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Chapter 23: Aryl Halides |
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Electrophilic Aromatic Substitution of Aryl Halides
Summary
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Aryl halides are themselves reactive towards electrophilic
aromatic substitution but they are less reactive than benzene.
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This is because halides are weak
deactivators
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Halides direct subsequent reactions ortho,
para.
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This makes them a little unusual (activators are usually ortho, para-directing,
deactivators meta-directing).
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The weak deactivation is due to the electronegativity of the halogen making
the intermediate cations less stable than those produced when benzene undergoes
substitution:
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The directing effect is due to the resonance stabilization of the cationic
intermediates derived by ortho or para attack but not
by meta attack. For example, the stabilization during ortho attack
is shown below :
