TY - JOUR
T1 - Raman, infrared and NMR spectral analysis, normal coordinate analysis and theoretical calculations of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione and its thiol tautomer
AU - Mohamed, Tarek A.
AU - Soliman, Usama A.
AU - Shaaban, Ibrahim A.
AU - Zoghaib, Wajdi M.
AU - Wilson, Lee D.
N1 - Publisher Copyright:
© 2015 Elsevier B.V. All rights reserved.
PY - 2015
Y1 - 2015
N2 - Raman (3400-100 cm 1) and infrared (4000-200 cm 1) spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3 H)-thione (C3H4N2S3; MTT) were measured in the solid state, and the 1H/13C NMR spectra were obtained in DMSO-d6. Initially, twelve structures were proposed as a result of thiol-thione tautomerism and the internal rotation about the C-S bonds. The energies and vibrational frequencies of the optimized structures were calculated using the 6-31G(d) basis set with the methods of MP2 and DFT/B3LYP with Gaussian 98 quantum calculations. Additionally, 1H/13C NMR chemical shifts were predicted for the thiol (structure 5) and thione (structure 9) tautomers by means of B3LYP/6-311+G(d, p) calculations utilizing the GIAO approximation and the PCM solvation model. After complete relaxation of twelve candidate isomers, the thione tautomer (structure 9) was favored owing to its low energy and its predicted real spectral frequencies. These results agree with the recorded infrared and Raman results, in addition to the observed/calculated 1H and 13C NMR spectra. Aided by normal coordinate analysis and potential energy distributions (PEDs), complete vibrational assignments have been proposed for all observed fundamentals for the thione tautomer. With the aid of MP2/6-31G(d) potential surface scans, CH3, CH3S, and SH barriers to internal rotations were estimated with the optimized structural parameters from the MP2 method with the 6-31G(d) basis set. The results are discussed herein and compared with similar model compounds whenever appropriate.
AB - Raman (3400-100 cm 1) and infrared (4000-200 cm 1) spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3 H)-thione (C3H4N2S3; MTT) were measured in the solid state, and the 1H/13C NMR spectra were obtained in DMSO-d6. Initially, twelve structures were proposed as a result of thiol-thione tautomerism and the internal rotation about the C-S bonds. The energies and vibrational frequencies of the optimized structures were calculated using the 6-31G(d) basis set with the methods of MP2 and DFT/B3LYP with Gaussian 98 quantum calculations. Additionally, 1H/13C NMR chemical shifts were predicted for the thiol (structure 5) and thione (structure 9) tautomers by means of B3LYP/6-311+G(d, p) calculations utilizing the GIAO approximation and the PCM solvation model. After complete relaxation of twelve candidate isomers, the thione tautomer (structure 9) was favored owing to its low energy and its predicted real spectral frequencies. These results agree with the recorded infrared and Raman results, in addition to the observed/calculated 1H and 13C NMR spectra. Aided by normal coordinate analysis and potential energy distributions (PEDs), complete vibrational assignments have been proposed for all observed fundamentals for the thione tautomer. With the aid of MP2/6-31G(d) potential surface scans, CH3, CH3S, and SH barriers to internal rotations were estimated with the optimized structural parameters from the MP2 method with the 6-31G(d) basis set. The results are discussed herein and compared with similar model compounds whenever appropriate.
KW - Infrared
KW - Internal rotation barrier
KW - MP2 and DFT calculations
KW - Raman
KW - Vibrational assignment
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U2 - 10.1016/j.saa.2015.05.039
DO - 10.1016/j.saa.2015.05.039
M3 - Article
C2 - 26056985
AN - SCOPUS:84934984545
SN - 1386-1425
VL - 150
SP - 339
EP - 349
JO - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
JF - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
IS - 1
ER -