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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