Question

Carbonyl compounds can be protonated on the carbonyl oxygen. Protonation of the carbonyl oxygen gives a species whose positive charge is delocalized by resonance. Explain why acetic acid (ethanoic acid) is more readily protonated than acetone (propanone).

Answer 1

Answer:

Full explanation is given below.

Explanation:

Positive charge on carbonyl oxygen atom in protonated acetic acid is delocalized by stronger electron donating resonating effect of lone pair of oxygen atom in adjacent -OH group.

Positive charge on carbonyl oxygen atom in protonated acetone is delocalized by weaker electron donating inductive effect of two adjacent methyl groups.

Higher the delocalization of positive charge, higher will be stability of protonated species. Hence acetic acid is more rapidly protonated.

Resonance structures of protonated acetic acid has been shown below.