Which one of the following compounds on dehalogenation gives, 2,3 - dimethyl - but - 2 - ene ?

Options

A. `CH_3-underset(CH_3)underset(|)overset(Cl)overset(|)C-underset(CH_3)underset(|)overset(Cl)overset(|)C-CH_3`
B. `CH_3-(CH_2)_4-CHCl_2`
C. `CH_3-CH_2-CHCl_2`
D. `CH_2Cl-(CH_2)_4-CH_2Cl`

Answer

To solve the question of which compound on dehalogenation gives 2,3-dimethylbut-2-ene, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dehalogenation**:
- Dehalogenation refers to the removal of halogen atoms (like Cl, Br) from a compound. In this case, we are looking for a compound that, when two halogen atoms are removed, will yield 2,3-dimethylbut-2-ene.

2. **Identifying the Target Compound**:
- The target compound is 2,3-dimethylbut-2-ene. This compound has a double bond between the second and third carbon atoms and two methyl groups attached to the second and third carbon.

3. **Analyzing the Structure of 2,3-Dimethylbut-2-ene**:
- The structure can be represented as follows:
```
CH3
|
CH3-C=C-CH3
```
- This indicates that the compound must have two halogen atoms that can be removed to form the double bond.

4. **Determining the Possible Dihalide Alkane**:
- To obtain 2,3-dimethylbut-2-ene from dehalogenation, the starting compound must be a dihalide that has two halogen atoms on adjacent carbons (specifically, the second and third carbons).
- A suitable candidate would be 2,3-dichloro-2,3-dimethylbutane, which has the following structure:
```
CH3
|
Cl-C-Cl
|
CH3
```

5. **Performing Dehalogenation**:
- When 2,3-dichloro-2,3-dimethylbutane undergoes dehalogenation (for example, with zinc), the two Cl atoms are removed, leading to the formation of the double bond between the second and third carbon atoms, resulting in 2,3-dimethylbut-2-ene.

6. **Conclusion**:
- Therefore, the compound that gives 2,3-dimethylbut-2-ene upon dehalogenation is 2,3-dichloro-2,3-dimethylbutane.

### Final Answer:
The compound that gives 2,3-dimethylbut-2-ene upon dehalogenation is **2,3-dichloro-2,3-dimethylbutane**.