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- Title
New Approach to Analysis of the Nonlinearity of the Brønsted Relationship: II. An Empirical Procedure Combining the σρ Correlation Method with the Concept of Hard and Soft Acids and Bases, as Applied to Pseudo CH Acids.
- Authors
Tupitsyn, I. F.
- Abstract
A comparative systematic σρ analysis of the features of Brönsted behavior of pseudo CH acids(according to Eigen's classification) is made. The analysis is based on combined use of experimental data onpKa, ΔGgas, logkD of CH acids (ΔGgas is the free energy of acid ionization in the gas phase, logkD isthe logarithm of the rate constant of hydrogen exchange in a protic solvent). The modified nucleophilicKabachnik constants σ- are applicable to σρ correlations for all the three kinds of acidity of pseudo CH acids. The electrostatic solvation makes an insignificant contribution to variation of pKa and weakening of the substituent effect in going from the gas phase to dimethyl sulfoxide, and also to differentiation of the kinetic acidity. The coefficient α in the Brönsted equation and the ratio between the rate constants ρ in the σρ correlations, which characterize the degree of proton transfer in the reaction transition state, have much in common from the physical viewpoint. The results of σρ correlation analysis, demonstrating intramolecular uniformity of the interactions, are fully consistent with the conclusion made in the previous part of this work about the solvation uniformity of the interactions, resulting in the absence of thermodynamic deviations from the Brönsted relationship.
- Subjects
ACIDS; PROTON transfer reactions; CHARGE transfer; CHEMICAL reactions; CHEMISTRY; PHYSICAL sciences
- Publication
Russian Journal of General Chemistry, 2004, Vol 74, Issue 2, p179
- ISSN
1070-3632
- Publication type
Article
- DOI
10.1023/B:RUGC.0000025497.22963.5d