Which of the following reactions are completed through free radical intermediate ?

Options

A. `(CH_3)_3CH+Br_2overset(hv)to (CH_3)_3 CBr+HBr`
B. `(CH_3)_3C=CH_2+Br_2 to CH_3-undersetunderset(CH_3)(|)overset(Br)overset(|)C-oversetoverset(Br)(|)CH_2`
C. `CH_3-CH=CH_2+Cl_2overset(hv)to undersetunderset(Cl)(|)CH_2-CH=CH_2`
D. `Ph-CH=CH_2+HBr underset(hv)overset(R_2O_2)to Ph-CH_2-undersetunderset(Br)(|)CH_2`

Answer

To determine which reactions are completed through free radical intermediates, we will analyze each of the given reactions step by step.

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions to analyze.
- Reaction 1: Bromination in the presence of light
- Reaction 2: Electrophilic addition on alkene
- Reaction 3: Chlorination in the presence of light
- Reaction 4: Another reaction involving hydrogen peroxide and light

2. **Analyze Reaction 1 (Bromination in presence of light)**:
- This reaction involves the bromine molecule (Br2) undergoing homolytic cleavage due to the presence of light, forming two bromine radicals (Br•).
- These bromine radicals can then react with alkanes to form alkyl bromides.
- **Conclusion**: This reaction proceeds through a free radical mechanism.

**Hint**: Look for the presence of light and homolytic cleavage in the mechanism.

3. **Analyze Reaction 2 (Electrophilic addition on alkene)**:
- This reaction involves the addition of electrophiles to alkenes, typically resulting in the formation of cyclic intermediates (like bromonium ions).
- There is no free radical formation in this process.
- **Conclusion**: This reaction does not proceed through a free radical mechanism.

**Hint**: Electrophilic addition typically involves cyclic intermediates rather than free radicals.

4. **Analyze Reaction 3 (Chlorination in presence of light)**:
- Similar to bromination, chlorination in the presence of light involves the homolytic cleavage of Cl2 to form chlorine radicals (Cl•).
- These radicals can then react with alkanes to produce alkyl chlorides.
- **Conclusion**: This reaction proceeds through a free radical mechanism.

**Hint**: Check for the presence of light and radical formation from diatomic molecules.

5. **Analyze Reaction 4 (Reaction with hydrogen peroxide and light)**:
- This reaction involves the cleavage of a double bond in the presence of hydrogen peroxide and light, leading to the formation of free radicals.
- The presence of light causes the homolytic cleavage of bonds, resulting in radical intermediates.
- **Conclusion**: This reaction proceeds through a free radical mechanism.

**Hint**: The presence of hydrogen peroxide and light often indicates a free radical pathway.

### Final Conclusion:
The reactions that proceed through free radical intermediates are:
- Reaction 1: Bromination in presence of light
- Reaction 3: Chlorination in presence of light
- Reaction 4: Reaction with hydrogen peroxide and light

**Answer**: Reactions 1, 3, and 4 are completed through free radical intermediates.