Acid and base solutions as well as polyelectrolytes are studied by FTIR spectroscopy. For the understanding of all these systems it is important that homoconjugated B+H^…B↔B^…H⁺B as well as heteroconjugated AH^…B↔A^-…H⁺B bonds show large proton polarizabilities. They are indicated by intense continua in the infrared spectra.

The molecular processes and the thermodynamics of the dissociation process are discussed in the case of  strong acids. The following solvate structures of the excess proton play an important role. H₅O₂⁺ with an easily polarizable hydrogen bond. The center of H₉O₄ fluctuates between the O atoms of H₅O₂⁺ with the tunneling frequency of the proton in H₅O₂⁺. The field sensitive mechanism of the high conductivity of acid solutions is explained on the molecular level.

With weak acids the AH^…OH₂ hydrogen bonds show already large proton polarizability before the acid proton transfers to the water molecule. The reason is the large negative entropy term ΔS⁰_I of the proton shift in this hydrogen bond arising by the large order around the polar structure A^-…H⁺B.

It is discussed that and why with phosphorous containing acids and with arsenic acid also the acid -acid hydrogen bonds show large proton polarizability.

With strong bases the H₃O₂^- group containing a hydrogen bond with large proton polarizability is of main significance. Not only in aqueous solutions but also in other solution, for instance, in alcohols hydrogen bonds with large proton polarizability are of great importance.

All these results are of significance for the understanding of the behavior of acid and base solutions.