Primary halides follow the mechanism:

Options

A. `S_(N)` 1
B. `S_(N)`2
C. Both (1) and (2)
D. None of these

Answer

To determine the mechanism followed by primary halides, we will analyze the characteristics of primary alkyl halides and the two types of nucleophilic substitution mechanisms: SN1 and SN2.

### Step-by-Step Solution:

1. **Identify Primary Halides**:
- A primary halide is an alkyl halide where the carbon atom bonded to the halogen is attached to only one other carbon atom.
- Example: Ethyl bromide (CH3CH2Br) is a primary halide.

**Hint**: Remember that primary halides have the halogen attached to a primary carbon, which is only connected to one other carbon.

2. **Understand SN1 and SN2 Mechanisms**:
- **SN1 Mechanism**:
- This is a two-step mechanism involving the formation of a carbocation intermediate.
- The rate of the reaction depends on the stability of the carbocation formed. More stable carbocations (tertiary > secondary > primary) will favor this mechanism.
- **SN2 Mechanism**:
- This is a one-step mechanism where the nucleophile attacks the substrate as the leaving group departs.
- The rate of the reaction is influenced by steric hindrance; less hindered substrates (like primary halides) favor this mechanism.

**Hint**: SN1 is favored by stable carbocations, while SN2 is favored by less sterically hindered environments.

3. **Analyze Stability of Carbocations**:
- For primary halides, the carbocation formed (if SN1 were to occur) would be a primary carbocation, which is not stable.
- Therefore, primary halides do not favor the SN1 mechanism due to the instability of the primary carbocation.

**Hint**: Recall that primary carbocations are less stable compared to secondary and tertiary carbocations.

4. **Determine the Preferred Mechanism for Primary Halides**:
- Since primary halides do not form stable carbocations, they cannot proceed via the SN1 mechanism.
- Instead, they undergo the SN2 mechanism, where the nucleophile attacks the carbon atom directly, leading to the substitution of the halogen.

**Hint**: Focus on the fact that primary halides are less hindered, making them ideal candidates for the SN2 mechanism.

5. **Conclusion**:
- Primary halides predominantly follow the SN2 mechanism due to the instability of the primary carbocation and the low steric hindrance that allows the nucleophile to approach easily.

**Final Answer**: Primary halides follow the SN2 mechanism.