Which of the following compounds will not undergoAldol condensation reaction?

A. Benzaldehyde

B. Acetone

C. Propanal

D. Formaldehyde

E. Acetophenone

Choose the correct answers from the options given below:

A and D only

The correct answer is option 1. A and D only.

The aldol condensation reaction occurs when two molecules of aldehydes or ketones (or a combination of both) undergo a reaction in the presence of a base (like NaOH). For a compound to undergo aldol condensation, it must possess at least one α-hydrogen (a hydrogen atom attached to the carbon next to the carbonyl group, known as the α-carbon).

In the presence of a base, the α-hydrogen is abstracted, forming an enolate ion, which then reacts with another carbonyl compound. This leads to the formation of a β-hydroxyaldehyde (if starting with aldehydes) or β-hydroxyketone (if starting with ketones), which can then dehydrate to form an α,β-unsaturated carbonyl compound.

Conditions for Aldol Condensation:

Presence of α-hydrogens: The compound must have at least one hydrogen on the α-carbon, which is adjacent to the carbonyl group.

Basic medium: A base abstracts the α-hydrogen to form an enolate ion, which is essential for the reaction to proceed.

Analysis of the Given Compounds:

A. Benzaldehyde

It does not have any α-hydrogens because the carbonyl group is directly attached to the benzene ring (no adjacent CH bonds). Since there are no α-hydrogens, benzaldehyde cannot form an enolate ion and cannot undergo aldol condensation.

Conclusion: Benzaldehyde cannot undergo aldol condensation.

B. Acetone

It has two α-hydrogens on each of the methyl groups (\( CH_3 \)) adjacent to the carbonyl group. These α-hydrogens can be abstracted by a base to form an enolate ion, which can then undergo aldol condensation.
Conclusion: Acetone can undergo aldol condensation.

C. Propanal :

Propanal has α-hydrogens on the CH₂ group next to the carbonyl group. These α-hydrogens can be abstracted to form an enolate ion, leading to aldol condensation.

Conclusion:Propanal can undergo aldol condensation.

D. Formaldehyde :

Formaldehyde has no α-hydrogens, as the carbonyl carbon is directly attached to a hydrogen atom. Without α-hydrogens, formaldehyde cannot form an enolate ion and cannot undergo aldol condensation.

Conclusion:Formaldehyde cannot undergo aldol condensation

E. Acetophenone :

Acetophenone has α-hydrogens on the methyl group (\( CH_3 \)) next to the carbonyl group. These hydrogens can be abstracted to form an enolate ion, allowing it to undergo aldol condensation.

Conclusion:Acetophenone can undergo aldol condensation.

The correct answer is 1. A and D only, as Benzaldehyde (A) and Formaldehyde (D) cannot undergo aldol condensation.