The unimolecular metastable decompositions of ethoxytrimethylsilane ((CH
3)
3SiOCH
2CH
3; 1, MW: 118) and its fluorine analogue, 2,2,2-trifluoroethoxytrimethylsilane ((CH
3)
3SiOCH
2CF
3, 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
+ · is different from that of 2
+ · , except for the loss of CH
3 from the corresponding molecular ions. The MIKE spectra of the [M - CH
3]
+ ions from 1
+ · and 2
+ · 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, (CH
3)
2Si
+OCH = CH
2, and
m/z 61, CH
3Si
+HOH, concern new mechanistic pathways, which were not described in previous reports. Skeletal rearrangement by among others F and CF
3 migrations, occurs during the fragmentation of the [M - CH
3]
+ ions from 2
+ · . The
m/z 61 ions from 2
+ · are both CH
2OCF
+ (or CH
2FCO
+ etc.) and CH
3Si
+HOH.
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