hydroxyl group

pKa

Catechin

Epicatechin

O₃₀–H₃₁

21.77

21.70

O₃₂–H₃₃

9.92

10.56

O₃₄–H₃₅

10.47

11.21

O₂₆–H₂₇

11.78

11.71

O₂₈–H₂₉

7.53

6.77