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Title:A Quantitative Analysis of Solvent Effects on Keto-Enol Tautomeric Equilibria
Author(s):Mills, Sander Gilbert
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Organic
Abstract:Solvent dependent tautomeric equilibria of dimedone, 2-methyl-1,3-cyclohexanedione, anthrone, acetylacetone, ethyl acetoacetate and 3-oxabicyclo{4.3.0}-2,9-dioxononane, representative of the major classes of (beta)-dicarbonyl and phenolic tautomeric equilibria, are determined in a variety of solvents by high dilution FT NMR and UV studies. O-Methylated enol ethers are used as models for the ultraviolet chromophores of dimedone and 2-methyl-1,3-cyclohexanedione, and a comparison is made to NMR results on these systems. Temperature studies are performed to examine trends in (DELTA)H('0) and (DELTA)S('0) in the different systems.
Of the several empirical and theoretical models tested against the data sets, the Kamlet-Taft parameters (pi)*, (alpha), and (beta) give the best correlation overall, although Swain's recently introduced solvent polarity parameter A + B was most successful at correlating the acetylacetone and ethyl acetoacetate data. Based on the correlation results, two distinct categories of solvent sensitivity are observed, depending exclusively on whether or not the compound has an internal hydrogen bond. For these species without internal hydrogen bonds, the equilibria are controlled almost completely by the hydrogen bond basicity of the solvent. For compounds with intramolecular hydrogen bonds, solvent polarity/polarizability dominates, though hydrogen bonding effects remain important. Quantitative comparison among parameters indicative of the dominant interactions for each case are given and methods for generalizing these results are suggested.
Thermodynamic data are analyzed to show that neither potential nor kinetic energy effects are separately responsible for the observed solvent sensitivity of acetylacetone, and it is suggested that dominance of either of these terms in unlikely for compounds whose equilibria are controlled by the effects described above.
Issue Date:1983
Description:189 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
Other Identifier(s):(UMI)AAI8410000
Date Available in IDEALS:2014-12-15
Date Deposited:1983

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