Unimolecular Decompositions of 2,2,2-Trifluoroethyl Acetate, 2,2,2-Trifluoroethyl Trifluoroacetate, and S-Ethyl Trifluorothioacetate upon Electron Impact

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The unimolecular decompositions of the metastable ions produced from 2,2,2-trifluoroethyl acetate, CH₃COOCH₂CF₃, 1, (M_w: 142), 2,2,2-trifluoroethyl trifluoroacetate, CF₃COOCH₂CF₃, 2, (M_w: 196), and S-ethyl trifluorothioacetate, CF₃COSCH₂CH₃, 3, (M_w: 158) upon electron ionization have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. The metastable ions 1⁺ decompose exclusively to give the ion at m/z 122 by losing HF via an 1,2-elimination.
In the normal mass spectrum of 2, no molecular ion is observed, while the ion corresponding to the loss of CF₃ gives rise to an intense peak at m/z 127 (about 90% of the base peak) and the ion corresponding to the loss of F gives the peak at m/z 177 with moderate intensity (about 20%). Both ions consist of two isomeric ions. Some interesting rearrangement processes, such as CF₃ or OCH₂CF₃ migration followed by the loss of a CO molecule, occur during the metastable fragmentations of these ions.
The molecular ion of 3, which is a base peak, decomposes into the ions at m/z 89 and 61 by losing CF₃ and CF₃CO, respectively, in the metastable time region. The relative abundance of ions in the MIKE spectrum are rationalized with the thermochemical data estimated by the PM 3 method.