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

✍ Scribed by Harris, Nathan J.; Ohwada, Tomohiko; Lammertsma, Koop

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 175 KB
• Volume: 19
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(19980130)19:2<250::aid-jcc18>3.0.co;2-l

✦ Synopsis

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 Ž . SCIPCM . The solvation energies were computed at the restricted Hartree᎐Fock Ž . Ž . RHF and second-order Møller᎐Plesset MP2 levels of theory, as well as with Ž . the Becke3᎐Lee᎐Yang᎐Parr B3LYP density functional theory, using the standard 6᎐31G UU 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

prot, HSO F t t 3 Ž . Ž q . where PA B is the gas phase proton affinity for base B, ⌬ E BH is the t Ž . SCIPCM solvation energy for the conjugate acid, and ⌬ E B is the solvation t Ž . energy for the base. A fit to experimental values of ⌬ H B for 10 neutral prot, HSO F 3 Ž bases H O, MeOH, Me O, H S, MeSH, Me S, NH , MeNH , Me NH, and 2 2 2 2 3 2 2

. PH gives ␤ s 238.4 " 2.9 kcalrmol when ⌬⌬ E is computed using the 0.0004 3 t e и bohr y3 isodensity surface for defining the solute cavity at the RHFr6᎐31G UU Ž . level. The model predicts that for carbon monoxide ⌬ H CO s 10 prot, HSO F 3 kcalrmol. Thus, protonation of CO is endothermic, and the conjugate acid q Ž . HCO formyl cation behaves as a strong acid in fluorosulfonic acid.