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Methoxymethyl cation [CH 3 OCH 2 ] + revisited: Experimental and theoretical study
Author(s) -
Audier H. E.,
Bouchoux G.,
McMahon T. B.,
Milliet A.,
Vulpius T.
Publication year - 1994
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.1210290404
Subject(s) - chemistry , fourier transform ion cyclotron resonance , dissociation (chemistry) , deuterium , kinetic energy , kinetic isotope effect , mass spectrometry , ion cyclotron resonance , ion , delocalized electron , hydrogen , analytical chemistry (journal) , organic chemistry , atomic physics , cyclotron , physics , quantum mechanics , chromatography
The metastable dissociation of the methoxymethyl cation and a number of its deuterium and 13 C variants was examined using a reverse‐geometry double‐focusing mass spectrometer. The loss of methane from the methoxymethyl cation clearly showed a composite peak shape which, when deconvoluted, revealed a bimodal kinetic energy release distribution in the resulting formyl cations. Labelling experiments revealed that the two carbon atoms and all hydrogens become equivalent on the time‐scale of the unimolecular dissociation lifetime of the decomposing ion. A small deuterium isotope effect was found which can be rationalized on the basis of zero point energy effects. The bimodal kinetic energy release distribution was shown, with the aid of a four‐sector instrument, to be due to the production of both formyl cation (with a large kinetic energy release) and isoformyl cation (with a much smaller kinetic energy release). The methoxymethyl cation was also prepared with a precisely defined amount of internal energy in a Fourier transform ion cyclotron resonance (FTICR) spectrometer by the reaction of methyl cation with formaldehyde. Experiments with 13 C and deuterium labelling revealed that the dissociation to formyl cation of the methoxymethyl cations formed in the low‐pressure FTICR cell by reaction of methyl cation with formaldehyde is accompanied by complete scrambling of the carbons and incomplete scrambling of the hydrogens. Ab initio calculations were carried out which identified and characterized each of the stable minima and transition states for the appropriate reactions. The calculations were fully consistent with the mechanism deduced on the basis of the experimental data.