Kinetic Studies of Intermolecular Hydrogen Bonding in Carboxylic Acids by Means of Ultrasonic Absorption Measurement. II. Halogeno Carboxylic Acids

概要

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The ultrasonic absorptions in several halogeno carboxylic acids, such as monochloroacetic, dichloroacetic, trichloroacetic, trifluoroacetic, α-chloropropionic, and β-chloropropionic acids, have been measured in the frequency range from 2.5 to 95 MHz. Excess absorptions were observed in all the acids. The kinetic and the thermodynamic parameters based on the equilibrium between the open dimer and the cyclic dimer were calculated. An application of Taft's equation, logK=ρ*σ*+sEs, to the results suggests that neither the equilibrium constant nor the rate constant depends on the polarity effect of the alkyl group, but depends mainly on the steric effect, and that the reaction is controlled not only by the enthalpy change, but also by the entropy change.
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