Correlation analysis of solvent effects on solvolysis rates: What can the empirical parameters of solvents actually say?
Résumé
The logarithm of heterolysis rates of 4‐methoxyneophyl tosylate, Et3CBr, tert‐BuCl, and tert‐BuBr in a set of 12 to 28 hydrogen‐bond (HB) and non‐HB donor solvents are correlated to four sets of solvent parameters: (a) ET(30), (b) π*, α, β, (c) SP, SdP, SA, SB, and (d) DI, ES, α1, β1. Disjointed results are found for Et3CBr because of an insufficient diversity of solvents. For the other solvolyses, the determination coefficients r2 are good to excellent, the gas‐phase values are fairly predicted, and the contributions of various intermolecular forces to the global solvent effect agree satisfactorily within the four solvent sets. However, the most complete description of the solvent effect is given by the four‐parameter sets because their parameters refer to a single intermolecular force, whereas ET(30) and π*correspond to a fixed blend of solute/solvent interactions. For the application of the DI, ES, α1, and β1 set to correlate tert‐BuCl solvolysis, r2 = .976, lg k (gas) = −18.6 (experimental −19.3), and the contributions of HB donation (α1), electrostatic forces (ES), and dispersion‐induction (DI) to the solvent effect amounts to 59%, 21%, and 14%, respectively. The dependence of rates on the solvent HB basicity is nearly zero. The inclusion of the solvent cohesive energy density parameter urn:x-wiley:08943230:media:poc4067:poc4067-math-0001 into the correlation equations does not improve these correlations.
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Revised Correlation analysis of solvent effects on rate constants-JL-3.pdf (495.31 Ko)
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