用相对Gibbs自由能方法计算羧酸的pK_a值

Calculation on pK_a Values of Carboxylic Acids in Aqueous Solution Using Relative Gibbs Free Energy

运用密度泛函方法以及连续极化溶剂模型(PCM),在B3LYP/6-31+G(d,p)水平上计算了86种羧酸在水溶液中的97个pKa值.在本文pKa值的计算中,用羧酸在水溶液中的电离反应直接计算羧酸电离Gibbs自由能,并用相对Gibbs自由能来计算羧酸的pKa值.结果表明,计算值能很好地与实验值吻合,其标准偏差为±0.36pKa单位.

The 97 pKa values of 86 carboxylic acids in aqueous solution were calculated with density functional theory method at the level of B3 LYP/6 -31 ＋ G（ d, p） and the polarizable continuum model （PCM） was used to describe the solvent. The pK. values were directly calculated employing the relative Gibbs free energies of the carboxylic acid dissociations in aqueous solution. In this way we obtained an approach in which pKa values of ic acids in aqueous solution can be predicted with the standard deviation of 0.36 in pKa unit.