A dimer of HCN, N-cyanomethanimine 6, was prepared by flash pyrolysis (gas phase, mbar) from 3-azido-1,2,4-triazole l a and detected by ultraviolet photoelectron spectroscopy (HeI). Its ionization potentials were measured and the ionic states sequence proposed, with the aid of ab inifio -CI (configuration interaction) calculations. ' The study of the MNDO potential hypersurface enabled us to propose a mechanism of the thermal reorganization of the precursor l a . It is shown that the reaction path passes through the formation of the protomer l b before thermal decomposition and the generation of the nitrene 2b.
R e p le I l mars 1988 I. B'SHARY, C. GUIMON, M. GRIMAUD et G. PFISTER-GUILLOUZO. Can. J. Chem. 66,2830Chem. 66, (1988. La flash thermolyse du methyl-5 azido-2 thiadiazole-1,3,4 sous pression rCduite (lo-' mbar) a CtC suivie par spectroscopie photoClectronique ultraviolette (HeI). Elle conduit a I'obtention du thiocktkne H2C=C=S accompagnC d'acide cyanhydrique HCN et d'azote N2. La formation de ces molCcules montre que le thiadiazolo-nitrkne instable subit une ouverture de cycle pour donner une thione IinCaire 4 qui se rkarrange thermiquement dans les produits finals. Ce dernier rkarrangement est analysC theoriquement a l'aide de la mCthode semi-empirique MNDO.I. B'SHARY, C. GUIMON, M. GRIMAUD, and G. PFISTER-GUILLOUZO. Can. J. Chem. 66,2830Chem. 66, (1988. The flash thermolysis of 5-methyl 2-azido 1,3,4-thiadiazole (vapour phase: lo-' mbar) was studied by ultraviolet photoelectron spectroscopy (HeI). The products detected (H2C=C=S, HCN, and N7) suggest that the unstable thiadiazole-nitrene undergoes a ring opening to form a linear thione 4, which generates the thiocetene H2C=C=S. This step was theoretically analysed by the MNDO method.Les azotures sont utilisCs depuis de nombreuses anntes comme precurseurs de molCcules i courte durCe de vie aussi bien par photolyse que par thermolyse car, perdant relativement facilement une molCcule d'azote, ils gCnkrent un nitrkne instable qui se rCarrange aussitht en composCs stables ou mitastables
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