Accurate pKa Calculations for Carboxylic Acids Using Complete Basis Set and Gaussian-n Models Combined with CPCM Continuum Solvation Methods
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- 作者：Matthew D. Liptak and George C. Shields
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：August 1, 2001
- 年：2001
- 卷：123
- 期：30
- 页码：7314 - 7319
- 全文大小：64K
- 年卷期：v.123,no.30(August 1, 2001)
- ISSN：1520-5126
文摘
Complete Basis Set and Gaussian-n methods were combined with CPCM continuum solvationmethods to calculate pKa values for six carboxylic acids. An experimental value of -264.61 kcal/mol for thefree energy of solvation of H+, 
Gs(H+), was combined with a value for Ggas(H+) of -6.28 kcal/mol tocalculate pKa values with Cycle 1. The Complete Basis Set gas-phase methods used to calculate gas-phasefree energies are very accurate, with mean unsigned errors of 0.3 kcal/mol and standard deviations of 0.4kcal/mol. The CPCM solvation calculations used to calculate condensed-phase free energies are slightly lessaccurate than the gas-phase models, and the best method has a mean unsigned error and standard deviation of0.4 and 0.5 kcal/mol, respectively. The use of Cycle 1 and the Complete Basis Set models combined with theCPCM solvation methods yielded pKa values accurate to less than half a pKa unit.
Gs(H+), was combined with a value for Ggas(H+) of -6.28 kcal/mol tocalculate pKa values with Cycle 1. The Complete Basis Set gas-phase methods used to calculate gas-phasefree energies are very accurate, with mean unsigned errors of 0.3 kcal/mol and standard deviations of 0.4kcal/mol. The CPCM solvation calculations used to calculate condensed-phase free energies are slightly lessaccurate than the gas-phase models, and the best method has a mean unsigned error and standard deviation of0.4 and 0.5 kcal/mol, respectively. The use of Cycle 1 and the Complete Basis Set models combined with theCPCM solvation methods yielded pKa values accurate to less than half a pKa unit.