T. Mohamed, Ahmed E. Hassan, Ibrahim A. Shaaban
Feb 15, 2017
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Influential Citations
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Journal
Journal of Molecular Structure
Abstract
Abstract The infrared (4000–225 cm −1 ) and Raman (3500−60 cm −1 ) spectra of 2-Amino-5-(ethylthio)-1,3,4-thiadiazole (AEST; C 4 H 7 N 3 S 2 ) have been recorded in the solid phase. In addition, the 1 H and 13 C NMR spectra of AEST were obtained in DMSO- d 6 . We have focused on five staggered conformers ( 1–5 ) resulting from rotations of the methyl, ethyl and thioethyl groups around C C and C S bonds with the NH 2 group having a non-planar (sp 3 ) geometry. DFT-B3LYP/6-31G(d) calculations proved that only conformers 4 and 5 produce real vibrational frequencies and conformer 5 is the favored one with an energy difference of 124 cm −1 (0.35 kcal/mol) in agreement with the observed ethyl torsion at 92 cm −1 . The calculated frequencies, infrared intensities, Raman activities and potential energy distributions were compiled with spectral observations in favor of conformer 5 . All vibrational modes were assigned to their corresponding vibrational bands. Applying the observed methyl torsions, the kinetic parameter F number was found to be 5.3263 cm −1 and an average V 3 value of 1565 ± 14 cm −1 (4.48 ± 0.04 kcal/mol) was obtained. These values are close to the methyl barriers predicted from B3LYP/6-31G(d) potential surface scans. Moreover, the 1 H and 13 C NMR chemical shifts were also estimated for conformers 4 and 5 with DMSO as solvent implementing GIAO/PCM approximation utilizing B3LYP method at 6–311++G (d,p) basis set. The results are reported and discussed herein and compared with 2-Amino-5-ethyl-1,3,4-thiadiazole (AET) whenever appropriate.