Alcohols react with HCL or `PCL_(5)` , but phenol does not Why ?

Explanation

To answer the question of why alcohols react with HCl or PCl5 while phenols do not, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Structures**:
- Alcohols have the general formula \( R-OH \) where \( R \) is an alkyl group.
- Phenols have the structure \( C_6H_5-OH \) where the hydroxyl group (-OH) is attached to a benzene ring.

2. **Resonance in Phenols**:
- In phenols, the lone pair of electrons on the oxygen atom can participate in resonance with the π electrons of the benzene ring. This means that the electron density is delocalized over the ring, which stabilizes the structure.

3. **Bond Character**:
- Due to resonance, the carbon-oxygen (C-O) bond in phenol exhibits some double bond character. This makes the bond stronger and less reactive towards nucleophiles such as halide ions (from HCl or PCl5).

4. **Comparison with Alcohols**:
- In contrast, the C-O bond in alcohols is purely a single bond and does not have the same resonance stabilization. This makes the C-O bond in alcohols weaker and more susceptible to cleavage by nucleophiles.

5. **Reactivity with Halides**:
- Alcohols can easily be protonated in the presence of an acid (like HCl), forming a better leaving group (water) and allowing the nucleophile (halide ion) to attack and replace the hydroxyl group.
- Phenols, due to their resonance and the partial double bond character of the C-O bond, do not undergo this reaction as readily. The bond is not easily cleaved by halide ions.

6. **Conclusion**:
- Therefore, alcohols react with HCl or PCl5 because their C-O bond is a weak single bond, while phenols do not react under the same conditions due to the stronger C-O bond with partial double bond character resulting from resonance.