`3^(@)` alkyl halides form alcohols preferably via

Options

A. `S_(N)2`
B. `S_(N)1`
C. Transition state
D. `S_(N)2i`

Explanation

To determine how tertiary alkyl halides form alcohols, we need to analyze the mechanisms of nucleophilic substitution reactions. Here’s a step-by-step solution to the question:

### Step 1: Identify the Structure of Tertiary Alkyl Halides
Tertiary alkyl halides have the general structure R3C-X, where R represents alkyl groups and X is a halogen (like Cl, Br, or I). For example, consider the tertiary alkyl halide tert-butyl chloride (C(CH3)3Cl).

**Hint:** Tertiary alkyl halides have three alkyl groups attached to the carbon that is bonded to the halogen.

### Step 2: Understand the Mechanisms of Nucleophilic Substitution
There are two primary mechanisms for nucleophilic substitution:
- **SN1 Mechanism:** Involves two steps: formation of a carbocation intermediate followed by nucleophilic attack.
- **SN2 Mechanism:** Involves a single concerted step where the nucleophile attacks the substrate as the leaving group departs.

**Hint:** Remember that SN1 is a two-step process, while SN2 is a one-step process.

### Step 3: Analyze the SN1 Mechanism
In the SN1 mechanism:
1. The leaving group (halide ion) departs first, forming a stable carbocation.
2. The nucleophile (OH-) then attacks the carbocation to form the alcohol.

For tertiary alkyl halides, the carbocation formed is stable due to the +I effect of the three alkyl groups, which help stabilize the positive charge.

**Hint:** Tertiary carbocations are stabilized by surrounding alkyl groups, making the SN1 pathway favorable.

### Step 4: Analyze the SN2 Mechanism
In the SN2 mechanism:
1. The nucleophile attacks the carbon from the opposite side of the leaving group, leading to a transition state.
2. The leaving group departs, resulting in the formation of the alcohol.

However, for tertiary alkyl halides, steric hindrance from the bulky alkyl groups makes it difficult for the nucleophile to approach the carbon atom effectively. This results in an unstable transition state.

**Hint:** Steric hindrance in tertiary alkyl halides prevents the SN2 mechanism from occurring efficiently.

### Step 5: Conclusion
Given that tertiary alkyl halides form stable carbocations and the steric hindrance prevents the SN2 mechanism, we conclude that tertiary alkyl halides preferentially form alcohols via the **SN1 mechanism**.

**Final Answer:** Tertiary alkyl halides form alcohols preferably via **SN1** mechanism (Option B).