Aryl Halides Reactivity

Question

Chlorobenzene is less reactive than alkyl chloride in nucleophilic substitution because:

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1. **Resonance Effect**: The lone pairs on the Chlorine atom in chlorobenzene are in conjugation with the $\pi$-electrons of the benzene ring.
2. **Bond Character**: This conjugation gives the $C-Cl$ bond a **partial double bond character**, making it shorter and much stronger than a typical $C-Cl$ single bond in alkyl halides.
3. **Hybridization**: The Carbon in chlorobenzene is $sp^2$ hybridized (more electronegative), whereas in alkyl halides it is $sp^3$. This holds the electrons tighter to the nucleus.
4. **Carbocation Instability**: For $SN1$, the phenyl cation ($C_6H_5^+$) would be very unstable due to lack of resonance stabilization.
5. **Steric/Electronic**: The $\pi$-cloud of the benzene ring also tends to repel incoming nucleophiles.

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Aryl Halides Reactivity

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