Termodynamics and Kinetics of Carbon-Carbon Bond Formation and Heterolysis Through Reactions of Carbocations with Carbanions in Solution

Article abstract of DOI:10.1021/j100275a005

Rate data are presented for the heterolysis of carbon-carbon bonds and their formation through coordination of resonance-stabilized carbocations and carbanions in acetonitrile solution at 25 deg C.These rates were determined by NMR line broadening and by the T jump technique (in a solution containing 0.48 M supporting electrolyte).Preliminary results are given for a "master equation" to predict some heterolysis energies in solution as a complement to Benson's method for homolysis energies.The results provide for the first time an opportunity to compare the effects of structure variation on the kinetic and thermodynamic properties for such an ostensibly simple reaction in solution.All evidence so far accumulated indicates that these reactions are dominated by ion-solvation factors so that they have little bearing on the gas-phase heterolysis energies.Ionic strength effects and substituent variation suggest that charge development is about half developed at the transition state, but we argue that this cannot be translated simply into pictures of transition-state structure.The results provide a flagrant reversal of the frequently invoked "reactivity selectivity principle" since the most reactive cation is also most selective.On the basis of these results and many others which have appeared recently it may be appropriate to discard the reactivity selectivity principle as a useful principle for either prediction or interpretation.