## Abstract

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 ΔH_{prot, HSO3F}(B) = - PA(B) + ΔE_{t}(BH^{+}) - ΔE_{t}(B) + β, where PA(B) is the gas phase proton affinity for base B, ΔE_{t}(BH^{+}) is the SCIPCM solvation energy for the conjugate acid, and ΔE_{t}(B) is the solvation energy for the base. A fit to experimental values of ΔH_{prot, HSO3F}(B) for 10 neutral bases (H_{2}O, MeOH, Me_{2}O, H_{2}S, MeSH, Me_{2}S, NH_{3}, MeNH_{2}, Me_{2}NH, and PH_{3}) gives β = 238.4 ± 2.9 kcal/mol when ΔΔE_{t} 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 ΔH_{prot, 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 language | English |
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Pages (from-to) | 250-257 |

Number of pages | 8 |

Journal | Journal of Computational Chemistry |

Volume | 19 |

Issue number | 2 |

DOIs | |

Publication status | Published - 30 Jan 1998 |

Externally published | Yes |

## Keywords

- Acidities
- Fluorosulfonic acid
- Protonation energies
- Solvation

## ASJC Scopus subject areas

- General Chemistry
- Computational Mathematics