A donor atom stabilized borylnitrene, 2-nitreno-1,3,2-benzodioxaborole 4c, is characterized by matrix isolation IR, UV, and ESR spectroscopy as well as multiconfiguration SCF and CI computations. UV irradiation (λ ) 254 nm) of the corresponding azide 6c, isolated in solid argon at 10 K, produces 4c in high yield. The oxygen donor atoms in 4c result in a triplet ground state (|D/hc| ) 1.492 cm -1 , |E/hc| ) 0.004 cm -1 ) for the borylnitrene. The lowest energy singlet state ( 1 A1) is 33 kcal mol -1 higher in energy and closely related to the ground state of vinylidene. Under the conditions of matrix isolation, triplet 4c is photochemically and thermally stable toward rearrangement to the corresponding cyclic iminoborane. Photochemical irradiation (λ > 550 nm) of 4c rather causes an efficient reaction with molecular nitrogen, lying in matrix sites nearby, to give 6c. Similarly, photochemical, but not thermal, trapping of 4c with CO is possible and results in the corresponding isocycanate 9c. Thermal reaction of 4c with O 2 in doped argon matrixes at 35 K could be observed by IR spectroscopy to result in borylnitroso-O-oxide 17c as shown by 18 O2 labeling experiments and DFT computations. The diradical 17c is very photolabile and quickly rearranges to the nitritoborane 16c upon irradiation.
The Curtius rearrangement is a synthesis of isocyanates (R-N=C=O) by thermal or photochemical rearrangement of acyl acides and/or acylnitrenes. The photochemical rearrangement of benzoyl azide is now shown for the first time to pro-[a] Chemistry Scheme 1.
The decomposition mechanism of 2-ethyl-hexylnitrate (2-EHN), an important additive to diesel fuel to improve the cetane number, was investigated in solution and in the gas phase. In trans-decalin as solvent, an activation barrier for the thermal decomposition of 39 kcal/mol was determined, and thus the decomposition is slow at temperatures below 100 • C. Under high pressure conditions (2.4 kbar) the decomposition rates decrease, in accordance with a radical mechanism. Flash vacuum pyrolysis with subsequent detection of the products via mass spectroscopy or matrix IR spectroscopy allows to identify NO 2 , formaldehyde, and several olefins as the major decomposition products. These data allow proposing a consistent mechanistic scheme for the 2-EHN decay.
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