Which of the following is a step in the mechanism of the reaction shown?
`CH_(2)=CH-CH_(3)+HBroverset("Peroxide")tounderset(Br)underset(|)CH_(2)-CH_(2)-CH_(3)`

Options

A.
B.
C.
D.

Answer

To solve the question regarding the mechanism of the reaction between propene (CH₂=CH-CH₃) and HBr in the presence of peroxide, we can break down the steps involved in the reaction mechanism.

### Step-by-Step Solution:

1. **Initiation Step**:
- The reaction begins with the decomposition of peroxide (R₂O₂) under heat or light. This process generates two alkoxy radicals (RO•).
- **Reaction**:
\[ R_2O_2 \xrightarrow{heat/light} 2 RO• \]

**Hint**: Remember that peroxides can decompose to form radicals when exposed to heat or light.

2. **Formation of Bromine Radical**:
- The alkoxy radical (RO•) then reacts with HBr, resulting in the formation of an alcohol (ROH) and a bromine radical (Br•).
- **Reaction**:
\[ RO• + HBr \rightarrow ROH + Br• \]

**Hint**: Look for how radicals interact with other molecules to form new radicals or stable products.

3. **Propagation Step**:
- The bromine radical (Br•) reacts with the alkene (CH₂=CH-CH₃). The Br• adds to one of the carbon atoms of the double bond, forming a more stable radical intermediate.
- **Reaction**:
\[ CH_2=CH-CH_3 + Br• \rightarrow CH_2Br-CH•-CH_3 \]

**Hint**: Focus on the addition of radicals to alkenes, which often leads to the formation of stable radical intermediates.

4. **Formation of Final Product**:
- The radical intermediate (CH₂Br-CH•-CH₃) then reacts with another molecule of HBr, resulting in the final product (CH₂Br-CH₂-CH₃) and regenerating another bromine radical (Br•).
- **Reaction**:
\[ CH_2Br-CH•-CH_3 + HBr \rightarrow CH_2Br-CH_2-CH_3 + Br• \]

**Hint**: Consider how the radical intermediate can further react with HBr to yield the final product and regenerate the radical.

### Conclusion:
The mechanism involves initiation, formation of radicals, and propagation steps that lead to the final product. The correct answer to the question regarding which step is involved in the mechanism is the propagation step where the bromine radical adds to the alkene.