Solveeit Logo
Login

Question

Question: In which of the following compound the electrophile attack on o- and p- positions :...

In which of the following compound the electrophile attack on o- and p- positions :

A

Nitrobenzene (C₆H₅NO₂)

B

Chlorobenzene (C₆H₅Cl)

C

Trichloromethylbenzene (C₆H₅CCl₃)

D

Benzoic acid (C₆H₅COOH)

Answer

Chlorobenzene (C₆H₅Cl)

Explanation

Solution

Electrophilic attack on ortho (o-) and para (p-) positions occurs when the substituent on the benzene ring is an activating group or a halogen. Activating groups are electron-donating and increase electron density at o- and p- positions. Halogens are deactivating but are o- and p- directing due to the dominance of their +M (mesomeric) effect over their -I (inductive) effect in terms of directing ability.

Let's analyze each option:

  1. Nitrobenzene (C₆H₅NO₂): The -NO₂ group is a strong electron-withdrawing group by both resonance (-M effect) and induction (-I effect). It deactivates the benzene ring and is a meta-director. Therefore, electrophiles attack the meta position.

  2. Chlorobenzene (C₆H₅Cl): The -Cl group is a halogen. Halogens are deactivating groups due to their strong electron-withdrawing inductive effect (-I). However, they possess lone pairs of electrons that can be donated to the benzene ring via resonance (+M effect). The +M effect, while weaker than the -I effect in terms of overall reactivity, is dominant in terms of directing ability. This makes halogens ortho-para directors. Therefore, electrophiles attack the ortho and para positions.

  3. Trichloromethylbenzene (C₆H₅CCl₃): The -CCl₃ group is an electron-withdrawing group mainly due to the strong inductive effect (-I) of the three chlorine atoms. It deactivates the benzene ring and is a meta-director. Therefore, electrophiles attack the meta position.

  4. Benzoic acid (C₆H₅COOH): The -COOH group is an electron-withdrawing group by both resonance (-M effect) and induction (-I effect). It deactivates the benzene ring and is a meta-director. Therefore, electrophiles attack the meta position.

Based on the analysis, only chlorobenzene (2) directs electrophiles to the ortho and para positions.