Electrophilic substitution in benzene is a type of chemical reaction in which an atom or group of atoms on the benzene ring is replaced by another atom or group without disturbing the ring’s aromatic stability.
Here’s a clear breakdown:
- Benzene is stable due to its delocalized electrons (aromaticity), so it doesn’t easily react like ordinary alkenes.
- In electrophilic substitution, a strong electrophile (an electron-seeking species) attacks the benzene ring.
- This attack temporarily disrupts the aromatic electron cloud, forming an intermediate called a sigma complex or arenium ion.
- A proton (hydrogen ion) is then removed from the intermediate, restoring the aromaticity of the ring.
Examples of electrophilic substitution reactions in benzene include:
- Halogenation (replacing a hydrogen with Cl or Br)
- Nitration (replacing a hydrogen with –NO₂)
- Sulfonation (replacing a hydrogen with –SO₃H)
- Friedel-Crafts alkylation and acylation (replacing a hydrogen with an alkyl or acyl group)
Key points:
- The aromaticity of benzene is preserved.
- The reaction involves electrophiles, not nucleophiles.
- Benzene is less reactive than alkenes due to its stable electron cloud.