The gas-phase reactions of the methoxymethyl cation with aldehydes and ketones

The results of both mass-analysed ion kinetic energy spectroscopy and Fouri er transform ion cyclotron resonance experiments involving reactions of the methoxymethyl cation CH3OCH2+ with a variety of aldehydes and ketones are reported. With ketones, the reaction yields a covalent complex whose dissoc iation either gives back the CH3OCH2+ cation or leads to a methyl cation tr ansfer to the ketone. Except for CH2O, a third pathway is open with aldehyd es. A hydride transfer to CH3OCH2+ fields a RCO+ acylium product ion. The b ranching ratio of these three pathways strongly depends on the structure of the aldehyde. Ab initio calculations confirm that the results can be expla ined by the interconversion of covalent structures and electrostatic comple xes on the potential energy surface.