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Structure and mechanism of fragmentation of [C 2 H 5 O] +
Author(s) -
Keyes B. G.,
Harrison A. G.
Publication year - 1974
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.1210090210
Subject(s) - chemistry , fragmentation (computing) , protonation , electron ionization , hydrogen , ion , deuterium , ionization , chemical ionization , oxygen , dissociation (chemistry) , photochemistry , medicinal chemistry , organic chemistry , physics , quantum mechanics , computer science , operating system
The decomposition reactions of [C 2 H 5 O] + ions produced by dissociative electron‐impact ionization of 2‐propanol have been studied, using 13 C and deuterium labeling coupled with metastable intensity studies. In addition, the fragmentation reactions following protonation of appropriately labeled acetaldehydes and ethylene oxides with [H 3 ] + or [D 3 ] + have been investigated. In both studies particular attention has been paid to the reactions leading to [CHO] + , [C 2 H 3 ] + and [H 3 O] + . In both the electron‐impact‐induced reactions and the chemical ionization systems the fragmentation of [C 2 H 5 O] + to both [H 3 O] + and [C 2 H 3 ] + proceeds by a single mechanism. For each case the reaction involves a mechanism in which the hydrogen originally bonded to oxygen is retained in the oxygen containing fragment while the four hydrogens originally bonded to carbon become indistinguishable. The fragmentation of [C 2 H 5 O] + to produce [CHO] + proceeds by a number of mechanisms. The lowest energy route involves complete retention of the α carbon and hydrogen while a higher energy route proceeds by a mechanism in which the carbons and the attached hydrogens become indistinguishable. A third distinct mechanism, observed in the electron‐impact spectra only, proceeds with retention of the hydroxylic hydrogen in the product ion. Detailed fragmentation mechanisms are proposed to explain the results. It is suggested that the [C 2 H 5 O] + ions formed by protonation of acetaldehyde or ionization of 2‐propanol are produced initially with the structure [CH 3 CH \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document} H] (a), but isomerize to [CH 2 CH \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document} H 2 ] (e) prior to decomposition to [C 2 H 3 ] + or [H 3 O] + . The results indicate that the isomerization a → e does not proceed directly, possibly because it is symmetry forbidden, but by two consecutive [1,2] hydrogen shifts. A more general study of the electron‐impact mass spectrum of 2‐propanol has been made and the fragmentation reactions proceeding from the molecular ion have been identified.