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  Home > JCE Print > Journal of Chemical Education > Issues > 2007  > November  >
In the Laboratory
Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR
Revisiting a Classic Physical Chemistry Experiment
A. Gilbert Cook and Paul M. Feltman
Department of Chemistry, Valparaiso University, Valparaiso, IN 46383
Cover
November 2007
Vol. 84 No. 11
p. 1827

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.
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Description of the student experiment and notes for the instructor are available.
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Citation
Cook, A. Gilbert; Feltman, Paul M. J. Chem. Educ. 2007, 84, 1827.
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Keywords
Aldehydes / Ketones; Equilibrium; Hands-On Learning / Manipulatives; Hydrogen Bonding; Laboratory Instruction; Molecular Modeling; Molecular Properties / Structure; NMR Spectroscopy; Organic Chemistry; Physical Chemistry; Second-Year Undergraduate; Solutions / Solvents; Thermodynamics; Upper-Division Undergraduate
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History
Created:
Last Updated:
9/19/2007
10/9/2007
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Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
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