How does sodium hydroxide react with chlorobenzene?
Electron withdrawing groups activate the benzene ring to nucleophilic attack.
NaOH does react with chlorobenzene, but only under extreme conditions.
Aryl halides cannot undergo an
Electron withdrawing groups ortho and para to the leaving group activate the ring to nucleophilic attack. The more electron withdrawing groups you have, the faster the reaction becomes.
For example, the relative rates for reaction with NaOH are:
4-Nitrochlorobenzene: 7 × 10¹⁰
2,4-Dinitrochlorobenzene: 2.4 × 10¹⁵
2,4,6-Trinitrochlorobenzene: Too fast to measure
The reaction goes by a two-step
Step 1 is an addition. Step 2 is an elimination reaction. So this is an addition-elimination reaction.
Step 1: Addition
Consider the reaction of 2,4-dinitrochlorobenzene with aqueous NaOH.
OH⁻ attacks the ipso carbon (the carbon bearing the leaving group). This destroys the aromaticity of the ring. But it forms a resonance-stabilized σ-complex in which the negative charge is delocalized around the ring and the O atoms of the nitro groups.
Step 2: Loss of the leaving group
The Cl⁻ leaves, regenerating the aromatic π system.
The video below describes the nucleophilic aromatic substitution mechanism.