Bromination of methane in presence of sunlight is a

Options

A. nucleophilic substitution
B. free radical substitution
C. electrophilic substitution
D. nucleophilic addition

Answer

To determine the type of reaction that occurs during the bromination of methane in the presence of sunlight, we can break down the process step by step.

### Step-by-Step Solution:

1. **Identify the Reactants and Conditions**:
- The reactants are methane (CH₄) and bromine (Br₂).
- The reaction occurs in the presence of sunlight, which provides the energy needed for the reaction to proceed.

**Hint**: Look for the role of sunlight in initiating the reaction.

2. **Understand the Nature of the Reaction**:
- The reaction involves the substitution of one hydrogen atom in methane with a bromine atom, resulting in the formation of bromomethane (CH₃Br) and hydrogen bromide (HBr).

**Hint**: Identify what type of atoms or groups are being replaced in the reactants.

3. **Mechanism of the Reaction**:
- The bromination of methane proceeds through a mechanism known as free radical substitution, which consists of three main steps: initiation, propagation, and termination.

**Hint**: Familiarize yourself with the three steps of free radical mechanisms.

4. **Initiation Step**:
- In the presence of sunlight, bromine molecules undergo homolytic cleavage, producing two bromine radicals (Br•).
- Reaction: Br₂ → 2 Br•

**Hint**: Consider how energy from sunlight can break bonds in molecules.

5. **Propagation Steps**:
- In the first propagation step, a bromine radical reacts with methane, resulting in the formation of a methyl radical (CH₃•) and hydrogen bromide (HBr).
- Reaction: CH₄ + Br• → CH₃• + HBr
- In the second propagation step, the methyl radical reacts with another bromine radical to form bromomethane and regenerate a bromine radical.
- Reaction: CH₃• + Br• → CH₃Br + Br•

**Hint**: Look for the formation of radicals and how they react with each other.

6. **Termination Step**:
- The reaction can terminate when two radicals combine to form a stable product, such as two bromine radicals forming bromine or two methyl radicals forming ethane.
- Reaction: Br• + Br• → Br₂ or CH₃• + CH₃• → C₂H₆

**Hint**: Think about how radicals can combine to stop the chain reaction.

7. **Conclusion**:
- Since the reaction involves the substitution of a hydrogen atom by a bromine atom through a radical mechanism, the correct classification of the reaction is free radical substitution.

**Final Answer**: The bromination of methane in the presence of sunlight is a **free radical substitution** reaction (Option 2).