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 determine which compound on dehalogenation gives 2,3-dimethylbut-2-ene, we can follow these steps:

### Step 1: Understand the Product Structure
The target compound is 2,3-dimethylbut-2-ene. This compound has the following structure:
- It is a butene, meaning it has four carbon atoms.
- The double bond is located between the second and third carbon atoms.
- There are two methyl groups attached to the second and third carbon atoms.

### Step 2: Identify the Required Dihalide Structure
To synthesize 2,3-dimethylbut-2-ene through dehalogenation, we need a dihalide that can lead to the formation of this alkene. The dihalide must have two halogen atoms (like Cl) attached to the appropriate carbon atoms such that their removal can create the double bond.

### Step 3: Analyze the Options
We need to analyze the given options to find a dihalide that can yield the desired product upon dehalogenation.

1. **Option 1**: This option has two chlorine atoms on the second and third carbon of a four-carbon chain. When treated with zinc, this can lead to the formation of the desired alkene (2,3-dimethylbut-2-ene).

2. **Option 2**: This option has a straight chain of six carbons with two Cl on terminal carbons. This structure cannot yield a butene, so it is not the answer.

3. **Option 3**: This option has only three carbons. It cannot lead to the formation of a butene, so it is not the answer.

4. **Option 4**: This option has two chlorine atoms on terminal carbons of a straight chain. This structure cannot yield a branched alkene, so it is not the answer.

### Step 4: Conclusion
After analyzing all options, we find that **Option 1** is the only compound that can yield 2,3-dimethylbut-2-ene upon dehalogenation.

### Final Answer
The correct answer is **Option 1**.

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