The conformational properties and the photolysis behavior of one of the simplest N-C bonded bicyclic azoles, 5-(1H-tetrazol-1-yl)-1,2,4-triazole (T), were studied in argon and xenon matrices by infrared spectroscopy. Analysis of the experimental results was supported by extensive theoretical calculations carried out at the B3LYP/6-311++G(2d,2p) level of approximation. Out of the eight T minima located on the potential energy surface, the three most stable species were detected in low temperature matrices, namely, 5-(1H-tetrazol-1-yl)-1H-1,2,4-triazole (T1) and two conformers of 5-(1H-tetrazol-1-yl)-2H-1,2,4-triazole (T2a and T2b). With increase of the substrate temperature either during deposition of the matrices or during annealing the T2b -> T2a conversion took place, in agreement with the predicted low energy barrier for this transformation (5.38 kJ mol(-1)). Both broad band and narrow band laser UV irradiations of T isolated in Xe and Ar matrices induce unimolecular decomposition involving cleavage of the tetrazole ring of T1 and T2a (T2b) that leads to the production of 1H-1,2,4-triazol-5-yl carbodiimide (P1) and 1H-1,2,4-triazol-3-yl carbodiimide (P2), respectively. When the laser is used, in addition to the main P1 and P2 photoproducts, several minor products could be successfully identified in the matrices: N-cyanocarbodiimide HNCNCN (detected for the first time) associated with nitrilimine HNNCH and HCN. An interesting phenomenon of tautomer-selective photochemistry was observed for the matrix-isolated compound. It could be explained by the different LUMO-HOMO energy gaps estimated for T1, T2a, and T2b, connected with different threshold energies necessary to start the photolysis of T1 and T2a (T2b).

M. Pagacz-Kostrzewa, I. D. Reva, R. Bronisz, B. M. Giuliano, R. Fausto, M. Wierzejewska (2011). Conformational Behavior and Tautomer Selective Photochemistry in Low Temperature Matrices: The Case of 5-(1H-Tetrazol-1-yl)-1,2,4-triazole. JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY, 115(22), 5693-5707 [10.1021/jp202925r].

Conformational Behavior and Tautomer Selective Photochemistry in Low Temperature Matrices: The Case of 5-(1H-Tetrazol-1-yl)-1,2,4-triazole

GIULIANO, BARBARA MICHELA;
2011

Abstract

The conformational properties and the photolysis behavior of one of the simplest N-C bonded bicyclic azoles, 5-(1H-tetrazol-1-yl)-1,2,4-triazole (T), were studied in argon and xenon matrices by infrared spectroscopy. Analysis of the experimental results was supported by extensive theoretical calculations carried out at the B3LYP/6-311++G(2d,2p) level of approximation. Out of the eight T minima located on the potential energy surface, the three most stable species were detected in low temperature matrices, namely, 5-(1H-tetrazol-1-yl)-1H-1,2,4-triazole (T1) and two conformers of 5-(1H-tetrazol-1-yl)-2H-1,2,4-triazole (T2a and T2b). With increase of the substrate temperature either during deposition of the matrices or during annealing the T2b -> T2a conversion took place, in agreement with the predicted low energy barrier for this transformation (5.38 kJ mol(-1)). Both broad band and narrow band laser UV irradiations of T isolated in Xe and Ar matrices induce unimolecular decomposition involving cleavage of the tetrazole ring of T1 and T2a (T2b) that leads to the production of 1H-1,2,4-triazol-5-yl carbodiimide (P1) and 1H-1,2,4-triazol-3-yl carbodiimide (P2), respectively. When the laser is used, in addition to the main P1 and P2 photoproducts, several minor products could be successfully identified in the matrices: N-cyanocarbodiimide HNCNCN (detected for the first time) associated with nitrilimine HNNCH and HCN. An interesting phenomenon of tautomer-selective photochemistry was observed for the matrix-isolated compound. It could be explained by the different LUMO-HOMO energy gaps estimated for T1, T2a, and T2b, connected with different threshold energies necessary to start the photolysis of T1 and T2a (T2b).
2011
M. Pagacz-Kostrzewa, I. D. Reva, R. Bronisz, B. M. Giuliano, R. Fausto, M. Wierzejewska (2011). Conformational Behavior and Tautomer Selective Photochemistry in Low Temperature Matrices: The Case of 5-(1H-Tetrazol-1-yl)-1,2,4-triazole. JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY, 115(22), 5693-5707 [10.1021/jp202925r].
M. Pagacz-Kostrzewa;I. D. Reva;R. Bronisz;B. M. Giuliano;R. Fausto;M. Wierzejewska
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/396074
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