ONIOM calculation was carried out to investigate the isomerization and dissociation reactions of nitramide (NA) encapsulated inside an armchair (5,5) single-walled carbon nanotubes [NA@CNT(5.5)]. Results demonstrated that the activation energy barriers of the N-N bond dissociation and the nitro-nitrite isomerization of NA significantly decreased when NA was encapsulated inside CNT(5,5), suggesting that the CNT(5,5) can promote the two initial reactions. However, the H-migration reaction of NA was hindered by the encapsulation inside CNT(5.5) in view of the increase in the barrier height. The encapsulated inside CNT(5,5) resulted in the exchange of the order of energy barriers for the N-N bond dissociation and H-migration isomerization. The H-migration reaction was kinetically favorable for the isolated NA, but the N-N bond dissociation was the most energetically favorable for the NA@CNT(5.5). Results also showed that, in the encapsulated state, the H-migration reaction could compete vigorously with the N-N bond dissociation due to their close activation energies. Furthermore, we found that the relative energies of the intermediates formed by the isomerization and dissociation of NA were also modified by the encapsulation inside CNT(5,5). (C) 2011 Elsevier B.V. All rights reserved.