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MCAT Question A Day - 4/17/13 - Answer!

The carboxyl group gives rise to which properties?

A.  Acidic, undergoes electrophilic addition, hydrophilic
B.  Basic, undergoes nucleophilic substitution, hydrophobic
C.  Acidic, undergoes nucleophilic substitution, hydrophilic
D.  Acidic, undergoes nucleophilic addition, hydrophilic

The correct answer is (C). The carboxylate anion is resonance stabilized, giving the carboxyl group its acidic properties.

Carboxylic acids and their derivatives typically undergo nucleophilic substitution in which —Cl, —OH, —NH2, —OOCR, or OR is replaced by some other basic group.  For an aldehyde or ketone to undergo nucleophilic substitution, a hydride (H2) or alkide (R2), the strongest bases of all, would have to leave. Thus, they undergo addition as opposed to substitution.