Unimolecular Reactions of Ionized Methyl Acetate and Its Hydrogen-Rearranged Isomers

摘要

The proposed formation of (CH3C(OH)OCH2)(+) (b) as the intermediate in the isomerization CH2-C(OH)OCH3(+) double bond (a) yields b yields CH3C00CH3(+) reversible reaction (c) has been confirmed by preparation of b from CH3COOCH2OCH3. For the three isomers a-c the dominant metastable ion (MI) dissociation, CH30 loss, inolves identical kinetic energy release values. The kinetic barriers for a yields band b yields c must be nearly as high as that for CH30 loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a-c to ionizing electron energy. The H/D scrambling of metastable (CH2-C(OD)OCH3) double bond and c-D3 ions confirm this, indicating that the barrier for a yields b is reversible reaction slightly below that for b yields c. Minor low-energy dissociations include losses of CH4 and CH30H from a and losses of CHO and CH20 from b. Comparison of MI and CAD spectra of a-c with those from (CH3(OH)CH20)(+) (d) and (CH3COCH2OH(+) (e) give no evidence for skeletal rearrangement of a-c to d or e.