Proximity Effects in the Electron Impact Mass Spectra of 2-Substituted Benzazoles
Chantler, Thomas Perrin, Victoria L. Donkor, Rachel E. Cawthorne, Richard S. Bowen, Richard D.
Chantler, Thomas
Perrin, Victoria L.
Donkor, Rachel E.
Cawthorne, Richard S.
Bowen, Richard D.
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2004
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Abstract
The 70 eV electron impact mass spectra of a wide range of 2-substituted benzazoles are reported and discussed. Particular attention is paid to the mechanistic significance and analytical utility of [M–H]+ and [M–X]+ signals in the spectra of benzazoles in which the 2-substituent contains a terminal aryl group with one or more substituents, X. Loss of H or X occurs preferentially from an ortho-position from ionized 2-benzylbenzimidazoles, 2-phenethylbenzimidazoles, 2-styrylbenzimidazoles, 2-styrylbenzoxazoles and 2-styrylbenzothiazoles. In the three styrylbenzazole series, the [M–H]+ and/or [M–X]+ signals dominate the spectra. This unusually facile loss of H or X may be attributed to a proximity effect, in which cyclization of the ionized molecule is followed by elimination of an ortho-substituent to give an exceptionally stable polycyclic ion. Formation of a new five- or six-membered ring by the proximity effect occurs rapidly; cyclization to a seven-membered ring takes place rather less readily; but formation of a ring with only four atoms or more than seven atoms is not observed to a significant extent. The proximity effect competes effectively with loss of a methyl radical by simple cleavage of an ethyl, isopropyl and even a t-butyl group in the pendant aromatic ring of ionized 2-(4-alkylstyryl) benzazoles.
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Chantler T, Perrin VL, Donkor RE, Cawthorne RS and Bowen RD (2004) Proximity Effects in the Electron Impact Mass Spectra of 2-Substituted Benzazoles. International Journal of Mass Spectrometry. 236 (1-3): 65-80.
Special issue: In honour of Dudley H. Williams.
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