`CH_(2)=CH-CH_(2)-CH-CH_(2)overset(NBS)to[A].` The major product [A] is

Options

A. `CH_(2)=CH-underset(Br)underset(|)CH-CH=CH_(2)`
B. `CH_(2)=CH-CH=CH-CH_(2)-Br`
C. `CH_(2)=CH-underset(Br)underset(|)CH=CH_(2)`
D. `CH_(3)-underset(H)underset(|)C=C=underset(H)underset(|)C-CH_(2)-Br`

Answer

To solve the given question, we need to understand the reaction of the compound with N-bromosuccinimide (NBS) and how it leads to the formation of the major product [A]. Here’s a step-by-step breakdown of the process:

### Step 1: Identify the Reactant
The reactant is 1-pentene, which has the structure:
\[ \text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_2-\text{CH}_2 \]

### Step 2: Understand the Role of NBS
N-bromosuccinimide (NBS) is a brominating agent that generates bromine radicals when heated. The structure of NBS can be represented as:
\[ \text{NBS} = \text{C}_4\text{H}_4\text{Br}\text{N} \]
When heated, it homolytically cleaves to form a bromine radical (Br•) and a succinimide radical.

### Step 3: Radical Mechanism
1. The bromine radical (Br•) will react with the alkene (1-pentene).
2. The Br• will abstract a hydrogen atom from the most stable position on the alkene, which is typically the carbon adjacent to the double bond.

### Step 4: Formation of the Radical
When Br• abstracts a hydrogen atom from the terminal carbon (CH2), it generates a more stable radical at the second carbon (C1), leading to:
\[ \text{CH}_2=\text{C}(\text{•})-\text{CH}_2-\text{CH}_2-\text{CH}_2 \]

### Step 5: Radical Stabilization
The radical formed is stabilized by resonance. The radical can delocalize, allowing for more stability:
- The radical can be represented as:
\[ \text{CH}_2-\text{C}(\text{•})-\text{CH}_2 \]
This radical can further rearrange or react with Br•.

### Step 6: Bromination
The Br• will now react with the radical formed:
- The radical (C•) will bond with Br to form:
\[ \text{CH}_2=\text{CH}-\text{CBr}-\text{CH}_2-\text{CH}_2 \]

### Step 7: Major Product Formation
The final product after the reaction with NBS will be:
\[ \text{CH}_2=\text{CH}-\text{CBr}-\text{CH}_2-\text{CH}_2 \]
This compound is 3-bromopent-1-ene.

### Conclusion
The major product [A] formed from the reaction of 1-pentene with NBS is:
\[ \text{3-bromopent-1-ene} \]