Question

Aldol condensation does not occur between

• A. Two different aldehydes
• B. Two different ketones
• C. An aldehyde and a ketone
• D. An aldehyde and an ester

Answer 1

The correct option is D

An aldehyde and an ester

The explanation for the correct option:

Option (D): An aldehyde and an ester

1. In organic chemistry, an aldol condensation occurs when an enol or enolate ion containing $\mathrm{\alpha }-$H interacts with a carbonyl compound containing $\mathrm{\alpha }-$H to generate $\mathrm{\beta }-$hydroxy aldehyde or $\mathrm{\beta }-$hydroxy ketone, which is then dehydrated to provide a conjugated enone.
2. The nucleophilic addition of a ketone enolate to an aldehyde to generate $\mathrm{\beta }-$hydroxy ketone, or "aldol" (aldehyde + alcohol), is a structural unit found in many naturally occurring compounds and medications.
3. Crossed Aldol Condensation is a significant variant of an aldol condensation. In the Cross Aldol Reaction, two distinct compounds that both contain alpha hydrogen undergo a condensation reaction, resulting in the formation of up to four different types of products.
4. The ester will not include any carbonyl compounds and will not go through aldol condensation.
5. Hence, it is the correct option.

The explanation for the incorrect options:

Option (A): Two different aldehydes

1. In an aldol condensation, an enolate ion or enol attacks the carbonyl group of another aldehyde or ketone to produce a beta-hydroxy ketone or beta-hydroxy aldehyde.
2. This condensation is possible between two aldehydes.
3. Hence, it is an incorrect option

Option (B): Two different ketones

1. In an aldol condensation, an enolate ion or enol attacks the carbonyl group of another aldehyde or ketone to produce a beta-hydroxy ketone or beta-hydroxy aldehyde.
2. This condensation is possible between two ketones.
3. Hence, it is an incorrect option.

Option (C): An aldehyde and a ketone

1. In an aldol condensation, an enolate ion or enol attacks the carbonyl group of another aldehyde or ketone to produce a beta-hydroxy ketone or beta-hydroxy aldehyde.
2. This condensation is possible between an aldehyde and a ketone.
3. Hence, it is an incorrect option.

Therefore, aldol condensation does not occur between an aldehyde and an ester, option (D) is the correct option.