Chlorobenzene is ortho and para directing for an incoming electrophile . Explain with diagram

Question

Chlorobenzene is ortho and para directing for an incoming electrophile . Explain with diagram

Answer 1

Chlorobenzene is a substituted benzene compound where one hydrogen atom is replaced by a chlorine atom. The presence of the chlorine atom in the ring influences the reactivity of the benzene ring towards electrophilic aromatic substitution reactions.

Chlorobenzene is ortho and para directing for an incoming electrophile because of the electron-withdrawing effect of the chlorine atom. The chlorine atom is more electronegative than carbon, so it attracts electron density away from the benzene ring through inductive effects and also through resonance effects.

In the resonance structures of chlorobenzene, the negative charge on the ring is localized on the carbon atoms adjacent to the chlorine atom. This creates a partial positive charge on the carbon atoms in the ortho and para positions, making them more attractive to electrophiles.

The resonance structures of chlorobenzene can be represented as follows:

Cl Cl | | C=C C-C | | C- C-

The resonance structures show that the carbon atoms in the ortho and para positions have a partial positive charge due to the electron-withdrawing effect of the chlorine atom. This makes them more susceptible to attack by an electrophile.

The diagram below shows the expected product distribution of the electrophilic aromatic substitution reaction between chlorobenzene and an electrophile such as nitronium ion (NO2+). The nitronium ion is an electrophile that is commonly used in the nitration of benzene derivatives.

The nitration reaction can occur at the ortho or para positions due to the ortho and para directing effect of the chlorine atom. The meta position is less favored because the chlorine atom withdraws electron density from the meta position, creating a partial negative charge that repels the incoming electrophile.

The diagram below shows the expected product distribution of the nitration reaction between chlorobenzene and nitronium ion:

NO2+ | Cl | C6H4Cl --> C6H3ClNO2 + C6H4ClNO2 | ortho product para product

The ortho and para products are both formed in significant amounts due to the ortho and para directing effect of the chlorine atom. This makes chlorobenzene a useful starting material for the synthesis of ortho- and para-substituted benzene derivatives.