 4-HQ1 was the most stable form in the gas phase and in water . The harmonic wavenumbers of 4-HQ1 were calculated in the gas phase and in water by the B3LYP/ 6-311++G(d,p) DFT method and the wavenumbers were given. The infrared spectrum of 4-hydroxyquinazoline was recorded in the regions 400-4000 cm-1. The variation of dipole moments and charges on atoms is studied and natural (NBO) atomic charge was calculated in the gas phase and in water. In addition, two stable dimer forms of 4-hydroxyquinazoline calculated at the B3LYP/6-311++G(d,p) level in the gas phase and in water. In this study, the interaction energy effect of 2-OHQ and 4-HQ dimers has been examined.