Chlorobenzene is resistant to nucleophilic substitution due to the electron-withdrawing effect of the chlorine atom, which decreases the electron density on the benzene ring. This makes the carbon attached to the chlorine less electrophilic, which reduces its ability to undergo nucleophilic attack. Additionally, the resonance stabilization of the chlorine atom with the aromatic ring further makes the carbon-chlorine bond stronger, thus making nucleophilic substitution less favorable.
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