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Eur. J. Mass Spectrom. 2, 33 - 42 (1996) |
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| Anionic migration in aromatic systems effected by collisional activation. Unusual fragmentations of deprotonated anilides containing methoxyl and ethoxyl substituents | ||
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Stephen J. Blanksby, Suresh Dua, John M. Hevko, Hamish Christie and John H. Bowie |
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| ABSTRACT: | ||
| Long-range cross-ring reactions occur when (M H) ions of methoxy- and ethoxy-C6H4NCOR (R = H, CH3, C6H5 and CH3O) are subjected to collisional activation. These reactions are generally minor processes: a particular example is the cross-ring elimination p-C2H5OC6H4NCOCH3< [CH3 (p-C2H5OC6H4NCO)]< p-(O)C6H4NCO+ C2H4 + CH4. Major processes of these (M H) ions involve (i) losses of radicals to form stabilised radical anions, e.g. (a) loss of a ring H" or (b) CH3" (or C2H5") from the alkoxy group, and (ii) proximity effects when the two substituents are ortho, e.g. loss ofCH3OH from o-CH3OC6H4NCHO yields deprotonated benzoxazole. Another fragmentation of an arylmethoxyl anion involves loss of CH2O. It is proposed that losses of CH2O are initiated by anionic centres but the actual mechanisms in the cases studied depend upon the substitution pattern of the methoxyanilide: o- and p-methoxyanilides may undergo ipso proton transfer/elimination reactions, whereas the m-analogues undergo proton transfer reactions to yield an o-CH3O substituted aryl carbanion followed by proton transfer from CH3O to the carbanion site with concomitant loss of CH2O. | ||
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Keywords: ortho effect, 2-methylbenzylalcohol radicalcation, 2-methylbenzoic acid radical cation, distonic ion, fragmentation mechanism. |
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