6533b822fe1ef96bd127d65d

RESEARCH PRODUCT

Studies in organic mass spectrometry. Part 20: a hidden ortho effect in the electron ionisation mass spectra of some 2′-alkyl substituted 2-and 3-thiophenecarboxanilides

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The electron-ionisation-induced amide-bond cleavage of some 2′-methyl- and 2′-ethyl-substituted 2- and 3-thiophenecarboxanilides, which yields formally anilylium ions having relative intensities apparently in contrast with the Stevenson‐Audier rule, has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry and compared to that of the 3 ′- and 4′-isomers. It has been shown that, in the case of the 2 ′-methyl and 2′-ethyl derivatives, the amide-bond cleavage is anchimerically assisted through the hidden migration of a benzyl hydrogen to the nitrogen. Analysis of the MIKE and collision-induced decomposition (CID) MIKE spectra of model compounds indicates that this cryptic ortho effect produces a stable ortho quinoide or aminotropylium structure.