Electrophilic substitution

Electrophilic substitution is a reaction in which an electrophile replaces an atom or group in a molecule. In aromatic substitution, it commonly replaces hydrogen while the ring regains its aromaticity.

Electrophilic aromatic substitution: A reaction in which an electrophile replaces a hydrogen on an aromatic ring. This common form proceeds through a temporary loss and restoration of aromaticity.
Nitration: A reaction that introduces a nitro group into an organic molecule. Aromatic nitration installs a nitro group through electrophilic substitution.
Benzene: A six-carbon aromatic hydrocarbon with a planar ring and six delocalized pi electrons. It is the standard substrate used to introduce the substitution mechanism.
Nucleophilic aromatic substitution: A reaction in which a nucleophile replaces a leaving group on an aromatic ring. It reverses the roles of attacking species and departing group.
Arenium ion: A resonance-stabilized carbocation formed when an electrophile bonds to an aromatic ring. It is the nonaromatic intermediate formed before a proton leaves.
Sulfonation: A reaction that introduces a sulfonic acid or sulfonyl group into a compound. Aromatic sulfonation is reversible and provides a temporary directing group.
Resonance: A model representing delocalized electrons with multiple contributing Lewis structures. Resonance describes stabilization of both aromatic rings and arenium-ion intermediates.
Electrophilic addition: A reaction in which an electrophile adds across a multiple bond, reducing its bond order. Unlike addition, aromatic substitution ultimately restores the ring's conjugation.
Aromaticity: The extra stability associated with cyclic, conjugated systems that satisfy aromatic electron-counting rules. The reaction restores this stabilization by removing a proton from the intermediate.
Halogenation: A reaction that introduces one or more halogen atoms into a compound. Aromatic halogenation uses an activated halogen electrophile to replace ring hydrogen.

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HaloalkaneCompared with: This substitution pathway contrasts with nucleophilic replacement of halide in haloalkanes.