State of the hydroxide ion in water and aqueous solutions

Analysis of these experimental facts leads to the conclusion that in water and aqueous solutions of alkali metal hydroxides it is extremely probable that the hydroxide ion exists in the form H3O2−. The marked displacement of the extrapolated chemical shift of the proton of the H3O2− ion towards weak fields and the displacement of the frequency of the bending vibrations of the OH bond towards higher frequencies for hydroxide solutions indicate strong hydrogen bonding between the OH− ion and the H2O molecule. The comparatively low heat of hydration of the OH− ion (111 cal/mole) compared with the heat of hydration of the H+ ion (276 cal/mole) cannot, as has been shown, serve as proof that there is no strong electrostatic bond between the OH− ion and a water molecule. All the heat of hydration is used up in the formation of this bond; this can be regarded as additional confirmation of the hydrophobic nature of the ion produced. The experimental data on the absolute value of the chemical shift of the proton of the H3O2− ion indicate the important role played by the excited state of the proton in this complex. This conclusion agrees with the spectroscopic data.