Theoretical study of gas-phase formation enthalpies and isomerism for 4(5)-nitro-1,2,3-triazole and its N-alkyl derivatives and experimental determination of formation enthalpy for 2-methyl-4-nitro-1,2,3-triazole

The formation enthalpies of tautomeric forms of 1,2,3-triazole, 4(5)-nitro-1,2,3-triazole and isomeric N-alkyl-4(5)-nitro-1,2,3-triazoles (alkyl = methyl, ethyl, isopropyl and tert-butyl) have been calculated with the density functional theory B3LYP method by means of designed isolobal, isodesmic and isomerisation reactions. The experimental ideal-gas formation enthalpy of 2-methyl-4-nitro-1,2,3-triazole has been determined based on the formation enthalpy in the crystalline state and the sublimation enthalpy. The experimental value of formation enthalpy (228.7 ± 3.5 kJ mol−1) is in good agreement with the one obtained from reaction enthalpy calculations (233.5 kJ mol−1). The relative Gibbs energies for tautomeric forms of 1,2,3-triazole and 4(5)-nitro-1,2,3-triazole and isomeric N-alkyl-4(5)-nitro-1,2,3-triazoles in aqueous solution have also been calculated using the Conductor polarized continuum model (CPCM). The results of the calculations have been discussed concerning the relative stability of the titled compounds.