Selectivity of Stabilized Benzhydrylium Ions
Methyl carbonates (1―4―OCO 2 Me) and phenyl carbonates (2―4―OCO 2 Ph) were subjected to solvolysis in the series of aqueous ethanol, the product ratios were determined and the selectivities (k E /k W ) of the corresponding stabilized benzhydrylium ions 1―4 were calculated. The individual rate constants for ethanolysis (k E ) and hydrolysis (k W ) have been calculated. Ethanolysis proceeds via earlier more carbocation-like transition state than hydrolysis. Due to more important solvation, k E decreases slower than k W if the fraction of the water in the binary solvent increases, which net effect is pronounced dependence of the selectivity on the solvent polarity. The selectivities of less stable carbocations 5-8 are reduced and influenced by the leaving group because of pairing and bending of the log k vs. E plot.