Theoretical study on the thermal decomposition of azoisobutyronitrile

The thermal decomposition mechanisms of azoisobutyronitrile (AIBN) in ground state have been investigated systematically. Based on the potential energy surfaces of various possible dissociation paths obtained using semiempirical AM1 method with partial optimization, the density function theory B3LYP/6-311G* method was employed to optimize the geometric parameters of reactant, possible intermediates and products, which were further confirmed with vibrational analysis. The obtained results show that the two-bond dissociation of Me-2(CN)C-N kN=N-CN)Me-2 --> 2Me(2)(CN)C-. + N-2 is much more favorable than the two one-bond dissociation processes of Me-2(CN)CN-NC(CN)Me-2 --> Me-2(CN)CN=N-. + Me-2(CN)C-. --> 2Me(2)(CN)C-. + N-2. It was suggested that the electron shrink effect of double bond (-N =N-) in AIBN and the stabilities of the formed Me-2(CN)C-. radical and N-2 lead to the reaction proceeding in the former pathway. Our calculations rationalize and verify all the experimental facts. (C) 2004 Elsevier B.V. All rights reserved.