Question

Write the resonance structures of chlorobenzene and explain.

Answer 1

1. Chlorobenzene (C₆H₅Cl) consists of a benzene ring with a chlorine atom attached to it.
2. The benzene ring has a delocalized π-electron system, which can overlap with the lone pair of electrons on the chlorine atom.
3. This leads to resonance, where the lone pair on chlorine participates in conjugation with the π-electrons of the benzene ring.
4. As a result, multiple resonance structures are formed, showing electron delocalization over the ring.
5. In the resonance structures: 
   • A double bond forms between chlorine and the ring.
   • Negative charges appear at the ortho and para positions of the ring.
6. There are four main resonance structures: 
   • One is the original structure with a normal C–Cl single bond and alternating double bonds in the ring.
   • Three others show the delocalization of electrons, with a partial double bond between carbon and chlorine, and negative charges on ortho and para carbon atoms.
7. The C–Cl bond in chlorobenzene has partial double bond character, making it stronger and shorter than a typical C–Cl bond.
8. Due to resonance, electron density increases at the ortho and para positions of the ring.
9. This makes chlorobenzene more reactive towards electrophilic substitution at ortho and para positions.
10. However, the C–Cl bond becomes less reactive towards nucleophilic substitution due to its partial double bond character.

•