Protonation enthalpies in fluorosulfonic acid using ab initio self-consistent reaction field theory

Nathan J. Harris, Tomohiko Ohwada, Koop Lammertsma

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12 Citations (Scopus)


Electrostatic solvation free energies were computed for several small neutral bases and their conjugate acids using a continuum solvation model called the self-consistent isodensity polarizable continuum model (SCIPCM). The solvation energies were computed at the restricted Hartree-Fock (RHF) and second-order Møller-Plesset (MP2) levels of theory, as well as with the Becke3-Lee-Yang-Parr (B3LYP) density functional theory, using the standard 6-31G** Gaussian basis set. The RHF solvation energies are similar to those computed at the correlated MP2 and B3LYP theoretical levels. A model for computing protonation enthalpies for neutral bases in fluorosulfonic acid solvent leads to the equation ΔHprot, HSO3F(B) = - PA(B) + ΔEt(BH+) - ΔEt(B) + β, where PA(B) is the gas phase proton affinity for base B, ΔEt(BH+) is the SCIPCM solvation energy for the conjugate acid, and ΔEt(B) is the solvation energy for the base. A fit to experimental values of ΔHprot, HSO3F(B) for 10 neutral bases (H2O, MeOH, Me2O, H2S, MeSH, Me2S, NH3, MeNH2, Me2NH, and PH3) gives β = 238.4 ± 2.9 kcal/mol when ΔΔEt is computed using the 0.0004 e · bohr-3 isodensity surface for defining the solute cavity at the RHF/6-31G** level. The model predicts that for carbon monoxide ΔHprot, HSO3F(CO) = 10 kcal/mol. Thus, protonation of CO is endothermic, and the conjugate acid HCO+ (formyl cation) behaves as a strong acid in fluorosulfonic acid.

Original languageEnglish
Pages (from-to)250-257
Number of pages8
JournalJournal of Computational Chemistry
Issue number2
Publication statusPublished - 30 Jan 1998
Externally publishedYes


  • Acidities
  • Fluorosulfonic acid
  • Protonation energies
  • Solvation

ASJC Scopus subject areas

  • General Chemistry
  • Computational Mathematics


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