Which of the following will not give aldol condensation ?

Options

A. Phenyl acetaldehyde
B. 2 - Methylpentanal
C. Benzaldehyde
D. 1 - Phenylpropanone

Explanation

To determine which of the following compounds will not undergo aldol condensation, we need to identify whether each compound has at least one alpha hydrogen (α-H). Aldol condensation requires the presence of α-H on the carbon adjacent to the carbonyl group (aldehyde or ketone).

### Step-by-Step Solution:

1. **Understanding Aldol Condensation**:
- Aldol condensation is a reaction between aldehydes or ketones that have at least one α-H. The α-H is crucial because it allows the formation of an enolate ion, which is necessary for the condensation reaction.

2. **Analyzing the Compounds**:
- We will analyze each compound given in the question to check for the presence of α-H.

3. **Compound 1: Phenylacetaldehyde**:
- Structure: C6H5-CH2-CHO
- The α-carbon is the one adjacent to the carbonyl (CHO). In this case, the α-carbon is CH2, which has two α-H atoms.
- Conclusion: **Has α-H**; can undergo aldol condensation.

4. **Compound 2: 2-Methylpentanal**:
- Structure: CH3-CH2-CH(CH3)-CHO
- The α-carbon is the one adjacent to the carbonyl (CHO). The α-carbon here is CH, which has one α-H atom.
- Conclusion: **Has α-H**; can undergo aldol condensation.

5. **Compound 3: Benzaldehyde**:
- Structure: C6H5-CHO
- The α-carbon is the one adjacent to the carbonyl (CHO). In this case, the adjacent carbon (C6H5) has no hydrogen atoms because all four valencies of the carbon are satisfied by bonds to other carbons.
- Conclusion: **No α-H**; cannot undergo aldol condensation.

6. **Compound 4: 1-Phenylpropanol**:
- Structure: C6H5-CH2-CH2OH
- The α-carbon is the one adjacent to the carbonyl (in this case, the alcohol group). The α-carbon here is CH2, which has two α-H atoms.
- Conclusion: **Has α-H**; can undergo aldol condensation.

7. **Final Conclusion**:
- The only compound that does not have an α-H and therefore cannot undergo aldol condensation is **Benzaldehyde**.

### Answer:
The compound that will not give aldol condensation is **Benzaldehyde**.

---