Unimolecular reactions of ionized methyl acetate and its hydrogen‐rearranged isomers

The proposed formation of [CH 3 C(OH)OCH 2 ] + ˙ ( b ) as the intermediate in the isomerization [CH 2 C(OH)OCH 3 ] + ˙ ( c )⇄ b ⇄[CH 3 COOCH 3 ] + ˙ ( c has been confirmed by preparation of b from CH 3 COOCH 2 OCH 3 . For the three isomers a–c the dominant metastable ion (MI) dissociation, CH 3 O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a ⇄ b and b ⇄ c must be nearly as high as that for CH 3 O˙ 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 [CH 2 C(OD)OCH 3 ] + ˙ and c –D 3 ions confirm this, indicating that the barrier for a ⇄ b is slightly below that for b ⇄ c . Minor low‐energy dissociations include losses of CH 4 and CH 3 OH from a and losses of ˙CHO and CH 2 O from b . Comparison of MI and CAD spectra of a–c with those from [CH 3 (OH)CH 2 O] + ˙ ( d ) and [CH 3 COCH 2 OH] + ˙ ( e ) give no evidence for skeletal rearrangement of a–c to d or e .