ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 35, Number 3
JKCSEZ 35(3)
June 20, 1991 

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.