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

Eur. J. Mass Spectrom. 2, 49–55 (1996)
DOI: 10.1255/ejms.79

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

Leopoldo Ceraulo, Mirella Ferrugia and Liliana Lamartina
Dipartimento di Chimica e Tecnologie Farmaceutiche, Via Archirafi 32, I-90123 Palermo, Italy.
Salvatore Foti and Rosaria Saletti
Dipartimento di Scienze Chimiche, Viale A. Doria 6, I-95125 Catania, Italy.
Domenico Spinelli^*
Dipartimento di Chimica Organica "A. Mangini", Via S. Donato 15, I-40127 Bologna, Italy.

ABSTRACT:

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.

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