The most deactivating group for electrophillic substitution reaction in benzene ring? A) -NH2 B) -NO2 C) -OCH3 D) -CHO also pls explain.?

Question

Answer

The most deactivating group is -CHO bcoz

1)It has very high -M/-H

2)It decreases the electron density on benzene ring for ESR.

Answer

Deactivating groups decrease the electron density on benzene ring making further substitution difficult so these groups direct incoming group(electrophile)  to meta position( electron rich position)  hence also called as meta directing groups.Here -NH2 and -OCH3 are activating groups/Ortho and para directing groups.-NO2 and -CHO are deactivating groups among these two NO2 is most deactivating due to its strong -I effect.

Answer

Introduction:
Electrophilic substitution reactions are organic reactions in which an electrophile reacts with a nucleophile, resulting in the substitution of one atom or group on a molecule with another. In benzene rings, these reactions are commonly observed due to the high electron density and stability of the aromatic system. However, certain substituents can deactivate the benzene ring towards electrophilic substitution reactions by withdrawing electron density from the ring.

Explanation:
The deactivating effect of substituents on benzene rings can be attributed to their ability to withdraw electron density through inductive and resonance effects. The most deactivating group for electrophilic substitution reaction in a benzene ring is -NO2 (nitro group).

Inductive Effect:
The inductive effect is the withdrawal or donation of electron density through sigma bonds. Substituents with electronegative atoms, such as oxygen or nitrogen, can withdraw electron density from the benzene ring through the inductive effect. This decreases the electron density on the ring, making it less reactive towards electrophilic substitution reactions.

Resonance Effect:
The resonance effect is the withdrawal or donation of electron density through pi bonds. Substituents with pi bonds, such as carbonyl groups, can withdraw electron density from the benzene ring through resonance. This occurs when the substituent can delocalize its pi electrons into the benzene ring, resulting in a decrease in electron density on the ring.

Comparing the Substituents:
Let's compare the substituents -NH2, -NO2, -OCH3, and -CHO to determine the most deactivating group for electrophilic substitution reactions:

- -NH2 (amino group) has a lone pair of electrons that can donate electron density through resonance, making it a weak activator towards electrophilic substitution reactions. It has a moderate electron-donating effect.
- -NO2 (nitro group) has both inductive and resonance effects, withdrawing electron density from the benzene ring. It is a strong deactivator and greatly reduces the reactivity of the ring towards electrophilic substitution reactions.
- -OCH3 (methoxy group) has a lone pair of electrons that can donate electron density through resonance, making it a weak activator towards electrophilic substitution reactions. However, the electron-donating effect is weaker than -NH2.
- -CHO (aldehyde group) has a carbonyl group that can withdraw electron density from the benzene ring through resonance. It is a moderate deactivator and reduces the reactivity of the ring towards electrophilic substitution reactions.

Conclusion:
Among the given substituents, the most deactivating group for electrophilic substitution reactions in a benzene ring is -NO2 (nitro group). It exhibits both inductive and resonance effects, effectively reducing the electron density on the ring and making it less reactive towards electrophilic substitution reactions.

Similar NEET Doubts

Meta-directing group towards electrophilic substitution reaction in benzene is

An example of electrophilic substitution reaction is

Dows reaction involves

The bromination of benzene in presence of FeBr is an example of

Dow's reaction involves

Top Courses for NEETView all

Biology Class 11

Daily Test for NEET Preparation

NEET Mock Test Series 2025

Topic-wise MCQ Tests for NEET

Physics Class 11

Top Courses for NEET

Top Courses for NEET

Suggested Free Tests

Related Content

About NEET

NEET Preparation Material

How to Prepare for NEET Exam?

NCERT Based Study Material

NEET Mock Tests

Other Popular Exams

Company