Before You Begin

Question #45039

Difficulty: 8/10 | 🟢 Free

The Question

Consider the electrophilic aromatic nitration of chlorobenzene using a mixture of concentrated $\ce{HNO3}$ and $\ce{H2SO4}$ at 298 K. The regioselectivity of the reaction is governed by the stability of the intermediate arenium ion (Wheland intermediate). In the most stable resonance contributor of the sigma complex formed during para-attack, the chlorine atom participates in back-bonding (+M effect). Determine the formal charge (FC) and the oxidation state (OS) of the chlorine atom in this specific resonance contributor, and identify the overall kinetic rate of nitration ( $k_{\ce{PhCl}}$ ) relative to benzene ( $k_{\ce{PhH}}$ ).

Options

A.
+1, -1, $k_{\ce{PhCl}} < k_{\ce{PhH}}$
B.
+1, +1, $k_{\ce{PhCl}} < k_{\ce{PhH}}$
C.
-1, +1, $k_{\ce{PhCl}} > k_{\ce{PhH}}$
D.
+1, -1, $k_{\ce{PhCl}} > k_{\ce{PhH}}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Fractional Oxidation State Misconception|Aryl Halide Resonance|Electrophilic Substitution Activation/Deactivation

Why This Question Is Tricky

Common Mistakes

This problem targets the 'Aryl Halide Resonance' trap and the misconception of 'Fractional Oxidation States'.

Students frequently conflate Formal Charge with Oxidation State.

When chlorine donates a lone pair to stabilize the arenium ion, it acquires a +1 formal charge, leading students to incorrectly assume its oxidation state changes to +1.

However, because chlorine is more electronegative than carbon, its oxidation state remains -1.

Furthermore, it tests the classic EAS exception: halogens are ortho/para directing due to transition state stabilization (+M), but overall deactivating because the inductive electron withdrawal (-I) dominates the ground state energy, making the reaction slower than benzene.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Redox Reactions - Class 11 Part 2
Concept	Fractional Oxidation State Misconception
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free