The unimolecular metastable decompositions of ethoxytrimethylsilane ((CH3)3SiOCH2CH3; 1, MW: 118) and its fluorine analogue, 2,2,2-trifluoroethoxytrimethylsilane ((CH3)3SiOCH2CF3, 2; MW: 172) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. Both molecular ions are formed in low abundance. The fragmentation of 1 ῌῌ is di#erent from that of 2 ῌῌ , except for the loss of CH3 from the corresponding molecular ions. The MIKE spectra of the [M῍CH3]ῌ ions from 1 ῌῌ and 2 ῌῌ gave five and three fragment ions, respectively. Two of the five reactions for 1 leading to the formation of the ion at m/z 101, (CH3)2Siῌ OCH῎CH2, and m/z 61, CH3Si ῌ HOH, concern new mechanistic pathways, which were not described in previous reports. Skeletal rearrangement by among others F and CF3 migrations, occurs during the fragmentation of the [M῍CH3] ῌ ions from 2 ῌῌ . The m/z 61 ions from 2 ῌῌ are both CH2OCF ῌ (or CH2FCO ῌ etc.) and CH3Si ῌ HOH.
The characterization and metastable decomposition of isobaric ions from several compounds are described by using high-resolution mass spectrometry (HR-MS) and mass-analyzed ion kinetic energy (MIKE) spectrometry. The m/z 45 ions from 2-methoxyethylamine, CH3OCH2CH2NH2 (1) consists of two isobaric ions, methoxymethyl ion, CH3OCH2ῌ , and C2H7N ῌ ion. The former decomposes into the m/z 29 ion by losing CH4 in metastable time window. Although the latter decomposes into the m/z 30 and 18 ions, its structure could not be confirmed in this study. The m/z 69 ions generated from methyl trifluoroacetoacetate, CF3COCH2COOCH3 (2) and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, CF3COCH2COCF3 (3) also consists of two isobaric ions, trifluoromethyl ion, CF3ῌ , and protonated carbon suboxide, OCCHCO ῌ . The former does not decompose into any ions in the metastable time window. On the other hand, the latter decomposes into m/z 41 ion by losing CO.
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