haloarenes

Question

Chlorobenzene is less reactive than chloroethane toward nucleophilic substitution because:

RankGuru · Accepted Answer

Haloarenes (like chlorobenzene) are remarkably unreactive toward nucleophilic substitution compared to haloalkanes due to several factors:
1. **Resonance Effect**: lone pairs on Chlorine are conjugated with the $\pi$ electrons of the benzene ring. This gives the $C-Cl$ bond **partial double bond character**, making it shorter and stronger.
2. **Hybridization**: The Carbon in $Ph-Cl$ is $sp^2$ hybridized (more electronegative), while in $R-Cl$ it is $sp^3$. The $sp^2$ carbon holds the electron pair of $C-Cl$ more tightly.
3. **Repulsion**: The electron-rich benzene ring repels incoming nucleophiles.
4. **Phenyl Cation Instability**: $S_N1$ is impossible as the phenyl cation is highly unstable.

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haloarenes

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