In the given reaction
`CH_(3)-underset(CH_(3))underset("| ")"CH"-CH=CH_(2)+HCl rarr [X]`
Major product [X] will be

Options

A. 2 - chloro -3- methylbutane
B. 1 - chloro -3- methylbutane
C. 2 - chloro -2- methylbutane
D. 2 - chloropentane

Answer

To solve the given reaction, we need to determine the major product formed when 3-methyl-1-butene (CH₃-CH(CH₃)-CH=CH₂) reacts with HCl.

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactant is 3-methyl-1-butene, which has the structure CH₃-CH(CH₃)-CH=CH₂.

2. **Protonation of the Alkene**: When HCl reacts with the alkene, the double bond will undergo protonation. The H⁺ from HCl will add to one of the carbons involved in the double bond.

3. **Formation of Carbocations**:
- When H⁺ adds to the terminal carbon (C1), a 1° carbocation is formed at C2.
- When H⁺ adds to the internal carbon (C2), a more stable 2° carbocation is formed at C1.

4. **Stability of Carbocations**: The 2° carbocation is more stable than the 1° carbocation due to hyperconjugation and inductive effects. Therefore, the major pathway will favor the formation of the 2° carbocation.

5. **Carbocation Rearrangement**: The 2° carbocation can undergo rearrangement. In this case, the hydrogen from the adjacent carbon can shift to stabilize the carbocation further, leading to a more stable tertiary carbocation.

6. **Nucleophilic Attack by Cl⁻**: The Cl⁻ ion from HCl will attack the positively charged carbon of the carbocation, leading to the formation of the product.

7. **Final Product Structure**: The final product after the nucleophilic attack will be 2-chloro-2-methylbutane (CH₃-C(Cl)(CH₃)-CH₂-CH₃).

8. **IUPAC Naming**: The product can be named as 2-chloro-2-methylbutane, confirming that it is indeed the major product formed from the reaction.

### Conclusion:
The major product [X] formed from the reaction of 3-methyl-1-butene with HCl is **2-chloro-2-methylbutane**.

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