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.