Chlorine's Role in Electrophilic Aromatic Substitution

Chlorine acts as an ortho and para director in electrophilic aromatic substitution (EAS) reactions despite being an electron-withdrawing group. This behaviour is explained by a combination of inductive and resonance effects.

Analyzing the Effects of Chlorine

• Statement (A): Chlorine withdraws electrons through inductive effect. This statement is correct. Due to chlorine's high electronegativity, it pulls electron density away from the benzene ring through the sigma bond (inductive effect, denoted as -I).
• Statement (B): Chlorine destabilises the intermediate carbocation formed during electrophilic substitution. This statement is correct. The inductive withdrawal (-I effect) reduces the overall electron density in the ring. This makes the intermediate carbocation (sigma complex) formed during EAS less stable compared to that in benzene, leading to the deactivation of the ring towards EAS.
• Statement (C): Chlorine accepts electrons through resonance. This statement is incorrect.
• Statement (D): Chlorine releases electrons through resonance. This statement is correct. Chlorine has lone pairs of electrons that can be donated into the pi system of the benzene ring through resonance (mesomeric effect, denoted as +M). This electron donation is most significant at the ortho and para positions.

Explaining Ortho/Para Direction

While the inductive effect (-I) of chlorine withdraws electron density and destabilizes the intermediate carbocation (making it a deactivator), the resonance effect (+M) donates electron density, particularly to the ortho and para positions. This resonance donation preferentially stabilizes the carbocation intermediate formed when the electrophile attacks the ortho or para positions compared to the meta position. Consequently, the resonance effect dictates the regioselectivity, making chlorine an ortho and para director.

Therefore, the behaviour of chlorine is attributed to statements (A), (B), and (D).