Abstract

AbstractNot only strongly basic aromatic amines such as ‘proton sponges’ show characteristic [M – Me2NH – H]+ peaks corresponding to cyclization to stable heterocyclic ions under electron impact. The fragmentation of the title compounds, which are weak bases, leads to [M – RNH2 – C6H5]+ heteroaromatic ions. These are the 7‐phenyl‐7H‐benz[kl]acridine radical cation and the delocalized stable 7H‐benz[kl]acridin‐7‐ylium ion as shown by unimolecular metastable ion spectra, collision‐induced decomposition (CID) tandem mass spectrometry (MS/MS) and accurate mass measurements. The high‐collision‐energy CID tandem mass spectra of these ions are perfectly superimposable on those of the ions produced by the reference substance, 7‐phenyl‐7H‐benz[kl]acridine obtained as a by‐product in the Ullmann phenylation of 1,8‐diaminonaphthalene. This combination of MS/MS experiments also provides strong support for the gas‐phase reaction mechanism leading to the benz[kl]acridine ions and for the structures of these ions.

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