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Intermediate ion structures in the fragmentation of metastable 3‐methylbutan‐2‐ol radical cations
Author(s) -
George M.,
Holmes John L.
Publication year - 1990
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.1210251108
Subject(s) - chemistry , isotopomers , dissociation (chemistry) , ion , metastability , deuterium , propane , fragmentation (computing) , molecule , bond cleavage , mass spectrum , bond dissociation energy , kinetic isotope effect , electron ionization , collision induced dissociation , polyatomic ion , crystallography , ionization , mass spectrometry , tandem mass spectrometry , atomic physics , organic chemistry , physics , chromatography , computer science , catalysis , operating system
Ionized 3‐methylbutan‐2‐ol displays four low‐energy fragmentations, loss of CH 3 · and C 3 H 7 · and loss of CH 4 and C 3 H 8 , the latter pair being produced by metastable ion decompositions. The electron‐impact, metastable‐ion and collision‐induced dissociation mass spectra of 13 C and 2 H‐labelled isotopomers have been recorded, together with appearance energy measurements. It was found that the fast (ion source) losses of CH 3 · and C 3 H 7 · involved only simple bond cleavages between C(1) and C(2) and between C(2) and C(3), respectively, and without any positional interchange of isotopes. The loss of C 3 H 8 produces ionized vinyl alcohol containing only C(l) and C(2). The H atoms involved are only those attached to C(1) and C(3). In deuterium‐labelled analogues, the deuterium is preferentially located in the propane, e.g. metastable CD 3 CH(OH)CH(CH 3 ) 2 yields predominantly C 3 H 6 D 2 . On the basis of all the observations, it is proposed that low‐energy molecular ions can form a stable proton‐bridged molecule‐radical complex, \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm HOCHCH}_2 \cdots \mathop {\rm H}\limits^{\rm + } \cdots \mathop {\rm C}\limits^{\rm .} {\rm H}({\rm CH}_3)_2] $\end{document} , and that this key intermediate is responsible for the isotope distribution in propane loss and also for the relatively low importance of the lowest energy dissociation, the simple C(1)C(2) bond cleavage.