PMID: 11902887Mar 21, 2002Paper

Formation and stability of enolates of acetamide and acetate anion: an Eigen plot for proton transfer at alpha-carbonyl carbon

Journal of the American Chemical Society
John P RichardTina L Amyes

Abstract

Second-order rate constants were determined in D(2)O for deprotonation of acetamide, N,N-dimethylacetamide, and acetate anion by deuterioxide ion and for deprotonation of acetamide by quinuclidine. The values of k(B) = 4.8 x 10(-8) M(-1) s(-1) for deprotonation of acetamide by quinuclidine (pK(BH) = 11.5) and k(BH) = 2-5 x 10(9) M(-1) s(-1) for the encounter-limited reverse protonation of the enolate by protonated quinuclidine give pK(a)(C) = 28.4 for ionization of acetamide as a carbon acid. The limiting value of k(HOH) = 1 x 10(11) s(-1) for protonation of the enolate of acetate anion by solvent water and k(HO) = 3.5 x 10(-9) M(-1) s(-1) for deprotonation of acetate anion by HO(-) give pK(a)(C) approximately 33.5 for acetate anion. The change in the rate-limiting step from chemical proton transfer to solvent reorganization results in a downward break in the slope of the plot of log k(HO) against carbon acid pK(a) for deprotonation of a wide range of neutral alpha-carbonyl carbon acids by hydroxide ion, from -0.40 to -1.0. Good estimates are reported for the stabilization of the carbonyl group relative to the enol tautomer by electron donation from alpha-SEt, alpha-OMe, alpha-NH(2), and alpha-O(-) substituents. The alpha-NH(2)...Continue Reading

References

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Citations

Feb 15, 2007·Journal of the American Chemical Society·Krisztina Toth, John P Richard
Oct 1, 2009·Journal of the American Chemical Society·Wing-Yin Tsang, John P Richard
Aug 31, 2002·Organic Letters·Gonzalo CosaMiguel A Miranda
Jul 8, 2011·Pure and Applied Chemistry. Chimie Pure Et Appliquée·John P Richard
May 10, 2016·Journal of Chromatography. a·Man WangDavid Da Yong Chen
May 27, 2005·Organic & Biomolecular Chemistry·Juan CrugeirasJohn P Richard
Nov 12, 2019·Chemistry : a European Journal·Andrew BallardAndrew G Leach
Apr 1, 2020·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Remigiusz BąchorZbigniew Szewczuk
Oct 10, 2018·Organic & Biomolecular Chemistry·Joshua P BarhamYoshitaka Hamashima
Jan 22, 2014·Journal of Mass Spectrometry : JMS·Remigiusz BąchorZbigniew Szewczuk
Dec 1, 2010·Chemical Communications : Chem Comm·Eleanor M HigginsAnnMarie C O'Donoghue
Jul 26, 2006·The Journal of Physical Chemistry. a·Daqing GaoHughton Walker
Mar 27, 2010·Journal of the American Chemical Society·Junming HoMichelle L Coote
Apr 7, 2009·The Journal of Organic Chemistry·Anne-Gaelle CollotRory A More O'Ferrall
Feb 10, 2009·Journal of Chemical Theory and Computation·Junming Ho, Michelle L Coote
Jun 8, 2021·Chemical Science·Oliver R MaguireAnnMarie C O'Donoghue
Sep 19, 2012·The Journal of Physical Chemistry. B·Edgar MixcohaAngels González-Lafont
Sep 26, 2013·The Journal of Organic Chemistry·Dharmit MistryMichael I Page
Jul 11, 2002·Journal of the American Chemical Society·Ana RiosTina L Amyes
Aug 26, 2004·Journal of the American Chemical Society·Krisztina TothMáire E NíBeilliú

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