Carbonium Ions. X. Hydride Transfers Involving Arylcarbonium and Alkylcarbonium Ions

Solution carbocation stabilities measured by internal competition for a hydride ion

“…Furthermore, much information relating to relative carbocation stabilities is available from a host of other techniques, such as solvolysis rate comparisons, calorimetry of ionization processes (2), mass spectrometry and ion cyclotron resonance (3) (reaction [2]-type gasphase equilibria are now accurately known for a large number of systems), pKa-type equilibria (4), kinetics of various acid-catalyzed reactions, >AA; / \ Not only are these equilibria very hard to measure (6) (because of polymerization) but we believe that one must take account of more steric factors in this case. Although many studies involving [2]-type reactions have appeared in the past, they have focussed primarily on kinetics (7) or synthetic applications, the numerical equilibrium constant being of secondary concern. However, Kramer and co-workers have reported some studies devoted entirely to measuhng [2]-type equilibria (8) A serious drawback to intermolecular equilibria involves experimental difficulties associated with an oxidation of the hydrocarbon component (9) of these equilibria by the excess strong acid solvent system used in generating the cation component, leading to "messy" nmr spectra.…”