Which of the following does not undergo Cannizzaro reaction?

Options

A. Benzaldehyde
B. 2 - Methylpropanal
C. p - Methoxybenzaldehyde
D. 2, 2 - Dimethylpropanal

Explanation

To determine which of the given compounds does not undergo the Cannizzaro reaction, we need to analyze each option based on the presence of alpha-hydrogens. The Cannizzaro reaction occurs with aldehydes that do not have alpha-hydrogens.

### Step-by-Step Solution:

1. **Understanding the Cannizzaro Reaction**:
- The Cannizzaro reaction is a redox reaction where aldehydes without alpha-hydrogens are disproportionated in the presence of a strong base, leading to the formation of an alcohol and a carboxylic acid.

2. **Identifying Alpha-Hydrogens**:
- Alpha-hydrogens are the hydrogen atoms attached to the carbon atom adjacent to the carbonyl group (C=O). If a compound has no alpha-hydrogens, it can undergo the Cannizzaro reaction.

3. **Analyzing Each Option**:
- **Option A: Benzaldehyde (C6H5CHO)**:
- Structure: C6H5-CHO
- Benzaldehyde has no alpha-hydrogens (the carbon adjacent to the carbonyl is part of the aromatic ring). Thus, it can undergo the Cannizzaro reaction.

- **Option B: 2-Methylpropanol (C5H12O)**:
- Structure: (CH3)2CH-CH2OH
- This compound has alpha-hydrogens (the carbon adjacent to the hydroxyl group has hydrogens). Therefore, it does not undergo the Cannizzaro reaction.

- **Option C: Para-Methoxybenzaldehyde (C8H9O2)**:
- Structure: C6H4(OCH3)CHO
- This compound also has no alpha-hydrogens (the carbon adjacent to the carbonyl is part of the aromatic ring). Thus, it can undergo the Cannizzaro reaction.

- **Option D: 2,2-Dimethylpropanol (C5H12O)**:
- Structure: (CH3)3C-CH2OH
- This compound has no alpha-hydrogens (the carbon adjacent to the carbonyl has no hydrogens). Thus, it can undergo the Cannizzaro reaction.

4. **Conclusion**:
- The only compound that does not undergo the Cannizzaro reaction is **2-Methylpropanol** (Option B), as it contains alpha-hydrogens.

### Final Answer:
**2-Methylpropanol (Option B) does not undergo the Cannizzaro reaction.**