Chapter 20: Q14P b. (page 1062)

Question: A carboxylic acid has two oxygen atoms, each with two nonbonding pairs of electrons.
Draw the resonance forms of a carboxylic acid that is protonated on the hydroxy oxygen atom.
Compare the resonance forms with those given previously for an acid protonated on the carbonyl oxygen atom.
Explain why the carbonyl oxygen atom of a carboxylic acid is more basic than the hydroxy oxygen.

Short Answer

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Answer

(b) The resonance forms of carboxylic acid, which is protonated on the hydroxyl oxygen atom, are:

The resonance forms of carboxylic acid, which is protonated on the carbonyl oxygen atom, are:

Step by step solution

Protonation

Protonation is adding proton (hydrogen cation) to a compound like ammonia, carboxylic acid etc., and forms a conjugate acid.The opposite of protonation is deprotonation, which means the removal of a proton.

Comparison of resonance forms of protonation of hydroxyl oxygen and protonation of carbonyl oxygen

(b) Two resonance forms are formed when protonation happens on the hydroxyl oxygen atom. One of which is BAD because of adjacent positive charges. In the case of protonation on the carbonyl oxygen atom, there are three resonance forms, and all three distribute the positive charge over three atoms without any charge separation. The protonation in the case of the carbonyl oxygen atom is good. The protonation of both the hydroxy oxygen and carbonyl oxygen atom is shown as: