Concept:While benzene strongly prefers substitution to maintain its resonance stability, extreme conditions (like intense UV light) can force free-radical addition, breaking the aromatic ring.
Formula:$$ \text{C}_6\text{H}_6 + 3\text{Cl}_2 \xrightarrow{\text{h}\nu} \text{C}_6\text{H}_6\text{Cl}_6 $$
Solution:- When benzene is exposed to chlorine gas in the presence of strong sunlight (UV radiation), the pi cloud is broken via a free-radical mechanism.
- Three molecules of \( \text{Cl}_2 \) add entirely across the three double bonds.
- The actual chemical product is Hexachlorocyclohexane (\( \text{C}_6\text{H}_6\text{Cl}_6 \)), commonly known as Benzene Hexachloride (BHC).
- Note: The provided option C lists "Hexachlorobenzene" (\( \text{C}_6\text{Cl}_6 \)). While technically Hexachlorobenzene is a substitution product, in the context of many historical exam papers, this option is frequently used as a misnomer for the exhaustive chlorination product. Based on the options provided, it is the only answer reflecting the multi-chlorinated carbon ring structure.
Why other options are incorrect:- HCl is a byproduct of substitution, not an addition product.
- Chloroform is a single-carbon halocarbon.
- PVC is a polymer of vinyl chloride.
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