The Question is from neet-chemistry haloalkanes-haloarenes , and it was created by the author P SRAVAN KUMAR

Question

Arrange the following aryl halides in decreasing order of reactivity towards electrophilic aromatic substitution:
I. Bromobenzene
II. 4-Bromonitrobenzene
III. 2,4-Dibromobenzene
IV. 4-Bromoaniline

P SRAVAN KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Electrophilic Aromatic Substitution and activating/deactivating groups
 **Related Topics**: Resonance effects, inductive effects, Hammett constants
 **Prerequisites**: Understanding of electrophilic aromatic substitution mechanism and the effects of substituents on the reactivity of the benzene ring.
## SOLUTION PATHWAY
**Given Information**:
  Four aryl halides: Bromobenzene, 4-Bromonitrobenzene, 2,4-Dibromobenzene, 4-Bromoaniline.
  The question asks to arrange them in decreasing order of reactivity towards electrophilic aromatic substitution.
**Method & Steps**:
 1. Identify the substituents on the benzene ring and their effects on reactivity.
  Reasoning: Electron-donating groups (EDG) activate the ring towards electrophilic aromatic substitution, while electron-withdrawing groups (EWG) deactivate the ring.
  Substituents affect reactivity through resonance and inductive effects.  Halides are weakly activating via resonance but deactivating via induction.
 2. Analyze the effect of each substituent.
  Working:
  I. Bromobenzene ($C_6H_5Br$): Br is a weakly activating group through resonance (although it's a deactivating group via induction, the resonance effect is more significant here).
  II. 4-Bromonitrobenzene ($C_6H_4BrNO_2$):  NO2 is a strongly deactivating group (EWG) via both resonance and induction.  It significantly reduces the reactivity.
  III. 2,4-Dibromobenzene ($C_6H_4Br_2$): Two Br atoms are present.  The combined effect is still less reactive than bromobenzene alone.
  IV. 4-Bromoaniline ($C_6H_4BrNH_2$): NH2 is a strongly activating group (EDG) via both resonance and induction. It significantly increases the reactivity.
 3. Arrange the compounds in decreasing order of reactivity.
  Result: The order of reactivity is IV > I > III > II.  4-Bromoaniline is the most reactive due to the strongly activating -NH2 group, followed by Bromobenzene (weakly activated by Br), then 2,4-Dibromobenzene (two Br atoms, less reactive than bromobenzene), and finally 4-Bromonitrobenzene (strongly deactivated by -NO2).
  Verification: The order aligns with the understanding of activating and deactivating groups in electrophilic aromatic substitution.
 ## OPTION ANALYSIS
A :x: Incorrect order of reactivity.
B ✓: Correct order of reactivity: IV > I > III > II
C :x: Incorrect order of reactivity.
D :x: Incorrect order of reactivity.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Ignoring the relative strengths of activating and deactivating groups: Students may not consider the strength of the inductive and resonance effects of different substituents.
  How to avoid: Carefully analyze the resonance and inductive effects of each substituent and compare their relative strengths.
  2.Overlooking the combined effect of multiple substituents: If multiple substituents are present, their combined effect must be considered.
  How to avoid:  Consider the effects of each substituent individually and then determine their overall effect on the reactivity of the ring.
 **Quick Tips**:
  1.Memorize the common activating and deactivating groups and their relative strengths.
  2.Draw resonance structures to visualize the electron distribution in the aromatic ring.

P SRAVAN KUMAR · Answer

I > II > III > IV

P SRAVAN KUMAR · Answer

The correct Option is "IV > I > III > II"

P SRAVAN KUMAR · Answer

II > III > I > IV

P SRAVAN KUMAR · Answer

IV > III > I > II

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