Which of the following will not undergo aldol condensation-

Options

A. Acetaldehyde
B. Propanaldehyde
C. Benzaldehyde
D. Trideuteroacetaldehyde

Answer

To determine which compound will not undergo aldol condensation, we need to understand the requirements for this reaction. Aldol condensation requires the presence of alpha-hydrogens (α-H) on the carbon adjacent to the carbonyl group. Here’s a step-by-step solution:

### Step 1: Understand Aldol Condensation
Aldol condensation is a reaction between two carbonyl compounds (aldehydes or ketones) in the presence of a base. The base abstracts an alpha-hydrogen from one of the carbonyl compounds, forming an enolate ion, which then acts as a nucleophile and attacks another carbonyl compound.

**Hint:** Remember that the presence of alpha-hydrogens is crucial for the formation of enolate ions.

### Step 2: Identify Alpha-Hydrogens
Alpha-hydrogens are the hydrogens attached to the carbon atom that is adjacent to the carbonyl group. If a compound lacks alpha-hydrogens, it cannot undergo aldol condensation.

**Hint:** Look for the carbon directly next to the carbonyl group to identify alpha-hydrogens.

### Step 3: Analyze the Given Compounds
Let’s consider the compounds mentioned in the question:

1. **Acetaldehyde (CH3CHO)**:
- Structure: CH3-CH=O
- Alpha-hydrogens: 3 (from the CH3 group)
- Conclusion: Can undergo aldol condensation.

2. **Propanal (CH3CH2CHO)**:
- Structure: CH3-CH2-CH=O
- Alpha-hydrogens: 2 (from the CH2 group)
- Conclusion: Can undergo aldol condensation.

3. **Benzaldehyde (C6H5CHO)**:
- Structure: C6H5-CHO
- Alpha-hydrogens: 0 (the carbon adjacent to the carbonyl is part of the benzene ring and has no hydrogen)
- Conclusion: Cannot undergo aldol condensation.

4. **Trideuterated Acetaldehyde (CD2HCHO)**:
- Structure: CD2H-CHO
- Alpha-hydrogens: 2 (the CH2 group has deuterium instead of hydrogen, but it still counts as an alpha-hydrogen)
- Conclusion: Can undergo aldol condensation.

### Step 4: Conclusion
From the analysis, the compound that will not undergo aldol condensation is **Benzaldehyde** because it lacks alpha-hydrogens.

**Final Answer:** Benzaldehyde will not undergo aldol condensation.

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