The UNIFAC group contribution method was used to calculate the infinite dilution activity coefficients (gamma(infinity)) of 2-chloro-2-methylpropane (t-BuCl) in the binary mixtures methanol/ethanol, methanol/2-methoxyethanol, and ethanol/2-methoxyethanol at 298.15 K. For each system, nine different compositions of the solvent mixtures were considered. The modified Flory-Huggins equation in the combinatorial term was used, as well as the group contribution parameters from the vapor-liquid equilibrium parameter table in the residual term, due to the nonavailability of specific gamma(infinity) UNIFAC interaction parameters for the relevant groups. The gamma(infinity) values were combined with a set of new and experimentally determined kinetic parameters of the solvolytic reactions of the same substrate in the same solvents to describe quantitatively the contributions of the initial state and the transition state to the solvent effect. By using this approach, the Gibbs energies of transfer of the reactants and the activated complex were obtained, which allows us to better understand the reaction mechanism and to influence reaction rates through a coherent selection of solvents.