Solvolysis of 2-Aryl-2-chloro-4,4-dimethylpentanes. Confirmation of Validity of Brown−Okamoto σ+Constants

Abstract

Specific rate constants of solvolysis in 90% aqueous acetone have been determined at 25 °C for 10 2-aryl-2-chloro-4,4-dimethylpentanes (3) having a substituent p-cycPr, p-Me, m-Me, p-F, (H), p-Cl, m-Cl, m-CF3, p-CF3, or p-NO2. The Hammett−Brown relation is satisfactorily linear (r = 0.999) with ρ+ of −4.51, showing that Brown−Okamoto σ+ values based on the solvolysis of the cumyl chloride system 1 are widely usable for the substrates solvolyzing without appreciable nucleophilic solvent participation. Solvolysis of 3 having 3,5-Cl2 or 3,5-(CF3)2 substituents suggests the use of σ+ values of +0.740 and +0.982 instead of respective 2σm+ values of +0.798 and +1.040. The large negative ρ+ values in TFE of −5.91 and −5.63 for 1 and 3, respectively, reflect decreased nucleophilic (or Bronsted base type) solvation. Comparison of solvolysis rates of 1 with 3, both having m-Cl, p-CF3, or 3,5-(CF3)2 substituents, in aqueous ethanol, aqueous acetone, TFE, and TFE−EtOH suggests that nucleophilic intervention by solven...