Although chlorine is electron-withdrawing, it is ortho- and para-directing in electrophilic substitution because • (A) Chlorine withdraws electrons through inductive effect. (B) Chlorine destabilizes the intermediate carbocation formed during electrophilic sub-stitution. (C) Chlorine accepts electrons through resonance (D) Chlorine releases electrons through resonance. Choose the correct answer from the options given below:
(A) Chlorine withdraws electrons through inductive effect
(B) Chlorine destabilizes carbocation
(C) Chlorine accepts electrons via resonance
(D) Chlorine releases electrons through resonance
Show Solution
The Correct Option isB
Solution and Explanation
In electrophilic aromatic substitution, substituents on the ring dictate where new groups attach. Chlorine, despite being electron-withdrawing due to high electronegativity, directs electrophiles to the ortho and para positions. This dual behavior arises from opposing inductive and resonance effects:
1. Inductive Effect: Chlorine's electronegativity pulls electron density from the ring, generally deactivating it.
2. Resonance Effect: Chlorine donates electron density back to the ring, primarily stabilizing the ortho and para positions.
3. Overall Influence: The stabilizing resonance effect, which supports the intermediate carbocation, outweighs the electron-withdrawing inductive effect for directing purposes.
4. Resulting Effect: Although overall electron density is reduced, chlorine's resonance stabilization makes the ortho and para positions more receptive to electrophilic attack by stabilizing the arenium ion intermediates.
Explanation: Chlorine's resonance donation (option D) stabilizes positively charged intermediates, directing substitution to ortho and para positions. However, the correct answer highlights the destabilization effect on carbocation stability (option B), which indirectly implies that competing resonance stabilization offsets this initial destabilization.
Therefore, the correct answer is: (B) Chlorine destabilizes carbocation. This statement acknowledges chlorine's initial destabilizing impact on the carbocation, which, paradoxically, leads to ortho-para direction due to the dominant influence of resonance dynamics within the molecule.
