Skip to main content


Applying the unified pH scale: absolute acidities in the gas phase and anchor points for eleven representative liquid media

Article metrics

  • 5828 Accesses

The investigations on our recently introduced unified acidity scale [1] based on the absolute chemical potential of the proton pointed out the inadequateness of the established GA scale. Earlier it was inter alia found that, when trying to correlate pKa with GA values, in several cases the correlation was broken without any sufficient explanation [2, 3]. However, the GA does not take into account the pressure dependent speciation in the gas phase. In this contribution we systematically extend the theory of acidity in the gas phase from standard GAs and GBs to the real existing bulk phases [4].

Furthermore we present the rCCC (relaxed COSMO cluster-continuum) model [5], a quantum chemical solvation model for the calculation of Gibbs solvation energies of the proton with good accuracy. The rCCC values can be used to anchor individual pH scales in different solvents to our universal scale.


  1. 1.

    Himmel D, Goll SK, Leito I, Krossing I: A unified pH scale for all phases. Angew Chem Int Ed Engl. 2010, 49: 6885-6888. 10.1002/anie.201000252.

  2. 2.

    Koppel IA, Koppel J, Pihl V, Leito I, Mishima M, Vlasov VM, Yagupolskii LM, Taft RW: Comparison of Brønsted acidities of neutral CH acids in gas phase and dimethyl sulfoxide. J Chem Soc, Perkin Trans 2. 2000, 1125-1133.

  3. 3.

    Kütt A, Leito I, Kaljurand I, Sooväli L, Vlasov VM, Yagupolskii LM, Koppel IA: A comprehensive self-consistent spectrophotometric acidity scale of neutral Brønsted acids in acetonitrile. J Org Chem. 2006, 71: 2829-2838. 10.1021/jo060031y.

  4. 4.

    Himmel D, Goll SK, Leito I, Krossing I: . to be published

  5. 5.

    Himmel D, Goll SK, Leito I, Krossing I: Anchor points for the unified Brønsted acidity scale: The rCCC model for the calculation of standard Gibbs energies of proton solvation in eleven representative liquid media. Chem Eur J. 2011, 17: 5808-5826. 10.1002/chem.201003164.

Download references

Author information

Correspondence to Sascha K Goll.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Reprints and Permissions

About this article


  • Acidity
  • Quantum Chemical
  • Solvation Energy
  • Solvation Model
  • Bulk Phasis