Ring closure mediated by intramolecular hydrogen transfer in the decomposition of a push-pull nitroaromatic: TATB

Using gradient-corrected density functional theory, we have investigated various competing mechanisms involved in the early stages of the decomposition of a push-pull (containing both electron-donating and withdrawing groups) aromatic (1,3,5-triamino-2,4,6-trinitrobeznene, TATE), and particularly how hydrogen transfer affects the competition between ring closure and single bond scission. On the basis of the obtained energetics, we found several previously suggested mechanisms to be energetically disfavored. These mechanisms include direct N-H, N-O, C-NH(2) bond dissociation, carbon ring cleavage, and the production of NO(2)(-1) anion. Our results indicate that the rate-limiting step is ring closure mediated by intramolecular hydrogen transfer. This mechanism is predicted to have a barrier height of 47.5 kcal/mol. The hydrogen motion forms a biradical state which we suggest is the precursor to further decomposition products, such as benzofurazans.