What is the major product of the following reaction ? `CH_(3)C-=C-CH_(2)-CH_(3)underset(underset("catalyst")(Cl_(2)))overset("1 mole of")rarr`?

Options

A.
B. `CH_3CH_2-underset(Cl)underset(|)overset(Cl)overset(|)C-CH_2CH_3`
C. `CH_3-underset(Cl)underset(|)overset(Cl)overset(|)C-CH_2-CH_2-CH_3`
D.

Answer

To determine the major product of the reaction between 1-mole of Cl2 and the alkyne CH3C≡CCH2CH3 in the presence of a catalyst, we can follow these steps:

### Step 1: Identify the Reactants
The reactants are:
- An alkyne: CH3C≡CCH2CH3 (which is 2-pentyne)
- Chlorine (Cl2) in the presence of a catalyst.

### Step 2: Understand the Reaction Type
The reaction involves the addition of chlorine to the alkyne. Since we are using 1 mole of Cl2, we expect the reaction to add chlorine across the triple bond.

### Step 3: Mechanism of the Reaction
1. **Formation of Chloronium Ion**:
- The Cl2 molecule approaches the triple bond of the alkyne. The π electrons of the triple bond attack one of the chlorine atoms, resulting in the formation of a cyclic chloronium ion. This intermediate has a positive charge on one of the carbons.

2. **Nucleophilic Attack**:
- The other chlorine atom, which is now negatively charged, attacks the more stable carbocation formed from the chloronium ion. This attack occurs from the opposite side of the chloronium ion due to steric hindrance, leading to an anti-addition.

### Step 4: Determine the Product
The product formed from this reaction is a trans-alkene. Specifically, the structure will have the two chlorine atoms added to the carbon atoms that were originally part of the triple bond, resulting in a trans configuration.

### Step 5: Write the Final Product
The final product can be represented as:
- CH3C(Cl)=C(Cl)CH2CH3

This indicates that we have a trans-2,3-dichloropentene.

### Conclusion
The major product of the reaction is trans-2,3-dichloropentene.