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不少的教科书特别是有机化学教科书在分析羧酸酸性与其结构关系时是这样说的:一个羧酸的酸性强度,主要决定于羧酸和它的离解负离子间的稳定性的差别,如果负离子比它的酸稳定,则离解平衡向生成负离子和H~+的方向进行,PKa值小,酸性强;反之,则PKa值大,酸性弱,任何能使负离子更加稳定的结构因素,都会使酸性增强;任何使负离子不稳定的结构因素将会使酸性减弱;吸电子取代基由于-Ⅰ诱导效应分散了羧酸根的负电荷,能量降低,使负离子稳定,所以增强酸性;推电子取代基,由于+Ⅰ诱导效应,增加了羧酸根上的负电荷,使负离子能量升高不稳定,因此酸性减弱。
Many textbooks, especially organic chemistry textbooks, say this when analyzing the acidity of a carboxylic acid and its structure: The acid strength of a carboxylic acid depends primarily on the difference in stability between the carboxylic acid and its dissociating anions. If the anion ratio Its acid stability, the dissociation equilibrium to the generation of negative ions and H ~ + direction, PKa value is small, strong acid; Conversely, the PKa value, weak acid, any anion can make more stable structural factors, will make the acid enhanced ; Any structural element that destabilizes the anion will weaken the acidity; the electron-withdrawing substituent disperses the negative charge of the carboxylate due to the -I inducing effect, reduces the energy and stabilizes the negative ion, thereby enhancing the acidity; Ⅰ induction effect, increasing the negative charge on the carboxylate, the anion energy instability, so weakened acidity.