Kinetics and mechanism of unimolecular heterolysis of cage-like compounds: XXI. Solvent effect on the realtive rate of heterolysis of 2-methyland 2-phenyl-2-haloadamantanes. Role of activation parameters

The kinetics of heterolysis of 2-chloro-2-methyladamantane, 2-bromo-2-methyladamantane, 2-chloro-2-phenyladamantane, and 2-bromo-2-phenyladamantane in isopropyl alcohol, tert-butyl alcohol, acetonitrile, nitromethane, cyclohexanone, and γ-butyrolactone were studied using the verdazyl technique. The rate constant ratio k Ph/k Me decreases from three orders of magnitude to unity in the solvent series BuOH > i-PrOH > t-BuOH > MeCN > PhNO₂ > cyclohexanone > γ-butyrolactone > sulfolane, which results from weakening of conjugation between the phenyl group and emerging carbocationic center. The effect of solvent on the entropy and enthalpy of heterolysis in going from 2-methyl-substituted 2-haloadamantanes to their 2-phenyl analogs is discussed.