Which of the following is not an isomer of butanal?

Options

A. (a) `2`-Butanone
B. (b) `2`-Methyl propanal
C. (c) `2`- Butanol
D. (d) But-2-en-1-ol

Explanation

To determine which of the following compounds is not an isomer of butanal, we need to analyze the structures and chemical formulas of the given options. Butanal is an aldehyde with the chemical formula C4H8O.

### Step-by-Step Solution:

1. **Identify the Structure of Butanal**:
- Butanal has a four-carbon chain with an aldehyde group (-CHO) at one end.
- The chemical formula for butanal is C4H8O.

2. **List the Options**:
- We need to analyze the given options to see which one does not match the formula of butanal.

3. **Analyze Each Option**:
- **Option 1: 2-Methylpropanal**:
- Structure: A three-carbon chain (propane) with a methyl group on the second carbon and an aldehyde group.
- Formula: C4H8O (matches butanal).
- **Option 2: 2-Butanone**:
- Structure: A four-carbon chain with a ketone group (C=O) at the second carbon.
- Formula: C4H8O (matches butanal).
- **Option 3: 2-Butanol**:
- Structure: A four-carbon chain with an alcohol group (-OH) on the second carbon.
- Formula: C4H10O (does not match butanal).
- **Option 4: But-2-ene-1-ol**:
- Structure: A four-carbon chain with a double bond between the second and third carbons and an alcohol group at the first carbon.
- Formula: C4H8O (matches butanal).

4. **Conclusion**:
- The compound that does not have the same chemical formula as butanal is **2-Butanol (Option 3)**, which has the formula C4H10O.

### Final Answer:
**2-Butanol is not an isomer of butanal.**