Keto and enol forms of methyl acetate molecular ions,their stability and interconvertibility prior to fragmentation in the gas phase

The heats of formation of the keto and enol forms of the molecular ion of methyl acetate are 577 ± 4kJ mol^?1 and 477 ± 4KJ mol^?1 respectively. Fragmentation by loss of CH₃O˙ takes place at the thermochemical threshold for [CH₃CO]⁺ formation for both isomers, which may therefore freely interconvert at internal energies corresponding to this decomposition threshold.