The Question is from neet-chemistry haloalkanes-haloarenes , and it was created by the author Mr. S M HUSSAIN

Question

Predict the major product of the reaction of 1-bromo-4-nitrobenzene with potassium tert-butoxide in tert-butanol.

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
	**Primary Concept**: Nucleophilic Aromatic Substitution (specifically, elimination-addition)
	**Related Topics**: Aromaticity, Leaving groups, Strong bases, Steric hindrance
	**Prerequisites**: Understanding of resonance structures, SNAr mechanism
## SOLUTION PATHWAY
**Given Information**:
	1-bromo-4-nitrobenzene reacts with potassium tert-butoxide.
	Solvent: tert-butanol
**Method & Steps**:
	1. **Identify the reactants**: 1-bromo-4-nitrobenzene is an aryl halide, and potassium tert-butoxide is a strong, bulky base.
		Reasoning:  A strong base suggests elimination or substitution. The bulky nature of tert-butoxide hinders direct substitution (SN2 is not possible on an sp2 carbon). 
	2. **Mechanism - Elimination-Addition (benzyne mechanism)**:
		Working:
			a.  The strong base, tert-butoxide, abstracts a proton *ortho* to the bromine atom.
			b.  This leads to the formation of a carbanion, which eliminates bromide ion to form a highly reactive intermediate called *benzyne*.
			c.  The tert-butoxide anion then attacks the benzyne intermediate, followed by protonation to give the product.
		Key Point: The nitro group is a strong electron-withdrawing group and stabilizes the negative charge formed during the elimination step, favoring the benzyne mechanism.  Also, the bulky tert-butoxide preferentially attacks the less hindered carbon of the benzyne intermediate.
	3. **Product Formation**:
		Result: The major product is 4-tert-butoxy-1-nitrobenzene.
		Verification: The benzyne intermediate is symmetrical in this case (due to the para positioning of the nitro group relative to bromine).  Attack at either end of the triple bond by tert-butoxide leads to the same product.  
## OPTION ANALYSIS
[A] ✓: 4-tert-butoxy-1-nitrobenzene: This is the correct product formed via the benzyne mechanism.
[B] :x: 2-tert-butoxy-1-nitrobenzene: While this product could theoretically form via the benzyne mechanism if the bromine and nitro group were ortho to each other, it's not formed in this case.
[C] :x: 1-bromo-4-tert-butoxybenzene: This would imply a direct substitution of bromine by tert-butoxide, which is unlikely due to the bulky nature of the base and the activating effect of the nitro group for the benzyne mechanism.
[D] :x: No reaction: The reaction conditions favor the benzyne mechanism, and a reaction will occur.
## LEARNING AIDS
	**Common Mistakes**:
		1. Assuming SNAr (addition-elimination) mechanism: This is less likely with a strong, bulky base like tert-butoxide.
			How to avoid: Recognize that strong, bulky bases favor elimination reactions, leading to the benzyne mechanism.
		2. Ignoring the effect of the nitro group: The nitro group stabilizes the negative charge formed during elimination, facilitating the benzyne mechanism.
			How to avoid: Consider the electronic effects of substituents on the aromatic ring.
	**Quick Tips**:
		1. Strong bases and aryl halides often lead to the benzyne mechanism.
		2. Electron-withdrawing groups ortho or para to the leaving group favor the benzyne mechanism.

Mr. S M HUSSAIN · Answer

The correct Option is "4-tert-butoxy-1-nitrobenzene"

Mr. S M HUSSAIN · Answer

2-tert-butoxy-1-nitrobenzene

Mr. S M HUSSAIN · Answer

1-bromo-4-tert-butoxybenzene

Mr. S M HUSSAIN · Answer

No reaction

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