Linear free energy relationships were established between reaction rate constants of alcohols and amines with ethyi magnesium bromide in diethyl ether at 25 °, and their pK values in terms of Bronsted equation, which are: for alcohols, log k = — 0,09 pK + 0,93 (at 25 °C) and for amines, log k = — 0,07 pK -J- 0,78 (at 25 °C) From these equations, the relative pK values of amines and alcohols can be predic-’ ted by measuring their reaction rate constants with ethyi magnesium bromide in diethyl ether, at 25°C.