应用量化参数研究羧酸的结构和pKa值的关系

Correlation analysis of structures and pKa values of carboxylic acids by quantum-chemical descriptors

应用密度泛函B3LYP/6-311++G^(?)法得30种羧酸分子的优势构象,再计算羧酸-水构成的氢键复合物,获得优势构象和复合物的结构参数,并将这些参数与羧酸pKa值相比。羧基C-O键长、羧基氢自然键轨道电荷以及复合物的氢键键长和结合能等参数,与羧酸pKa实验值具有良好的线性关系。以水为探针分子获得氢键复合物结构参数的方法,可预期在预测其它含有酸性基团化合物酸性的强弱方面推广应用。

The structures of 30 carboxylic acids and carboxylic acids-water complexes are optimized at B3LYP/6-311 ＋ ＋ G^＊＊ level to obtain structural parameters. Several parameters, such as the C-O bond length and the natural atomic charge on hydrogen atom of car- boxylic group, the hydrogen-bond length and binding energy of hydrogen-bonded complexes, are linearly correlated with known experimental pKa values of carboxylic acids. This study suggests that calculated parameters of hydrogen-bonded complexes with water as a single probe molecule may be extended to determine the acidity of other compounds with acidic functional group.