Nitrous Oxide in Gas-Phase Ion-Molecule Chemistry: A Versatile Reagent for the Determination of Carbanion Structure

Nitrous oxide has been found to undergo a wide variety of reactions with anions in the gas phase. The products of these reactions are highly characteristic of the ion’s structure and, therefore, this reagent (N₂0) is especially useful in distinguishing between different types of ions. In general, primary carbanions react to produce diazo anions as the major products, secondary carbanions dehydrogenate, and tertiary carbanions afford adducts, oxygen atom transfer, and cleavage products. However, novel reaction channels can be brought about by modifying the reactant ion’s structures. For example, deprotonation of methylene cyclopropane produces a strained allylic anion which reacts with N₂0 to afford cyanide and the 2-nitrosoallyl anion, while removal of a proton from furan, which has a good a-leaving group, generates the nitrogen atom transfer product, 3-cyanoacrolein radical anion, upon reaction with N₂0. It was observed that proton abstraction from cyclopentene, cyclohexene, and internal olefins without allylic methyl groups does not afford M - 1 ions in the flowing afterglow.