Structural effects on the acidity of E‐α‐phenyl‐β‐arylacrylic acids

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Abstract
The dissociation equilibrium constants of some is‐α‐phenyl‐β‐arylacrylic acids (Ar = 2‐pyridyl, 3‐pyridyl, 4‐pyridyl, 1‐naphthyl, 2‐naphthyl, anthracen‐9‐yl) have been measured in 80% aqueous 2‐methoxyethanol at 25°. The pKa values of these acids, together with those of p‐substituted phenyl, 2‐furyl, 2‐thienyl and selenophen‐2‐yl derivatives, have been rationalized by an equation involving separate contributions of polar, conjugative and steric effects of heterocycles. The pKa values of some E‐α‐phenyl‐β‐alkylacrylic acids (alk = methyl; ethyl; n‐propyl; i‐propyl; n‐butyl; i‐butyl) are also reported.