The reaction , `CH_(3)Br +OH^(-)rarrCH_(3)OH+Br^(-)` obeys the mechanism

Options

A. `S_(N^(1))`
B. `S_(N^(2))`
C. `E_(1)`
D. `E_(2)`

Answer

To determine the mechanism of the reaction `CH₃Br + OH⁻ → CH₃OH + Br⁻`, we will analyze the characteristics of the reaction and the mechanisms involved.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are methyl bromide (CH₃Br) and hydroxide ion (OH⁻).
- The products are methanol (CH₃OH) and bromide ion (Br⁻).

2. **Classify the Reaction**:
- This is a nucleophilic substitution reaction where a nucleophile (OH⁻) replaces a leaving group (Br⁻) in the alkyl halide (CH₃Br).

3. **Consider the Mechanisms**:
- The two main mechanisms for nucleophilic substitution are SN1 and SN2.
- SN1 involves the formation of a carbocation intermediate, while SN2 involves a single concerted step where the nucleophile attacks the substrate.

4. **Evaluate SN1 Mechanism**:
- In an SN1 mechanism, the first step is the formation of a carbocation (CH₃⁺) after the leaving group (Br⁻) departs.
- However, methyl carbocation (CH₃⁺) is highly unstable due to the lack of alkyl groups to stabilize the positive charge.

5. **Evaluate SN2 Mechanism**:
- In an SN2 mechanism, the nucleophile (OH⁻) attacks the carbon atom of CH₃Br from the opposite side of the leaving group (Br⁻), leading to a transition state.
- This results in the direct displacement of Br⁻ and the formation of methanol (CH₃OH) in a single step.

6. **Determine the Correct Mechanism**:
- Since CH₃Br cannot form a stable carbocation and the reaction involves a direct attack by the nucleophile, the mechanism that best describes this reaction is SN2.
- Therefore, the correct answer is **Option B: SN2**.