Mecanisme De Decarbonylation De Pyrazolides Ionises Par Impact Electronique

Electron impact ionization of 1-acryloylpyrazole [1] induces a unimolecular loss of CO forming ionized 1-vinylpyrazole [2] as shown by metastable ion characteristics and neutralization-reionization data. This CO loss implies a rate-determining isomerization process into a pyrazolylmethyl ketene structure 1a+. These ketene ions have been synthetized in the ion source by dissociative ionization of pyrazolylpropionylpyrazoles. Flash-vacuum pyrolysis of these compounds also affords the expected neutral ketenes in the gas phase, which are however readily converted into the acryloyl isomers by an intramolecular nucleophilic process.