Theoretical study on mechanism of decomposition reaction of 1,2,4-triazole derivatives

The internal connection between the electronic structure and decomposition mechanism for ANTA and AHNTA is investigated by DFT method. The molecular electrostatic potential shows that hydrogen atoms of the amino group are easily transferred to the nitro group. The excitation process of S₀→T₁ can be regarded as the local $\pi \to \pi \ast$ excitation. For the substituent dissociation, amino group is easily separated from the ring. For the ring cleavage, the C–N bond will be weakened by substituents on the C and N atoms. Especially at the excited state, the C–N bond with a nitro group on the C atom is the easiest to break. The charged state is beneficial to CONO isomerisation, and the H transfer is promoted at the excited state. For ANTA, the reaction rate of CONO isomerisation is faster than ring cleavage at the ground or the positively charged state. At the negatively charged state, the reaction rate of H transfer is the fastest. For AHNTA, at the ground state or the charged state, the reaction rate of CONO isomerisation is the fastest, compared to ones of the H transfer and ring cleavage reactions. At the excited state, the order is k_{(H transfer)}>k_{(ring cleavage)} for ANTA and AHNTA.