Synthesis of 1-aroyl-3-methylsulfanyl-5-amino-1,2,4-triazoles and their analysis by spectroscopy, X-ray crystallography and theoretical calculations

N-Aroyl-1,2,4-triazoles TAM and TACl were regioselectively synthesized in excellent yields through an efficient N-acylation reaction of 3-amino-5-methylsulfanyl-1H-1,2,4-triazole with aroyl chlorides. Structures of N-aroyl-1,2,4-triazoles were studied by single-crystal X-ray diffraction, observing that their crystal structures are characterized by the formation of dimers through N-H center dot center dot center dot N bonds. The supramolecular assembly depends on the sort of connections between dimers, which notably change with the parasubstituent on the aroyl group. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (chi), electrophilicity index (omega), hardness (eta), and chemical potential (mu) are correlated with the HOMO and LUMO orbital energies. Moreover, molecular electrostatic potential maps of both molecules have been calculated showing a negative region at N2 atom of the 1,2,4-triazole ring instead of exocyclic amino group. The vibrational spectral analysis was carried out using infrared spectroscopy in the range 4000-400 cm(-1) for N-aroyl-1,2,4-triazoles TAM and TACl. The experimental spectra were recorded in the solid state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-31G(d,p) method and basis set yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared spectra utilizing the results of these calculations led to an excellent overall agreement with the observed spectral patterns. (C) 2020 Published by Elsevier B.V.