Before You Begin

Question #45044

Difficulty: 8/10 | 🟢 Free

The Question

Aniline is subjected to direct nitration using a standard nitrating mixture (conc. $\ce{HNO3}$ and conc. $\ce{H2SO4}$ ) at $288\text{ K}$ . Surprisingly, alongside the expected ortho and para derivatives, a significant amount of the meta-isomer is formed. Identify the approximate percentage yield of the meta-isomer, the hybridization of the nitrogen atom in the reactive intermediate responsible for this meta-direction, and the dominant electronic effect exerted by this modified substituent.

Options

A.
47%, $sp^3$ , $-I$ effect
B.
51%, $sp^2$ , $+M$ effect
C.
47%, $sp^2$ , $-M$ effect
D.
2%, $sp^3$ , $+I$ effect

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Hybridization and Geometry|Aniline Resonance Pitfalls|Azo Coupling Regioselectivity

Why This Question Is Tricky

Common Mistakes

This question tests the 'Chemical Exception' of aniline's reactivity in strongly acidic media.

Students often blindly apply the rule that $-\ce{NH2}$ is a strong ortho/para directing activator due to its $+M$ effect.

The trap lies in failing to account for the acid-base thermodynamics that precede the Electrophilic Aromatic Substitution (EAS).

In the nitrating mixture, aniline is protonated to the anilinium ion.

This protonation fundamentally alters the nitrogen's geometry from an $sp^2$ -like state (capable of resonance overlap) to a strictly $sp^3$ tetrahedral state.

The sequestration of the lone pair nullifies the $+M$ effect, leaving only a strong $-I$ effect, which converts the substituent into a meta-directing deactivator, yielding an anomalously high 47% of the meta-isomer.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Hybridization and Geometry
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free