The Origin of the α-Effect: Dissection of Ground-State and Transition-State Contributions
- 29 December 1999
- journal article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 65 (2) , 577-582
- https://doi.org/10.1021/jo9915776
Abstract
The origin of the α-effect has been probed through a combination of calorimetric and kinetic studies involving butane-2,3-dione monoximate as α-nucleophile and p-chlorophenoxide as normal nucleophile in the reaction with p-nitrophenyl acetate in DMSO−H2O mixtures, which has been shown to exhibit a bell-shaped profile in the α-effect with solvent composition. The study, involving determination of enthalpies of solution and activation parameters, has allowed a dissection of contributions to the α-effect of ground-state destabilization and transition-state stabilization in these DMSO−H2O solvent media. It has been found that over the solvent composition 0−50 mol % DMSO desolvation of the α-nucleophile is the main driving factor to the increasing α-effect. However, in solvent mixtures covering 50−90 mol % DMSO the thermodynamic activation parameters suggest an interplay of factors that result in the bell-shaped α-effect profile. Discussion is presented that includes possible medium-dependent nonsynchronicity of nucleophile desolvation and bond formation for the α-nucleophile.Keywords
This publication has 39 references indexed in Scilit:
- Effect of Solvent on the α-Effect: Nucleophilic Substitution Reactions of p-Nitrophenyl Acetate with m-Chlorophenoxide and Benzohydroxamates in MeCN−H2O Mixtures of Varying CompositionsThe Journal of Organic Chemistry, 1997
- Evidence That the α-Effects in Methyl Transfers from Aryldimethylsulfonium Salts Correlate with Single-Electron-Transfer CharacteristicsThe Journal of Organic Chemistry, 1997
- α-Effect with Substituted N-Methylbenzohydroxamates and Substituted Phenyldimethylsulfonium Salts: Toward Understanding of an Intrinsic α-EffectThe Journal of Organic Chemistry, 1997
- Nucleophiles of high reactivity in phosphoryl transfer reactions: .alpha.-effect compounds and fluoride ionJournal of the American Chemical Society, 1990
- Hydrogen exchange studies. X. Base-catalyzed isotopic exchange of molecular hydrogen. III. Transition-state vs. initial-state solvation in the dimethyl sulfoxide-water systemJournal of the American Chemical Society, 1976
- Ultrasound propagation in binary mixtures of dimethyl sulfoxide and waterThe Journal of Physical Chemistry, 1974
- Transition state enthalpies of transfer in aqueous dimethyl sulfoxide solutions. Alkaline hydrolysis of ethyl acetateThe Journal of Physical Chemistry, 1974
- Some Thermodynamic Properties of the Dimethylsulfoxide–Water and Propylene Carbonate–Water Systems at 25 °CCanadian Journal of Chemistry, 1974
- Solvent Effects in Organic Chemistry. V. Molecules, Ions, and Transition States in Aqueous Ethanol1Journal of the American Chemical Society, 1965
- The Factors Determining Nucleophilic ReactivitiesJournal of the American Chemical Society, 1962