Free Cyclohexyl Cations From the Decay of Tritiated Cyclohexane

The existence, stability, and isomerization rate of free, unstabilized cyclohexyl cation are addressed by using the decay technique. Labeled cyclohexyl ions, unsolvated and free of counterions, are generated in gaseous and liq. systems by the decay of a constituent atom of multitritiated cyclohexane. The daughter ions possess up to ∼30 kcal mol-1 excess internal energy, being formed in a geometry reminescent of the neutral parent, rather than in the most stable structure of the cyclohexyl cation. The anal. of the tritiated products from the reaction of the decay ions with suitable nucleophiles in different environments provides compelling evidence for the existence of free cyclohexyl ion as a legitimate intermediate having a lifetime of at least 10-8-10-7 s. The cation corresponds to a local min. on the C6H11+ energy surface, whose depth, deduced from the rate of isomerization to the more stable 1-methylcyclopentyl structure, is estd. to be <10 kcal mol-1. The results confirm earlier conclusions from a radiolytic study and provide useful information on the relative reaction rate of free cyclohexyl and 1-methylcyclopentyl cations toward several nucleophiles.