title: Aqueous acidities of primary benzenesulfonamides: Quantum chemical predictions based on density functional theory and SMD.
abstract: Aqueous pK(a) of selected primary benzenesulfonamides are predicted in a systematic manner using density functional theory methods and the SMD solvent model together with direct and proton exchange thermodynamic cycles. Some test calculations were also performed using high-level composite CBS-QB3 approach. The direct scheme generally does not yield a satisfactory agreement between calculated and measured acidities due to a severe overestimation of the Gibbs free energy changes of the gas-phase deprotonation reaction by the used exchange-correlation functionals. The relative pK(a) values calculated using proton exchange method compare to experimental data very well in both qualitative and quantitative terms, with a mean absolute error of about 0.4 pK(a) units. To achieve this accuracy, we find it mandatory to perform geometry optimization of the neutral and anionic species in the gas and solution phases separately, because different conformations are stabilized in these two cases. We have attempted to evaluate the effect of the conformer-averaged free energies in the pK(a) predictions, and the general conclusion is that this procedure is highly too costly as compared with the very small improvement we have gained.
authors.affiliation: VšĮ "Aukštieji algoritmai", A. Mickevičiaus g. 29, LT-08117, Vilnius, Lithuania.|Department of General Physics and Spectroscopy, Faculty of Physics, Vilnius University, Saulėtekio al. 9, LT-10222, Vilnius, Lithuania.
authors.forename: Kęstutis
authors.initials: K
authors.lastname: Aidas
authors.affiliation: VšĮ "Aukštieji algoritmai", A. Mickevičiaus g. 29, LT-08117, Vilnius, Lithuania.
authors.forename: Kiril
authors.initials: K
authors.lastname: Lanevskij
authors.affiliation: VšĮ "Aukštieji algoritmai", A. Mickevičiaus g. 29, LT-08117, Vilnius, Lithuania.
authors.forename: Rytis
authors.initials: R
authors.lastname: Kubilius
authors.affiliation: VšĮ "Aukštieji algoritmai", A. Mickevičiaus g. 29, LT-08117, Vilnius, Lithuania.
authors.forename: Liutauras
authors.initials: L
authors.lastname: Juška
authors.affiliation: Department of General Physics and Spectroscopy, Faculty of Physics, Vilnius University, Saulėtekio al. 9, LT-10222, Vilnius, Lithuania.
authors.forename: Daumantas
authors.initials: D
authors.lastname: Petkevičius
authors.affiliation: VšĮ "Aukštieji algoritmai", A. Mickevičiaus g. 29, LT-08117, Vilnius, Lithuania.|ACD/Labs, Inc., 8 King Street East, Suite 107, Toronto, Ontario, Canada, M5C 1B5.
authors.forename: Pranas
authors.initials: P
authors.lastname: Japertas
mesh_terms: D000143:Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D011789:Quantum Theory; D013449:Sulfonamides / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D000096926:Benzenesulfonamides
chemical_list: D000143:Acids; D013449:Sulfonamides; D014867:Water; D000096926:Benzenesulfonamides
keywords: SMD; aqueous acidity; density functional theory; primary benzenesulfonamides; thermodynamic cycle