For the preparation of `alpha` -butylene from methyl magnesium chloride, it will be reacted with

Options

A. Propene
B. Propyl chloride
C. 3–Chloro propene
D. 2–Chloro propene

Answer

To prepare alpha-butylene from methyl magnesium chloride, we need to determine the appropriate reactant that will yield this alkene. Let's go through the steps to find the correct reagent.

### Step 1: Identify the structure of alpha-butylene
Alpha-butylene is an alkene with the structure:
\[ \text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_3 \]
This can be represented as:
\[ \text{C}_4\text{H}_8 \]

### Step 2: Identify the structure of methyl magnesium chloride
Methyl magnesium chloride (a Grignard reagent) has the structure:
\[ \text{CH}_3\text{MgCl} \]
Here, the methyl group (CH₃) acts as a nucleophile.

### Step 3: Determine the reaction mechanism
In the reaction, the nucleophile (CH₃⁻ from methyl magnesium chloride) will attack an electrophilic carbon in a suitable alkyl halide to form a new carbon-carbon bond. This will lead to the formation of an alkene.

### Step 4: Consider potential reagents
We need to find a suitable alkyl halide that will react with methyl magnesium chloride to yield alpha-butylene. The options we consider are:
1. Propane
2. Propyl chloride (1-chloropropane)
3. 3-chloropropene
4. 2-chloropropene

### Step 5: Analyze each option
1. **Propyl chloride (1-chloropropane)**:
- Structure: CH₃-CH₂-CH₂Cl
- Reaction: The methyl anion attacks the carbon attached to the chlorine, leading to the formation of butane, not alpha-butylene.

2. **3-chloropropene**:
- Structure: CH₂=CH-CH₂Cl
- Reaction: The methyl anion attacks the carbon with the chlorine, resulting in the formation of alpha-butylene:
\[ \text{CH}_2=\text{CH}-\text{CH}_2\text{Cl} + \text{CH}_3^- \rightarrow \text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_3 + \text{Cl}^- \]
- This gives us the desired product, alpha-butylene.

3. **2-chloropropene**:
- Structure: CH₃-CH=CHCl
- Reaction: The methyl anion attacks the carbon with the chlorine, but this does not yield alpha-butylene.

### Step 6: Conclusion
The correct reagent to react with methyl magnesium chloride to prepare alpha-butylene is **3-chloropropene**.

### Final Answer:
**3-chloropropene**