Which of the following alkene gives four monochloro (structural isomer) products after hydrogenation ?

Options

A. Pent-2-ene
B. 2-Methylbut-2-ene
C. 3-Methylhex-2-ene
D. 2,3-dimethyl-but-2-ene

Answer

To determine which alkene gives four monochloro structural isomers after hydrogenation, we need to analyze each of the given alkenes step by step.

### Step 1: Identify the Alkenes
We have four alkenes to consider:
1. Pent-2-ene
2. 2-Methylbut-2-ene
3. 3-Methylhex-2-ene
4. 2,3-Dimethylbut-2-ene

### Step 2: Analyze Each Alkene

**Alkene 1: Pent-2-ene**
- Structure: CH3-CH=CH-CH2-CH3
- Types of Carbons:
- 1st type: CH3 (2 positions)
- 2nd type: CH (1 position)
- 3rd type: CH2 (1 position)
- Total types of carbon: 3
- Possible monochloro products: 3 structural isomers.

**Conclusion for Alkene 1:** It gives only 3 monochloro isomers.

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**Alkene 2: 2-Methylbut-2-ene**
- Structure: CH3-C(CH3)=CH-CH3
- Types of Carbons:
- 1st type: CH3 (3 positions)
- 2nd type: CH (1 position)
- Total types of carbon: 4
- Possible monochloro products: 4 structural isomers.

**Conclusion for Alkene 2:** It gives 4 monochloro isomers.

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**Alkene 3: 3-Methylhex-2-ene**
- Structure: CH3-CH(CH3)-CH=CH-CH2-CH3
- Types of Carbons:
- 1st type: CH3 (2 positions)
- 2nd type: CH (2 positions)
- 3rd type: CH2 (2 positions)
- Total types of carbon: 5
- Possible monochloro products: More than 4 structural isomers.

**Conclusion for Alkene 3:** It gives more than 4 monochloro isomers.

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**Alkene 4: 2,3-Dimethylbut-2-ene**
- Structure: CH3-C(CH3)=C(CH3)-CH3
- Types of Carbons:
- 1st type: CH3 (4 positions)
- 2nd type: CH (1 position)
- Total types of carbon: 3
- Possible monochloro products: 3 structural isomers.

**Conclusion for Alkene 4:** It gives only 3 monochloro isomers.

### Final Conclusion
The alkene that gives four monochloro structural isomers after hydrogenation is **2-Methylbut-2-ene**.