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 is not an isomer of pentanal, we first need to understand the structure and characteristics of pentanal and its possible isomers.

### Step-by-Step Solution:

1. **Identify the Structure of Pentanal:**
- Pentanal is an aldehyde with the molecular formula C5H10O. It has a straight-chain structure with five carbon atoms and the aldehyde functional group (-CHO) at one end.
- The structure can be represented as:
```
CH3-CH2-CH2-CH2-CHO
```

2. **Determine Possible Isomers:**
- Isomers are compounds with the same molecular formula but different structural arrangements. For pentanal, we can have:
- **Pentanal (Aldehyde)**: CH3-CH2-CH2-CH2-CHO
- **2-Pentanone (Ketone)**: CH3-CH2-CO-CH2-CH3 (Ketone at the second carbon)
- **3-Pentanone (Ketone)**: CH3-CO-CH2-CH2-CH3 (Ketone at the third carbon)
- **3-Methylbutanal**: CH3-CH2-CH(CH3)-CHO (Aldehyde with a methyl group on the third carbon)
- **3-Methyl-2-butanol**: CH3-CH(CH3)-CH2-CHOH (Alcohol with a hydroxyl group)

3. **Analyze Each Option:**
- **Pentanal**: Is an isomer (itself).
- **2-Pentanone**: Is an isomer (different functional group, but same molecular formula).
- **3-Pentanone**: Is an isomer (different functional group, but same molecular formula).
- **3-Methylbutanal**: Is an isomer (same molecular formula, different structure).
- **3-Methyl-2-butanol**: This compound has a hydroxyl group (-OH), which changes the functional group from aldehyde to alcohol, thus changing the molecular formula to C5H12O.

4. **Conclusion:**
- The compound that is **not an isomer of pentanal** is **3-Methyl-2-butanol** because it has a different functional group (alcohol instead of aldehyde) and a different molecular formula.

### Final Answer:
**3-Methyl-2-butanol is not an isomer of pentanal.**