The fragmentation of 2‐aminooxazoles under electron impact

The 70 eV electron impact mass spectra of six 2‐aminooxazoles are discussed in detail with the aid of exact mass measurements, metastable ion detection in the defocused mode and labelling experiments. The fragmentation is markedly influenced by strong electron donating substituents at the 2‐position. Some 2‐acetylamino and 2‐diacetylamino derivatives have also been considered, which lose ketene from [M]+⋅ giving the corresponding aminooxazole molecular ions. The mass spectral behaviour is peculiar and the most important differences between the fragmentation pathways of these compounds and those reported in the literature for oxazole (alkyl and aryl) derivatives are outlined. The mass spectrum of 4‐methyl‐5‐phenylimidazol‐2‐one is compared with that of the isomeric 4‐methyl‐5‐phenyl‐2‐aminooxazole.