Vibration
Assignment, B3pw91 Calculation and Conformational Analysis of Antimicrobial
5-Amino -3-(Methylthio)-1-(1,3,4-Thiadiazol -2-Yl)-1H-Pyrazole-4-Carbonitrile.
In this study, we
conducted infrared spectroscopy measurements on solid
5-amino-3-(methylthio)-1-(1,3,4-thiadiazol-2-yl)-1H-pyrazole-4-carbonitrile
(AMTDPC, C7H6N6S2). The spectra
were obtained at a resolution of 4 cm?1 and 0.5 cm-1,
within the spectrum region of 4000–200 cm-1. Furthermore, the
observation of NMR spectra for 1H and 13C has been
documented. Nine rotational isomerisms, consisting of nine Cs and one C1
symmetry, are postulated for the AMTDPC molecule due to internal rotation
occurring around C–N and/or C–S bonds. The isomers are finally characterized by
two conformers (1-2) with energies below 1000 cm-1, as determined
through quantum mechanical calculations utilizing RHF and DFT/B3PW91. Based on
forecasts, conformer 1, which is the rotamer with the lowest energy and
produces real frequencies, is expected to have a stability order of 1 > 2.
The spectrum modeling provides complete support for Conformer 1, making it the
preferred option based on the recorded infrared (IR), 1H, and 13C
spectral data. The chemical shifts at the B3PW91/6-31G level were successfully
determined using the Polarizable Continuum Model (PCM) and the Gauge-Invariant
Atomic Orbitals (GIAO) technique, regardless of the presence or absence of the
solvent. The results of the NMR studies provided indications of both
constrained and unconstrained internal rotation of NH2 around C-N
bonds. In order to propose a comprehensive and reliable vibrational assignment
for each of the foundations of AMTDPC, potential energy distributions and
normal coordinate analysis have been employed. Additionally, supplementary
investigations were carried out to examine the torsional obstacles encountered
during the internal rotation of the NH2, CH3, CH3S,
and thiadiazole ring. Based on spectrum measurements that exhibited a high
level of concurrence with the anticipated values, it may be concluded that
conformer 1 emerged as the isomer with the highest stability. Also there are small differences between the
calculated bond distances and the x-ray readings for comprised compounds.
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