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KMID : 1059519910350030196
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Journal of the Korean Chemical Society
1991 Volume.35 No. 3 p.196 ~ p.203
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Studies on the Dissociation Constant of Benzoic Acid and Substituted Benzoic Acids in Methanol-Water Mixtures by Conductometric Method
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Cho Min-Soo
Park Hyoung-Ryun
Lee Soon-Ki
Lee Kye-Soo
Lee Bon-Su
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Abstract
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The pKa values of benzoic acid and meta, para-halogen substituted benzoic acids in MeOH-H2O mixtures (0∼80% of MeOH) have been determined at 25℃ using a conductometric method on the basis of the Fuoss-Kraus equation, and further verified using modified conductometric method of Gelb. The dependence of pKa on halogen substituents has been discussed in terms of substituent-constant (σ), which is devided into electron-withdrawing inductive contribution (σI) and electron-donating π-resonance one (σR). The linear-dependence of σI's on D-1 with positive slope and that of σR's on D-1 with negative slope have been interpreted on the basis of field effect and through-space interaction of π-lone pair of halogen substituent and ionization center via π-system of benzene ring.
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