When HBr adds to 1-butene in the presence of benzoyl peroxide, the product obtained is

Options

A. 1-Bromobutene
B. 2-Bromobutene
C. 1-Bromobutane
D. 2-Bromobutane

Answer

To solve the question about the product obtained when HBr adds to 1-butene in the presence of benzoyl peroxide, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants are 1-butene (C4H8) and HBr (hydrobromic acid).
- Benzoyl peroxide (C14H10O4) is used as a radical initiator.

2. **Understand the Reaction Mechanism**:
- The presence of benzoyl peroxide indicates that the reaction will proceed via a free radical mechanism. This is different from the usual electrophilic addition.

3. **Initiation Step**:
- Benzoyl peroxide undergoes homolytic cleavage to form two benzoyloxy radicals (C6H5C(O)O•). These radicals can further decompose to form phenyl radicals (C6H5•) and carbon dioxide.

4. **Formation of Bromine Radicals**:
- The phenyl radicals can then react with HBr to generate bromine radicals (Br•) through the homolytic cleavage of HBr:
\[ \text{C}_6\text{H}_5\text{O•} + \text{HBr} \rightarrow \text{C}_6\text{H}_5\text{OH} + \text{Br•} \]

5. **Addition of Bromine Radical to 1-Butene**:
- The bromine radical (Br•) can add to 1-butene (CH2=CH-CH2-CH3). The addition can occur at either end of the double bond:
- If Br• adds to the terminal carbon (C1), it leads to a primary radical:
\[ \text{CH}_2\text{=CH-CH}_2\text{CH}_3 + \text{Br•} \rightarrow \text{CH}_2\text{Br-CH}•\text{CH}_2\text{CH}_3 \]
- If Br• adds to the second carbon (C2), it leads to a more stable secondary radical:
\[ \text{CH}_2\text{=CH-CH}_2\text{CH}_3 + \text{Br•} \rightarrow \text{CH}_3\text{CH}•\text{CH}_2\text{Br-CH}_3 \]

6. **Stability of Radicals**:
- The secondary radical (formed by Br adding to C2) is more stable than the primary radical (formed by Br adding to C1). Therefore, the secondary radical will be favored.

7. **Final Product Formation**:
- The stable secondary radical can then combine with a hydrogen atom (H•) to form the final product:
\[ \text{CH}_3\text{CH}•\text{CH}_2\text{Br-CH}_3 + \text{H•} \rightarrow \text{CH}_3\text{CH}_2\text{CHBr-CH}_3 \]
- The major product formed is 2-bromobutane.

### Conclusion:
The product obtained when HBr adds to 1-butene in the presence of benzoyl peroxide is **2-bromobutane**.