Which of the following is not functional group isomer of cyclopentanone.

Options

A.
B.
C.
D.

Explanation

To determine which of the following compounds is not a functional group isomer of cyclopentanone, we need to analyze the molecular formula and structure of cyclopentanone and compare it with the other given compounds.

### Step-by-step Solution:

1. **Identify the Molecular Formula of Cyclopentanone**:
- Cyclopentanone has the following structure:
- It is a cyclic ketone with 5 carbon atoms and 1 oxygen atom.
- The molecular formula is \( C_5H_8O \).

2. **Understanding Functional Group Isomers**:
- Functional group isomers are compounds that have the same molecular formula but different functional groups.
- To find functional group isomers of cyclopentanone, we need to check if the other compounds have the same molecular formula \( C_5H_8O \) and different functional groups.

3. **Analyze Each Compound**:
- **Compound 1**:
- Structure: Contains a hydroxyl group (-OH) and a double bond (alkene).
- Count: 5 carbons, 8 hydrogens, 1 oxygen.
- Molecular formula: \( C_5H_8O \) (Functional group: Alcohol).
- Conclusion: This is a functional group isomer.

- **Compound 2**:
- Structure: Contains an aldehyde functional group.
- Count: 5 carbons, 8 hydrogens, 1 oxygen.
- Molecular formula: \( C_5H_8O \) (Functional group: Aldehyde).
- Conclusion: This is a functional group isomer.

- **Compound 3**:
- Structure: Contains an ether functional group.
- Count: 5 carbons, 8 hydrogens, 1 oxygen.
- Molecular formula: \( C_5H_8O \) (Functional group: Ether).
- Conclusion: This is a functional group isomer.

- **Compound 4**:
- Structure: Contains a hydroxyl group (-OH) but has a different arrangement leading to more hydrogens.
- Count: 5 carbons, 10 hydrogens, 1 oxygen.
- Molecular formula: \( C_5H_{10}O \) (Different from cyclopentanone).
- Conclusion: This is not a functional group isomer since it does not have the same molecular formula.

4. **Final Conclusion**:
- The compound that does not qualify as a functional group isomer of cyclopentanone is the last one (Compound 4).
- Therefore, the answer is **Option D**.