Question

Explain why:

Haloarenes undergo electrophilic substitution at o- and p-positions and not at m-positions.

Answer 1

1. Haloarenes contain a halogen atom (like Cl, Br, I) attached to an aromatic ring.
2. Halogens are electronegative, so they withdraw electron density from the ring via the inductive effect (–I effect), which makes the ring less reactive overall.
3. However, halogens also have lone pairs, which they donate to the ring through resonance (+R effect).
4. This resonance increases electron density specifically at the ortho and para positions of the ring.
5. As a result, electrophiles prefer to attack these electron-rich positions (ortho and para).
6. The meta position does not benefit from resonance and remains electron-deficient.

Therefore, electrophilic substitution reactions occur mainly at ortho and para positions, not at meta.