pKa values of estrone, 17β-estradiol and 2-methoxyestrone

Abstract The acid ionization constants of estrone (10.77), 17β-estradiol (10.71) and 2-methoxyestrone (10.81) have been determined spectrophoto-metrically and shown to be consistent with the additivity of substituent effects on the phenol ring. Previously published values for estrone (10.914) and 17β-estradiol (10.078) are shown to be incorrect, at variance with the established trend for phenols, and inconsistent with the similarity of the compounds.