Теоретичне дослідження впливу аміно- та меркапто-груп ароматичність ядра 1,2,4-тризолу

Abstract

The work is devoted to the theoretical study of the effect of the introduction of mercapto and amino groups on the aromaticity of 1,2,4-triazole cycle. Aromaticity is one of the key concepts in modern organic chemistry, and the question of the aromaticity study of various heterocyclic systems (pyrazolopyridazinones, fullerenes, polycyclic boropins) is an urgent task that is being explored by multiple scientific groups. The scientific area of our team is mainly devoted to the study of the synthesis and properties of both neutral and charged poly-substituted symmetric triazole derivatives. It was decided to quantify the aromatic characteristics of amino- and mercapto-substituted 1,2,4-triazoles, to compare their aromaticity with an unsubstituted triazole ring, and to find out how the introduction of amino and mercapto substituents affects the aromaticity of the systems under study. For this purpose, the aromaticity indexes HOMA and I (Bird) of substituted derivatives of 1,2,4-triazole were compared. As model objects, we have selected: 1H-1,2,4-triazol-5-amine, 4H-1,2,4-triazol-3-amine, 5-amino-4H- 1,2,4-triazol-1-ium cation, 1H-1,2,4-triazole-3-thiol, 4H-1,2,4-triazole-3-thiol, 3-sulfanyl-4H-1,2,4- triazol-1-ium cation, 5-amino-1H-1,2,4-triazole-3-thiol, 5-amino-4H-1,2,4-triazole-3-thiol, 5-amino-3- sulfanyl-4H-1,2,4-triazol-1-ium cation, and corresponding unsubstituted triazoles were selected as reference substances: 1H-1,2,4-triazole, 4H-1,2,4-triazole, 4H-1,2,4-triazol-1-ium cation. Model molecules were optimized using the PBE/6-311G ** density functional method in the PRIRODA program. The HOMA and I (Bird) aromaticity indices were calculated using the Multiwfn program. The results showed that 1-substituted triazoles for about 7÷14 kcal/mol more stable than 4- substituted analogs. The introduction of a mercapto-group to the triazole system slightly reduces the aromatic character of the cycle, whereas the introduction of an amino-group significantly reduces the aromaticity. Such changes in the aromatic nature of the triazole cycle are due to deviations in the interatomic distances of the triazole cycle. It has been found that N1-N2, N4-C5, and N2-C3 have the most significant influence on the aromatic change of substituted triazoles. Keywords: 1,2,4-triazole; DFT; aromaticity; HOMA; Bird.