If carboxylic acids have electron withdrawing groups, they are stronger than unsubstituted acids Cl H CH-C-CO2H>CH-C-cC0 H)>C1--C--C0OH> C-CO,H H pKa 0.7 148 285 4.75 由于氯原子电负性比碳大,氯原子表现出拉电子 诱导效应( inductive effect),使羧酸容易电离出质子(H)。 羧酸的酸性增强。If carboxylic acids have electron￾withdrawing groups, they are stronger than unsubstituted acids. Cl Cl C Cl CO2H Cl Cl C H CO2H H Cl C H CO2H H H C H CO2H pKa 0.7 1.48 2.85 4.75 由于氯原子电负性比碳大，氯原子表现出拉电子 诱导效应(Inductive effect)，使羧酸容易电离出质子(H+ )。 羧酸的酸性增强