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Loss of methyl radical from some small immonium ions: Unusual violation of the even‐electron rule
Author(s) -
Bowen Richard D.,
Harrison Alex G.
Publication year - 1981
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210160408
Subject(s) - metastability , ion , dissociation (chemistry) , physics , chemistry , crystallography , atomic physics , analytical chemistry (journal) , stereochemistry , quantum mechanics , chromatography
Abstract Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R 1 , R 2 , R 3 = H or alkyl) eliminate . CH 3 ; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even‐electron rule, which states that closed‐shell cations usually decompose to give closed‐shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH 3 ) 2 CNH] +. ) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH 3 . and CD 3 . , via different mechanisms, but very little CH 2 D . or CHD 2 . loss occurs.