which of the following is not an isomer of pentanal

Options

A. 2-pentanone
B. 3-pentanone
C. 3-Methylbutanone
D. 3-Methyl-2-butanol

Answer

To determine which of the following compounds is not an isomer of pentanal, we first need to understand what isomers are. Isomers are compounds that have the same molecular formula but different structural arrangements of atoms.

### Step-by-Step Solution:

1. **Identify the Molecular Formula of Pentanal:**
- Pentanal is an aldehyde with the molecular formula C5H10O. The "pent" prefix indicates that there are five carbon atoms in the longest chain, and the "al" suffix indicates the presence of an aldehyde functional group.

2. **List the Given Options:**
- We need to analyze the structures of the following compounds to see if they are isomers of pentanal:
- 2-pentanone
- 3-pentanone
- 3-methylbutanone
- 3-methylbutanol

3. **Analyze Each Option:**
- **2-pentanone:**
- Structure: This compound has a ketone functional group on the second carbon of a five-carbon chain.
- Molecular Formula: C5H10O (isomer of pentanal).

- **3-pentanone:**
- Structure: This compound has a ketone functional group on the third carbon of a five-carbon chain.
- Molecular Formula: C5H10O (isomer of pentanal).

- **3-methylbutanone:**
- Structure: This compound has a four-carbon chain (butanone) with a methyl group on the third carbon. The total number of carbon atoms is still five.
- Molecular Formula: C5H10O (isomer of pentanal).

- **3-methylbutanol:**
- Structure: This compound has a four-carbon chain (butanol) with a methyl group on the third carbon and an alcohol functional group (-OH).
- Molecular Formula: C5H12O (not an isomer of pentanal).

4. **Conclusion:**
- Among the given options, 3-methylbutanol has a different molecular formula (C5H12O) compared to pentanal (C5H10O). Therefore, it is not an isomer of pentanal.

### Final Answer:
**3-methylbutanol is not an isomer of pentanal.**