which functional group the most acidic and why? aldehyde, ketone, carboxylic acid, or ester.
The correct answer and explanation is:
The most acidic functional group among aldehydes, ketones, carboxylic acids, and esters is carboxylic acid.
Explanation:
Carboxylic acids contain the -COOH group, which consists of a carbonyl group (C=O) attached to a hydroxyl group (OH). The key factor that makes carboxylic acids the most acidic is the ability of the carboxyl group to lose a proton (H+) from the hydroxyl group. When the proton is removed, the resulting negatively charged carboxylate ion (RCOO-) is stabilized by resonance. The negative charge on the oxygen can be delocalized between the two oxygens of the carboxylate ion, spreading the negative charge and thus stabilizing the conjugate base.
This resonance stabilization of the conjugate base is what makes carboxylic acids more acidic compared to aldehydes, ketones, and esters, which lack this stabilizing feature.
- Aldehydes and ketones both contain a carbonyl group (C=O), but they do not have a hydroxyl group to release a proton, making them less acidic. In fact, the carbonyl group in aldehydes and ketones can act as an electrophile but does not ionize in the same way carboxylic acids do.
- Esters also contain a carbonyl group, but the oxygen attached to the carbonyl group is part of an ester linkage (RCOOR’), rather than a hydroxyl group. The ester functional group does not have the same ability to release a proton, and the conjugate base is not stabilized by resonance as in carboxylic acids.
Therefore, the ability of carboxylic acids to form a stable conjugate base through resonance after losing a proton makes them the most acidic of these functional groups.