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

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2013-01, Vol.101, p.14-21
• Main Authors: Badoğlu, Serdar, Yurdakul, Şenay
• Format: Article
• Language: English
• Subjects: 3-Hydroxy-2-quinoxalinecarboxylic acid; Conformers; DFT; Tautomerism; Vibrational spectroscopy
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2012.09.080

[Display omitted] ► Vibrational spectra, NMR and NBO analysis on 3-hydroxy-2-quinoxalinecarboxylic acid were reported. ► DFT calculated data such as IR and NMR were consistent with the experimental data. ► The structural, geometric, and electronic parameters were discussed based on the DFT calculations. ► The IR spectrum and NMR shifts suggested the presence of two tautomers and a dimer in the sample. 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. 1H and 13C 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.