Alkylation of Enolate Ions

We describe a procedure for studying gas-phase ion-molecule chemistry in which the neutral reaction products are collected and identified. Our experiment uses a flowing afterglow device configured with a cryogenic trapping column; material collected on this column is separated by capillary chromatography and the individual components are identified by their retention time and their electron impact mass spectrum. We have used this device to study the reaction of the cyclohexanone enolate ion with CH₃Br. We find that reaction of this enolate proceeds with a rate constant of 3.9 X 10^-10 cm³ molecule^-1 s^-1 to produce only the product resulting from O-alkylation, 1-methoxycyclohexene; there is no evidence for the product resulting from C-alkylation.