Theoretical study on thermal decomposition of azoisobutyronitrile in ground state

The thermal decomposition mechanisms of azoisobutyronitrile (AIBN) in the ground state have been investigated systematically. Based on the potential energy surfaces (PIES) of various possible dissociation paths obtained using the semiempirical AM1 method with partial optimization, the density function theory B3LYP/6-311G* method was employed to optimize the geometric parameters of the reactants, the intermediates, the products and the transition states, which were further confirmed by the vibrational analysis. The obtained results show that the reaction process of the two-bond (three-body) simultaneous cleavage Me-2(CN)C-N=N-C(CN)Me-2-->2Me(2)(CN)C. +N-2 is much more favorable than the reaction process of the two onebond asynchronous cleavage Me-2(CN)CN=N-C(CN)Me-2-->Me-2(CN)CN=N- + Me-2(CN)C. --> Me-2(CN)C. + N-2. It was suggested that the electron shrinking effect of double bond (-N=N-) in AIBN and the stabilities of the Me-2(CN)C. radical as well as N-2 molecule are main factors of leading to the reaction proceeding in the former pathway. The calculation results were consistent with all the experimental facts.