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Corral‐Bautista, Francisco; Appel, Roland; Frickel, Johanna S.; Mayr, Herbert

Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

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  • Medientyp: E-Artikel
  • Titel: Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide
  • Beteiligte: Corral‐Bautista, Francisco; Appel, Roland; Frickel, Johanna S.; Mayr, Herbert
  • Erschienen: Wiley, 2015
  • Erschienen in: Chemistry – A European Journal, 21 (2015) 2, Seite 875-884
  • Sprache: Englisch
  • DOI: 10.1002/chem.201404500
  • ISSN: 0947-6539; 1521-3765
  • Entstehung:
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  • Beschreibung: <jats:title>Abstract</jats:title><jats:p>Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCOCH<jats:sup>−</jats:sup>Acc) and benzyl anions (PhCH<jats:sup>−</jats:sup>Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10<jats:sup>−2</jats:sup> mol L<jats:sup>−1</jats:sup>), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K<jats:sup>+</jats:sup> did not have any influence on the rate constants at carbanion concentrations in the range of 10<jats:sup>−4</jats:sup>–10<jats:sup>−3</jats:sup> mol L<jats:sup>−1</jats:sup>, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K<jats:sup>+</jats:sup>&lt;Na<jats:sup>+</jats:sup>&lt;Li<jats:sup>+</jats:sup>, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters <jats:italic>N</jats:italic> and <jats:italic>s</jats:italic><jats:sub>N</jats:sub> of the free carbanions were derived from the linear plots of log <jats:italic>k</jats:italic><jats:sub>2</jats:sub> against the electrophilicity parameters <jats:italic>E</jats:italic> of the reference electrophiles, according to the linear‐free energy relationship log <jats:italic>k</jats:italic><jats:sub>2</jats:sub>(20 °C)=<jats:italic>s</jats:italic><jats:sub>N</jats:sub>(<jats:italic>N</jats:italic>+<jats:italic>E</jats:italic>). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known <jats:italic>E</jats:italic> parameters.</jats:p>