Rationalization of scrambling processes among [C 2 H 3 O] + ions

Scrambling data for the three observed [C 2 H 3 O] + isomers, namely [CH 3 CO] + ( a ), [CH 2 COH] + ( b ) and ( c ), are rationalized by using ab initio molecular orbital calculations. For ions a and c , processes leading to scrambling of the carbon atoms require substantially more energy than the threshold for decomposition to [CH 3 ] + + CO. Accordingly, little or no carbon scrambling is predicted nor is any observed in the metastable dissociation of a and c . The observed carbon scrambling in b prior to metastable dissociation to [CH 3 ] + + CO has previously been explained in terms of a mechanism involving the oxiranyl cation ( c ). However, this mechanism is shown to be unlikely because of the high energies involved. An alternative lower‐energy pathway involving the intermediacy of protonated oxirene ( h ) is proposed. Such a mechanism is fully compatible with the experimental data.