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The gas phase ion chemistry of the acetyl cation and isomeric [C 2 H 3 O] + ions. On the structure of the [C 2 H 3 O] + daughter ions generated from the enol of acetone radical cation
Author(s) -
Burgers Peter C.,
Holmes John L.,
Szulejko Jan E.,
Mommers Alexander A.,
Terlouw Johan K.
Publication year - 1983
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.1210180607
Subject(s) - metastability , ion , isomerization , chemistry , physics , fragmentation (computing) , crystallography , atomic physics , stereochemistry , quantum mechanics , computer science , operating system , catalysis , biochemistry
Methods are described for the unequivocal identification of the acetyl, [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] ( a ), 1‐hydroxyvinyl, [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} OH] ( b ), and oxiranyl, ( d ), cations. They involve the careful examination of metastable peak intensities and shapes and collision induced processes at very low, high and intermediate collision gas pressures. It will be shown that each [C 2 H 3 O] + ion produces a unique metastable peak for the fragmentation [C 2 H 3 O] + → [CH 3 ] + +CO, each appropriately relating to different [C 2 H 3 O] + structures. [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] ions do not interconvert with any of the other [C 2 H 3 O] + ions prior to loss of CO, but deuterium and 13 C labelling experiments established that [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} OH] ( b ) rearranges via a 1,2‐H shift into energy‐rich leading to the loss of positional identity of the carbon atoms in ions ( b ). Fragmentation of b to [CH 3 ] + +CO has a high activation energy, c. 400 kJ mol −1 . On the other hand, , generated at its threshold from a suitable precursor molecule, does not rearrange into [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} OH], but undergoes a slow isomerization into [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] via [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} HO]. Interpretation of results rests in part upon recent ab initio calculations. The methods described in this paper permit the identification of reactions that have hitherto lain unsuspected: for example, many of the ionized molecules of type CH 3 COR examined in this work produce [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} OH] ions in addition to [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] showing that some enolization takes place prior to fragmentation. Furthermore, ionized ethanol generates a , b and d ions. We have also applied the methods for identification of daughter ions in systems of current interest. The loss of OH ˙ from [CH 3 COOD] +˙ generates only [CH 2 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} OD]. Elimination of CH 3 ˙ from the enol of acetone radical cation most probably generates only [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} O] ions, confirming the earlier proposal for non‐ergodic behaviour of this system. We stress, however, that until all stable isomeric species (such as [CH 3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{\rm + } $\end{document} C:]) have been experimentally identified, the hypothesis of incompletely randomized energy should be used with reserve.