Which of the following reactions involve carbanion enolalte as reactive intermediate?

Options

A. Kolbe-Schmidt reaction
B. Reimer-Tiemann reaction
C. Claisen condensation
D. Aldol condensation

Answer

To determine which reactions involve carbanion enolate as a reactive intermediate, we can analyze the process of aldol condensation, which is a key reaction in organic chemistry involving aldehydes and ketones.

### Step-by-Step Solution:

1. **Understanding Carbanion Enolate Formation**:
- In the aldol condensation reaction, a base abstracts an alpha hydrogen from an aldehyde or ketone. This results in the formation of an enolate ion, which is a carbanion stabilized by resonance.
- The general structure of an enolate ion can be represented as R2C=CHO^-, where R represents the alkyl or aryl groups attached to the carbon.

2. **Aldol Condensation Mechanism**:
- The first step involves the deprotonation of the alpha carbon (the carbon adjacent to the carbonyl group) by a strong base (like NaOH or KOH), leading to the formation of the enolate ion.
- This enolate ion can then attack the carbonyl carbon of another aldehyde or ketone molecule, leading to the formation of a β-hydroxy aldehyde or ketone.

3. **Product Formation**:
- The β-hydroxy aldehyde or ketone can undergo dehydration (loss of water) to form an α,β-unsaturated carbonyl compound.
- The overall reaction can be summarized as follows:
- Aldehyde (or ketone) + Base → Enolate Ion → Nucleophilic Attack → β-Hydroxy Carbonyl → Dehydration → α,β-Unsaturated Carbonyl.

4. **Conclusion**:
- Based on the above analysis, the aldol condensation reaction is the one that involves a carbanion enolate as a reactive intermediate.
- Therefore, the correct answer to the question is that aldol condensation is the reaction that involves a carbanion enolate as a reactive intermediate.

### Final Answer:
- The reaction that involves carbanion enolate as a reactive intermediate is **Aldol Condensation**.