Accurate relative pKa calculations for carboxylic acids using complete basis set and Gaussian-n models combined with continuum solvation methods

ACS Citation

Toth, A. M.; Liptak, M. D.; Phillips, D. L.; Shields, G. C. Accurate Relative pKa Calculations for Carboxylic Acids Using Complete Basis Set and Gaussian-N Models Combined with Continuum Solvation Methods. J. Chem. Phys. 2001, 114 (10), 4595-€“4606.

Abstract

The complete basis set methods CBS-4, CBS-QB3, and CBS-APNO, and the Gaussian methods G2 and G3 were used to calculate the gas phase energy differences between six different carboxylic acids and their respective anions. Two different continuum methods, SM5.42R and CPCM, were used to calculate the free energy differences of solvation for the acids and their anions. Relative pK(a) values were calculated for each acid using one of the acids as a reference point. The CBS-QB3 and CBS-APNO gas phase calculations, combined with the CPCM/HF/6-31+G(d)//HF/6-31G(d) or CPCM/HF/6-31+G(d)//HF/6-31+G(d) continuum solvation calculations on the lowest energy gas phase conformer, and with the conformationally averaged values, give results accurate to 1/2 pK(a) unit.

Source Name

Journal of Chemical Physics

Publication Date

2001

Volume

114

Issue

10

Page(s)

4595-4606

Document Type

Citation

Citation Type

Article

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