Substituent Effects on Keto–Enol Equilibria Using NMR Spectroscopy

Kimberly A. Manbeck ^[1] ; Nicholas C. Boaz ^[1] ; Nathaniel C. Bair ^[1] ; Allix M. S. Sanders ^[1] ; Anderson L. Marsh ^[1]
1. [1] Lebanon Valley College
  
  Lebanon Valley College
  
  Township of Annville, Estados Unidos
Localización: Journal of chemical education, ISSN 0021-9584, Vol. 88, Nº 10, 2011, págs. 1444-1445
Idioma: inglés
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Resumen
- 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 substituents on keto–enol tautomerization equilibria. From the integrated intensities of keto and enol methyl proton peaks, students calculate the equilibrium constant for each 2,4-pentanedione. The students then use the effects of electron-donating and electron-withdrawing substituents to elucidate the nature of keto–enol equilibria.