Investigation of 4-(Nitrophenylamino)Pent-3-En-2-Ones and 4-(Nitrobenzylamino)Pent-3-en-2-Ones by Electron Ionization Mass Spectrometry. Observation of Characteristic Ortho Effects

Abstract

The compounds 4-(phenylamino)pent-3-en-2-ones (1–3) and 4-(benzylamino)pent-3-en-2-ones (4–6) substituted with a nitro group on the aromatic ring were studied by electron ionisation mass spectrometry (EIMS). It was deduced that the compounds 1–3 are converted into the tautomeric 4-(arylimino)pentan-2-one during the EI process. Mass spectrometric decompositions of ortho-substituted derivatives (1 and 4) were found to be different from those observed for meta- and para-isomers. The fragmentation pathways are discussed on the basis of data from linked B/E and B2/E scans, mass-analysed ion kinetic energy (MIKE) spectra, accurate mass measurements and isotope labelling.