Which alcohol is most reactive towards `HCl` in the presence of anhydrous `ZnCl_(2)`?

Options

A.
B.
C.
D.

Explanation

To determine which alcohol is most reactive towards HCl in the presence of anhydrous ZnCl₂ (Lucas reagent), we need to analyze the stability of the carbocations formed during the reaction. Here’s a step-by-step solution:

### Step 1: Identify the Alcohols
We have two benzylic alcohols to consider:
1. Benzylic alcohol (C₆H₅-CH₂OH)
2. Chlorosubstituted benzylic alcohol (C₆H₄Cl-CH₂OH, where Cl is at the meta position)

### Step 2: Understand the Reaction
The reaction of alcohols with HCl in the presence of ZnCl₂ leads to the formation of carbocations. The stability of these carbocations will determine the reactivity of the alcohols.

### Step 3: Determine Carbocation Stability
- **Benzylic Alcohol (C₆H₅-CH₂OH)**: When this alcohol reacts, it forms a benzylic carbocation (C₆H₅-CH₂⁺). This carbocation is stabilized by resonance with the aromatic ring.

- **Chlorosubstituted Benzylic Alcohol (C₆H₄Cl-CH₂OH)**: When this alcohol reacts, it forms a carbocation (C₆H₄Cl-CH₂⁺). However, the presence of the chlorine atom at the meta position exerts a -I (inductive) effect, which pulls electron density away from the carbocation, making it less stable.

### Step 4: Compare the Stability
The benzylic carbocation formed from the first alcohol is more stable due to resonance stabilization from the aromatic ring. In contrast, the carbocation formed from the chlorosubstituted alcohol is destabilized by the -I effect of the chlorine atom.

### Step 5: Conclusion
Since the stability of the carbocation is crucial for the reactivity of the alcohols, the benzylic alcohol (C₆H₅-CH₂OH) is more reactive towards HCl in the presence of anhydrous ZnCl₂ compared to the chlorosubstituted benzylic alcohol.

### Final Answer
The most reactive alcohol towards HCl in the presence of anhydrous ZnCl₂ is **benzylic alcohol (C₆H₅-CH₂OH)**.

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