Which of the following is NOT an isomer of hexane ?

Options

A. 2-Methylpentane
B. 2,2-Dimethylbutane
C. 2,2 -Dimethylpentane
D. 3- Methylpentane

Answer

To determine which of the following compounds is NOT an isomer of hexane, we need to analyze each option provided. The options are:

1. 2-methylpentane
2. 2,2-dimethylbutane
3. 2,2-dimethylpentane
4. 3-methylpentane

Hexane (C6H14) has a total of 6 carbon atoms. An isomer is a compound that has the same molecular formula but a different structure.

### Step-by-step Solution:

**Step 1: Analyze 2-methylpentane**
- Structure: 2-methylpentane has 5 carbon atoms in the main chain and 1 carbon atom as a branch.
- Total carbon count: 5 (from pentane) + 1 (methyl group) = 6
- Conclusion: 2-methylpentane is an isomer of hexane.

**Step 2: Analyze 2,2-dimethylbutane**
- Structure: 2,2-dimethylbutane has 4 carbon atoms in the main chain and 2 carbon atoms as branches.
- Total carbon count: 4 (from butane) + 2 (two methyl groups) = 6
- Conclusion: 2,2-dimethylbutane is an isomer of hexane.

**Step 3: Analyze 2,2-dimethylpentane**
- Structure: 2,2-dimethylpentane has 5 carbon atoms in the main chain and 2 carbon atoms as branches.
- Total carbon count: 5 (from pentane) + 2 (two methyl groups) = 7
- Conclusion: 2,2-dimethylpentane is NOT an isomer of hexane because it has 7 carbon atoms, while hexane has only 6.

**Step 4: Analyze 3-methylpentane**
- Structure: 3-methylpentane has 5 carbon atoms in the main chain and 1 carbon atom as a branch.
- Total carbon count: 5 (from pentane) + 1 (methyl group) = 6
- Conclusion: 3-methylpentane is an isomer of hexane.

### Final Answer:
The compound that is NOT an isomer of hexane is **2,2-dimethylpentane**.

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