CHEMISTRY · Single correct · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
Dichloroacetic acid has a pKa of 1.48, whereas monochloroacetic acid has a pKa of 2.85. Which of the following best explains why the dichloro compound is the stronger acid?
(a) The two chlorine atoms are highly electronegative and pull electron density from the O–H bond itself, weakening it and allowing the proton to detach more readily.
(b) The two chlorine atoms withdraw electron density inductively, stabilizing the conjugate base more than a single chlorine atom.
(c) The lone pairs on the chlorine atoms can overlap with the carboxylate π system, providing additional resonance structures that disperse the negative charge.
(d) With two chlorines present, the molecule forms stronger hydrogen bonds with water, so dissociation of the proton is more favored.