Electrophilic Aromatic Substitution (EAS) is a type of chemical reaction in which an electrophile replaces a hydrogen atom on an aromatic ring without disturbing the ring’s stability.
Key Points (Simple Version):
- Why it happens:
- Aromatic rings (like benzene) are very stable.
- They don’t like addition reactions because adding something would break the stable electron system.
- So, they undergo substitution reactions instead—replacing a hydrogen while keeping the ring intact.
- Steps of EAS:
a) Electrophile formation: The attacking species (electrophile) is generated.
b) Attack on the ring: The electrophile temporarily bonds to the ring, forming a non-aromatic intermediate.
c) Restoration of aromaticity: A hydrogen is removed from the carbon that reacted, restoring the aromatic ring. - Common EAS reactions:
- Nitration: Introduce –NO₂ group
- Sulfonation: Introduce –SO₃H group
- Halogenation: Introduce –Cl or –Br
- Friedel–Crafts alkylation/acylation: Introduce –R or –COR group
Example (Simple):
Benzene + Br₂ → Bromobenzene (with FeBr₃ as a catalyst)
- Bromine (Br⁺) attacks benzene, one H is replaced by Br, aromaticity is preserved.
In short: Electrophilic aromatic substitution is replacing a hydrogen on a benzene ring with an electrophile without destroying the ring’s stability.