Which of the following convert a primary hydroxyl group into good leaving group for a `S_(N)2` reaction ?

Options

A.
B.
C. `PCl_(5)`
D. Nal (5 molar solution )

Explanation

To convert a primary hydroxyl group into a good leaving group for an \( S_N2 \) reaction, we need to consider various reagents that can facilitate this transformation. Here’s a step-by-step solution to identify which reagents can achieve this:

### Step 1: Understand the Primary Hydroxyl Group
A primary hydroxyl group (–OH) is present in primary alcohols. In order to participate in an \( S_N2 \) reaction, the hydroxyl group must be converted into a better leaving group, such as a halide ion (Cl⁻, Br⁻, or I⁻).

**Hint:** Recall that a good leaving group is typically a stable ion or molecule that can depart easily during a reaction.

### Step 2: Analyze the Given Reagents
We will examine each of the given reagents to see if they can convert the primary hydroxyl group into a good leaving group.

1. **Reagent A: HCl (Hydrochloric Acid)**
- When HCl reacts with a primary alcohol, it protonates the hydroxyl group, converting it into water (H₂O), which is a good leaving group.
- The reaction can be represented as:
\[ RCH_2OH + HCl \rightarrow RCH_2Cl + H_2O \]
- **Conclusion:** This reagent is effective in converting the hydroxyl group into a good leaving group.

**Hint:** Consider how protonation of the hydroxyl group affects its ability to leave.

2. **Reagent B: SOCl₂ (Thionyl Chloride)**
- SOCl₂ reacts with primary alcohols to convert the hydroxyl group into a chloride. The reaction involves the formation of an intermediate that eventually leads to the release of HCl and the formation of a good leaving group.
- The reaction can be represented as:
\[ RCH_2OH + SOCl_2 \rightarrow RCH_2Cl + SO_2 + HCl \]
- **Conclusion:** This reagent also effectively converts the hydroxyl group into a good leaving group.

**Hint:** Look for reagents that can replace the hydroxyl group with a halide.

3. **Reagent C: PCl₅ (Phosphorus Pentachloride)**
- PCl₅ can convert the hydroxyl group into a chloride by replacing the –OH group with a –Cl group, forming a good leaving group.
- The reaction can be represented as:
\[ RCH_2OH + PCl_5 \rightarrow RCH_2Cl + POCl_3 + HCl \]
- **Conclusion:** This reagent is also effective in converting the hydroxyl group into a good leaving group.

**Hint:** Consider the role of phosphorus compounds in halogenation reactions.

4. **Reagent D: NaI (Sodium Iodide)**
- Sodium iodide reacts with primary alcohols but does not convert the hydroxyl group into a good leaving group. Instead, it forms an alkoxide (–O⁻Na⁺), which is not a good leaving group in \( S_N2 \) reactions.
- The reaction can be represented as:
\[ RCH_2OH + NaI \rightarrow RCH_2O^-Na^+ + HI \]
- **Conclusion:** This reagent does not effectively convert the hydroxyl group into a good leaving group.

**Hint:** Consider whether the product formed is a stable leaving group or not.

### Final Answer
The reagents that convert a primary hydroxyl group into a good leaving group for an \( S_N2 \) reaction are:
- **A (HCl)**
- **B (SOCl₂)**
- **C (PCl₅)**

The correct options are A, B, and C.