INVESTIGATION OF THE INFLUENCE OF THE SUBSTITUTE IN THE THIRD POSITION ON THE ELECTRONIC STRUCTURE OF 1,3-THIAZOLO[2,3-c][1,2,4]TRIAZOLE

Condensed 1,2,4-triazole derivatives exhibit a wide range of biological activity. In particular, triazolam, alprazolam and estazolam, which contain [1,2,4]triazolo[4,3-a][1,4]benzodiazepine system, are used as tranquilizers. Brotizolam is another tranquilizer, a derivative of thieno[3,2-f][1,2,4]triazolo [4,3-a][1,4]diazepine. The oral hypoglycemic drug sitagliptin contains the [1,2,4]triazolo[4,3-a]pyrazine system. In addition, pesticides such as flumetsulam, metosulam, cloransulam, diclosulam, florasulam, are derivatives of [1,2,4]triazolo[1,5-a]pyrimidine, [1,2,4]triazolo[1,5-c]pyrimidine and [1,2,4]triazolo[4,3-a]pyrimidine. Also, the search for anticancer drugs is based on the nucleus of 1,2,4-triazole. The popularity of the use of 1,2,4-triazole derivatives is primarily due to the high pharmacological action and relatively low toxicity of these compounds. The calculations were performed in the software package ORCA 4.2.1, by the method of density functional theory using the B3LYP/def2-TZVP method. After optimizing the geometry, to confirm the finding of the true local minimum, we calculated the matrix of the second derived energy from the coordinates of the atoms - in all cases, no imaginary frequencies were detected, indicating the finding of the true minimum. The magnetic characteristics of the compounds were calculated by the GIAO method. Using the method of density functional theory, the geometric and electronic structures of five compounds of the [1,3]thiazolo[2,3-c][1,2,4]triazole class were simulated, namely: unsubstituted [1,3]thiazolo[2,3-c][1,2,4]triazole, 3-methyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-ethyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-butyl-[1,3]thiazolo[2,3-c][1,2,4]triazole, 3-hexyl-[1,3]thiazolo[2,3-c][1,2,4]triazole. It is established that the length of the alkyl substituent in the third position has almost no effect on the shape and localization of the frontal molecular orbitals. In all cases, the isosurfaces are localized on the condensed system [1,3]thiazolo[2,3-c][1,2,4]triazole. The length of the alkyl substituent in the third position affects the ionization energy and electron affinity of [1,3]thiazolo[2,3-c][1,2,4]triazoles. Moreover, both the ionization energy and the electron affinity decrease with increasing alkyl chain length. The change in aromaticity with the change in the length of the alkyl substituent in the third position of the [1,3]thiazolo[2,3-c][1,2,4]triazole system is irregular, but the change is insignificant. It is established that both triazole and thiazole cycles are more aromatic than benzene, and the aromaticity of the triazole cycle is greater than thiazole. Keywords: 1,2,4-triazole; 1,3-thiazole, thiazolo[2,3-c][1,2,4]triazole, frontal molecular orbitals; aromaticity.