Essentially Solvent-Independent Rates of Solvolysis of the 1-Adamantyldimethylsulfonium Ion. Implications Regarding Nucleophilic Assistance in Solvolyses of tert-Butyl Derivatives and the NKL Solvent Nucleophilicity Scale

Article abstract of DOI:10.1021/ja00267a030

Rearside nucleophilic solvation of the developing carbocation is severely hindered during the solvolysis of the 1-adamantyldimethylsulfonium ion (1-AdSMe2⁺).For variation in the composition of binary solvent systems, the ion always shows a variation of the specific rate in the opposite direction to that observed for the tert-butyldimethylsulfonium ion (t-BuSMe2⁺); these observations are rationalized in terms of a dominanat nucleophilic solvation at the transition state for t-BuSMe2⁺ solvolysis and a dominanat nucleophilic stabilization of the reactant for 1-AdSMe2⁺ solvolysis.These systems are compared to the corresponding alkyl halides.Corrections applied in setting up the N_Kl scale of solvent nucleophilicities would be better based on 1-AdSMe2⁺ solvolyse.However, the intensitivity of 1-AdSMe2⁺ solvolyses to solvent variation (specific rates in 41 solventa, at 70.4 deg C, vary by less than a factor of seven) allows log (k/ko)_Et3O+ values to be taken as a good measure of solvent nucleophilicity.For solvolyses of 1-AdSMe2⁺ in aqueous ethanol (ca. 60percent ethanol), the S value (favoring reaction with water) is 1.35 at both 70.6 and 100.1 deg C.