Asian Journal of Physics Vol 26, Nos 11 & 12 (2017) 365-373

Molecular structure and vibrational spectra of 2-thiouracil: A comparison with uracil

Kaushal Rani1,2, Jay Prakash3, S P Singh4, J K Vats5, M A Palafox6 and V K Rastogi1
1Indian Spectroscopy Society, KC-68/1, Old Kavinagar, Ghaziabad-201 002, India
2Department of Physics, Meerut College, Meerut-250 003, India
3Department of Physics, Kamla Nehru P.G. College, Tej Gaon, Raebareli-229 215, India
4Department of Physics, Dr B R Ambedkar Govt Degree College, Mainpuri-205 263, India
5P G Department of Physics, Jai Prakash University, Chapra-841 301, India
6Departamento de Química-Física, Facultad de C Químicas, Universidad Complutense, Madrid-28040, Spain

Spectroscopic and structural studies of uracil and its derivatives have been reported both theoretically and as well experimentally by many authors. Uracil and its thio analogue 2-thiouracil (2-TU) affect the growth of plants. To understand biochemically the mode of inhibitory or malforming actions of uracil and 2-TU on the growth of rice and wheat plants, the knowledge of their structures is essential. Hence, in the present work an attempt has been made to study their spectra and structures using vibrational spectroscopy as technique. The replacement of an oxygen atom by sulphur leads to a shift of the experimental ν(N-H) bands to lower wavenumbers, 27 cm–1 for the N1-H mode and 20 cm–1 for N3-H. The effect of sulphur substitution on ν(N3-H) wavenumber and intensity reflects changes in proton abilities of this group as well as the hydrogen bonding in which they participate. Compared to uracil, the sulfur atom in 2-TU results mainly in a significant change of the bond-length at the substitution site: S=C ~1.66 Å, as compared to C=O ~1.22 Å. This fact leads to a slightly reduction in the neighboring bond lengths N1-C2 and N3-C2, but the N-H and C-H bonds are little affected. © Anita Publications. All rights reserved.
Keywords: Uracil, 2-Thiouracil, FT-IR, FT-Raman, Density Functional Theory (DFT).

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