Fragmentation d'azoles sous l'impact electronique. X—etude de rearrangements cycliques en serie alkylamino-1,2,4-triazole

In situ generation of the individual tautomers by fragmentation reactions in the mass spectrometer is shown to provide a means of studying rearrangements of the type involved in prototropic equilibria. C-aminotriazole was generated in different tautomeric forms by ethylene elimination from the N-ethyl compounds and the tautomers were shown to equilibrate prior to further fragmentation. Ethylene elimination was shown by characterising the energy partitioning associated with the metastable ion reactions to occur via a four centred transition state from two ethylamino-triazole isomers and via a five centred transition state from the third. These mechanistic conclusions were supported by characterising frequency factors through measurements of kinetic isotope effects. Propene elimination from the corresponding propylaminotriazoles was studied by analogous methods. Energy partitioning and kinetic isotope effect studies were in agreement with a stepwise elimination of propene, or with a five centred β-hydrogen transfer mechanism.