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Les spectres de masse des aryl-2 alkyl-4 oxadiazol-1,3,4 ones-5 et de leurs isomeres aryl-2 alcoxy-5 oxadiazoles-1,3,4 ont ete etudies. La fragmentation de ces composes ne semble pas faire intervenir d'isomerisation unimoleculaire d'origine electronique. Pour chaque type d'heterocycle, les transferts d'hydrogene accompagnant la pete de la chaine alcoylee sont principalement induits par l'azote 4. The mass spectra of 2-aryl-4-alkyl-1,3,4-oxadiazole-5-ones and their 2-aryl-5-alkoxy 1,3,4-oxadiazole isomers have been studied. Unimolecular electron impact-induced isomerization does not seem to occur during the fragmentation of these compounds. For each type of heterocycle, the hydrogen transfers, during the cleavage of the alkyl chain, are mainly caused by the nitrogen in position 4.

Les spectres de masse d'un certain nombre d'amino-4 triazole-1,2,4 ones-5 differemment substituees en position 1 sont rapportes; ils mettent en evidence de nouveaux rearrangements et des migrations d'hydrogene. La comparaison des spectres normaux et des spectres d'energie cinetique obtenus selon la technique simili MIKE a permis de determinerla structure des ions moleculaires et des ions fragments et de decrirela formation de ces derniers. Ces resultats montrent que ľion moleculaire des amino-4 triazolones-5 non substituees en position 1 existe probablement en phase gazeuse sous deux formes tautomeres (N-1-H et OH). The mass spectra of several 4-amino-1,2,4-triazole-5-ones with different groups in position 1 have been recorded and show new skeletal rearrangements and hydrogen migrations. The comparison of the ‘normal’ and mass analysed ion kinetic energy spectra obtained by the ‘simili MIKE’ technique permits the determination of the molecular ion and fragment ion structures and also the mechanism of formation of these ions. These results show that the molecular ion of the N-1 unsubstituted 4-amino-1,2,4-triazole-5-ones exists in the gas phase in two tautomeric forms.