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 va rious competing mechanisms involved in the early stages of the decompositio n of a "push-pull" (containing both electron-donating and withdrawing group s) aromatic (1,3,5-triamino-2,4,6-trinitrobeznene, TATE), and particularly how hydrogen transfer affects the competition between ring closure and sing le bond scission. On the basis of the obtained energetics, we found several previously suggested mechanisms to be energetically disfavored. These mech anisms include direct N-H, N-O, C-NH2 bond dissociation, carbon ring cleava ge, and the production of NO2-1 anion. Our results indicate that the rate-l imiting 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 t o further decomposition products, such as benzofurazans.