The pyrolysis of 4-arylideneimino-1,2,4-triazol-3(2H)-one (ATO) and its analogues was investigated by the density functional theory method at the B3LYP/6-31＋＋G(d,p) level of theory. The substituent and temperature effects on the title reaction have been discussed from the aspects of thermodynamic properties, geometric parameters, and natural population analysis. The calculated results show that the substituent R has little effect on the reaction, while the changes caused by the substituents Y on the benzene ring (Y＝MeO, Me, H, Cl, and NO2) in the corresponding activation free energies (ΔG≠), bond lengths (ΔR≠), bond angles (Δα≠), and atomic charges (Δq≠) have linear correlations with Hammet constant (σ): ΔP≠＝ρσ＋C, (P＝G, R, α and q, r＞0.95). The electron-donating group decreases the activation free energies and bond lengths, but increases the bond angles and natural electric charges. By contraries, the electron-withdrawing group has the opposite effect.

Key words: 4-arylideneimino-1,2,4-triazol-3(2H)-ones, pyrolysis, the density functional theory, substituent effectfunctional theory, substituent effect