1H/2H and azide/tetrazole isomerizations and their effects on the aromaticity and stability of azido triazoles

Abstract

Isomerization is one of the most curious aspects of organic chemistry. In this work, 1H/2H and azide/tetrazole (AZ/TZ) isomerizations in 3-nitro-5-azido-1,2,4-triazole (NAzTA), 3-amino-5-azido-1,2,4-triazole (AAzTA), and 5-azido-1,2,4-triazole (AzTA) were studied using the density functional theory method. The 1H/2H tautomerization proceeds most easily for AAzTA while hardest for NAzTA, suggesting that –NH₂ facilitates the process, while –NO₂ gives an opposite effect. The AZ/TZ isomerization takes place most easily for AzTA, and then AAzTA and NAzTA in sequence, revealing that this kind of isomerization more easily proceeds in the molecule with only the –N₃ group and substitution of –NH₂ or –NO₂ prevents the process. The AZ/TZ isomerization is much easier than the 1H/2H tautomerization. For the azide isomers, the triazole ring has higher aromaticity in the 1H-tautomer than in the 2H-form, i.e., tautomerization from 1H to 2H isomer makes the stability decrease. For the tetrazole isomers, both the triazole ring and the tetrazole ring have high aromaticity. One more aromatic ring in the tetrazole isomers implies an increase in the stability by the isomerization from an azide to tetrazole.