Temperature dependence of the rate and activation parameters for tert-butyl chloride solvolysis: Monte Carlo simulation of confidence intervals

The solvolysis rate constants (kobs) of tert-butyl chloride are measured in 20%(v/v) 2-PrOH–H2O mixture at 15 temperatures ranging from 0 to 39 °C. Examination of the temperature dependence of the rate constants by the weighted least squares fitting to two to four terms equations has led to the three-term form, lnkobs=a1+a2T−1+a3lnT, as the best expression. The activation parameters, ΔH‡ and ΔS‡, calculated by using three constants a1, a2 and a3 revealed the steady decrease of ≈1 kJ mol−1 per degree and 3.5 J K−1 mol−1 per degree, respectively, as the temperature rises. The sign change of ΔS‡ at ≈20.0 °C and the large negative heat capacity of activation, ΔCp‡=−1020 J K−1 mol−1, derived are interpreted to indicate an SN1 mechanism and a net change from water structure breaking to electrostrictive solvation due to the partially ionic transition state. Confidence intervals estimated by the Monte Carlo method are far more precise than those by the conventional method.