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Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR

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A. Gilbert Cook and Paul M. Feltman

Department of Chemistry, Valparaiso University, Valparaiso, IN 46383

J. Chem. Educ., 2007, 84 (11), p 1827

DOI: 10.1021/ed084p1827

Publication Date (Web): November 1, 2007

Section:

History, Education, and Documentation

Abstract

The use of proton NMR to determine the equilibrium position of tautomeric 1,3-dicarbonyl compounds in various solvents has been a classic physical chemistry experiment. We are presenting an expansion of the excellent description of this experiment by Garland, Shoemaker, and Nibler. Often the assumption is made that the keto tautomer is always the more polar tautomer and hence the concentration of the keto tautomer is greater in polar solvents. However, the keto tautomers of acyclic 1,3-dicarbonyl molecules such as acetyl acetone are often not the more polar of the two tautomers, so this cannot be the only important factor that determines this equilibrium. Rather there are several factors that contribute to the tautomeric equilibrium of which solute dipole moment is just one. The study of the cyclic 1,3-diketone dimedone is especially helpful in this regard. The student is asked to analyze his/her results based on these factors. Molecular modeling is used as an aid in this analysis.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Organic Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Aldehydes / Ketones

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This article has been cited by 2 ACS Journal articles (2 most recent appear below).

Substituent Effects on Keto–Enol Equilibria Using NMR Spectroscopy
Kimberly A. Manbeck, Nicholas C. Boaz, Nathaniel C. Bair, Allix M. S. Sanders, and Anderson L. Marsh
Journal of Chemical Education2011 Article ASAP
- Substituent Effects on Keto–Enol Equilibria Using NMR Spectroscopy
  Kimberly A. Manbeck, Nicholas C. Boaz, Nathaniel C. Bair, Allix M. S. Sanders, and Anderson L. Marsh
  Journal of Chemical Education2011 Article ASAP
  In this extension to a classic physical chemistry experiment, students record the proton nuclear magnetic resonance spectra of the β-diketones 2,4-pentanedione, 3-methyl-2,4-pentanedione, and 3-chloro-2,4-pentanedione to investigate the effect of ...
  Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto−Enol Tautomeric Equilibrium Reactions
Michael A. Nichols and Mark J. Waner
Journal of Chemical Education2010 87 (9), 952-955
- Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto−Enol Tautomeric Equilibrium Reactions
  Michael A. Nichols and Mark J. Waner
  Journal of Chemical Education2010 87 (9), 952-955
  An extension of the classic keto−enol tautomerization of β-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the α-methylene ...
  Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links