Metastable decomposition of C3H6O+? ions

The metastable enol isomer (1) of the acetone ion probably ketonizes and then loses methyl in the mass spectrometer. We report here that ionized acetone (2) loses methane instead of methyl upon metastable decomposition. The metastable losses of methyl and methane starting from (1) and (2) differ in relative rate by > 104, apparently due to excess internal energy in the keto-ions generated by isomerization. C3H6O+˙ ions with the oxygen on the first carbon lose a hydrogen atom rather than methyl or methane. Thus, metastable C3H6O+˙ ions with the oxygen on the first carbon do not rearrange to their isomers with the oxygen on the second carbon, in contrast to C4H8O+˙ ions.