气相酸性理论(Ⅱ)——与氢相连的氢强度的影响

Theory of Gas-Phase Acidity (Ⅱ)——the Effect of the Strength of the Bond Linking the Hydrogen

前文己报道氢电荷QH是影响酸性的重要因素,但仅限于CH、NH和OH酸,把与氢相连的原子B种类扩大到H、F、Si、P、S、Cl并用CNDO/2法作全几何优化进行研究时,发现脱质子能EDP与QH的相关性变劣,见表1.估计其原因与HB键强度有关,故须考虑HB键强度来研究EDP的规律。 键强度有热力学、量子化学等多种衡量方法,从热力学的角度,键能是键强度的普遍衡量,然而键能有不同的概念,一种是键解离能。

CNDO/2 study of neutral and cationic HH, CH, NH, FH, SiH, PH, SH, and CIH acids shows that acidity relates to the strength of the bontl linking the acidic hydrogen as well as the charge of the hydrogen. Using diatomic contribution to energy as a measure of bond strength, we performed linearly regressions of depr’otonation energy with respect to hydrogen charge and the diatomic contribution to energy. The correlation is good in the case of cationic acids and worse in the, case of neutral acids.