ADDITIVE SUBSTITUENT EFFECTS ON IONIZATION OF META-SUBSTITUTED PHENOLS

Thermodynamic ionization constants of 3-ethoxyphenol; 3, 5-diethoxyphenol, 3, 5-dichlorophenol, 3, 5-dibromophenol, 3, 5-diiodophenol, and 3, 5-dinitrophenol have been measured spectrophotometrically within the temperature range 5-60°, and the thermodynamic functions of ionization ΔG25, ΔH25, ΔS25, and ΔCp.25 calculated. These results, in conjunction with others measured previously, indicate that, for this reaction series, substituent effects on the free energies of ionization are precisely additive, and on the entropies of ionization closely additive. An assessment of the results in terms of Hepler’s internal/external enthalpy theory is made. © 1968 CSIRO. All rights reserved.