Transmission of Substituent Effects through Oxygen and Sulfur Atoms. III. The Ionization Equilibrium Constants of Ring-substituted <i>cis</i>-β-Phenoxyacrylic Acids

Abstract

Abstract cis-β-Phenoxyacrylic acid and several of its ring-substituted derivatives were prepared, and their ionization constants were determined in 50% ethanol–water at 25 °C. The Hammett ρ value for the ionization of these acids, 0.439, is smaller than that reported for cis-β-phenylthioacrylic acids, 0.531. The greater efficiency of the sulfur atom in transmitting the substituent effects is explainable in terms of the “through-conjugation” of the sulfur atom in the thioacrylate anions formed.