A study of the molecular structure and spectroscopic properties of 3-hydroxy-2-quinoxalinecarboxylic acid by experimental methods and quantum chemical calculations

The mid-IR and Raman spectra of 3-hydroxy-2-quinoxalinecarboxylic acid (3HQC) were recorded. These spectra were interpreted with the help of B3LYP/6-311++G(d,p) calculations and potential energy distribution (PED) analysis. As a result of the calculations, seven tautomers were determined among many stable conformations. The experimental spectra were concordant with the theoretical data of two tautomers. In the functional group region overtone and combination bands were detected and assigned. In addition, because of several peaks in the IR spectrum, it was proposed that the 3HQC exhibits dimerization in condensed phase. Possible dimeric forms of 3HQC were evaluated at the same level of theory, and it has been seen that the calculation results confirm the above proposal. H-1 and C-13 NMR chemical shifts of 3HQC have been calculated, and compared with the experimental data. The frontier molecular orbital properties and the atomic charges were also theoretically obtained and presented. (C) 2012 Elsevier B.V. All rights reserved.