Investigation of Tautomeric Structures of 6-Aza-2-Thiouracil-5-Carboxylic Acid Using Vibrational Spectroscopy Along With DFT Theoretical Method

Abstract

Molecular structure, tautomeric forms, vibrational modes, optic and electronic properties of 6-Aza-2-thiouracil-5-carboxylic acid (6A2T5CA) molecule were characterized by FT-IR, Raman, UV-VIS spectral methods and DFT method. The experimental results show that FT-IR and Raman spectroscopic methods could be used to determine the different tautomeric forms of 6A2T5CA molecule clearly. Although the title molecule has different tautomeric forms such as oxo and hydroxyl because of inter molecular interactions, it also has other tautomeric forms, due to intra molecular interaction of functional groups within the molecule. In particular, such structures change between each other depending on the solvent medium. Differences in some vibrational bands were observed in IR and Raman spectra. These differences were observed especially in N-H and O-H functional groups. In addition, vibrational modes, optimized structures, energy values, electronic transitions and HOMO-LUMO energy values of tautomeric forms were calculated using B3LYP/6-311G(2d,2p) level of theory. Experimentally obtained results were compared with theoretically obtained results and it was indicated that there was a good agreement with each other. It was also observed that the molecule has a different tautomeric form when it was dissolved in ethanol however, the molecule has another tautomeric form when it was dissolved in water.

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“…The peaks at 301, 362, 602, 1130, and 1460 cm −1 were assigned at vibrational modes of methyl groups [33]. The Au-S and N-H bonds share the Raman shift of CH 2 groups at 301 and 602 cm −1 , respectively [36,37]. The vibrational modes of C-N-H chains appeared at 813 and 990 cm −1 , whereas the vibrational modes of C-S bonds were assigned at the peaks at 640 and 728 cm −1 [33,38].…”