Measuring Structural and Electronic Effects on Keto–Enol Equilibrium in 1,3-Dicarbonyl Compounds

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• 作者：Kyle T. Smith ; Sherri C. Young ; James W. DeBlasio ; Christian S. Hamann
• 刊名：Journal of Chemical Education
• 出版年：2016
• 出版时间：April 12, 2016
• 年：2016
• 卷：93
• 期：4
• 页码：790-794
• 全文大小：251K
• 年卷期：0
• ISSN：1938-1328

文摘

Nuclear magnetic resonance (NMR) spectroscopy is an integral part of the undergraduate chemistry curriculum. In addition to structure determination, NMR spectroscopy is used to analyze chemical reactions and equilibria in situ. Determination of the position of equilibria is well-suited to NMR analysis in the undergraduate laboratory as an extension of peak identification and signal integration, and the determination of keto–enol equilibrium remains a popular undergraduate laboratory experiment. Several factors affect the position of keto–enol equilibrium, defined here as K_e/k = [enol]/[keto], including structure (steric bulk, conjugation, electron-withdrawing/donating groups, resonance), temperature, and solvent. A judiciously selected set of compounds that have a common 1,3-dicarbonyl moiety with progressively changing ligands at the 1 and 3 positions is presented. This array allows students to investigate structure–function relationships that affect keto–enol equilibrium in a cumulative fashion and affords instructors a broad selection of compounds for study in both introductory and advanced laboratory courses using a variety of pedagogic approaches.