Q.71 Chemistry · Section A ⭐ 360° Option Elimination Active

NEET 2024 Chemistry Question 71 Solution

Topic: Aldehydes, Ketones and Carboxylic Acids · Official NTA Booklet Code T1

Question

Match List I (Reaction) with List II (Reagents/Condition). List I: A. Cyclohexylidenecyclohexane → 2 cyclohexanone; B. Benzene → benzophenone; C. Cyclohexanol → cyclohexanone; D. Ethylbenzene → potassium benzoate. List II: I. Benzoyl chloride / Anhyd. AlCl₃; II. CrO₃; III. KMnO₄/KOH, Δ; IV. (i) O₃ (ii) Zn-H₂O. Choose the correct answer from the options given below:

✓

Verified Against NTA Final Answer Key

Option (1) : A-IV, B-I, C-II, D-III

📚 Aldehydes, Ketones and Carboxylic Acids Easy

📋 Given Parameters & Problem Setup

Reaction A Bicyclohexylidene -> 2 Cyclohexanone

Reaction B Benzene -> Benzophenone

Reaction C Cyclohexanol -> Cyclohexanone

Reaction D Ethylbenzene -> Potassium benzoate

⚡

The 30-Second Exam Hall Shortcut: ⚡ Reagent Function Matching Hack

⏱️ Save ~40 seconds

Alkene cleavage -> Ozonolysis (IV); Benzene to ketone -> PhCOCl/AlCl3 (I); 2° alcohol to ketone -> CrO3 (II); Side-chain alkylbenzene to benzoate -> KMnO4/KOH, Δ (III)!

1 Bicyclohexylidene is cleaved across the C=C double bond into two ketone rings -> Reductive Ozonolysis: (i) O3, (ii) Zn-H2O (A-IV).

2 Benzene + Benzoyl chloride with anhydrous AlCl3 gives benzophenone via Friedel-Crafts acylation -> PhCOCl / Anhyd. AlCl3 (B-I).

3 Cyclohexanol (2° alcohol) is oxidized to cyclohexanone -> Chromic anhydride CrO3 (C-II).

4 Ethylbenzene heated with alkaline potassium permanganate oxidizes the benzylic carbon to potassium benzoate -> KMnO4 / KOH, Δ (D-III).

5 Match: A-IV, B-I, C-II, D-III -> Option (1) in 5 seconds!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Aldehydes, Ketones and Carboxylic Acids (Preparation of aldehydes and ketones by ozonolysis, acylation, oxidation of alcohols, and oxidation of alkylbenzenes).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Ozonolysis of Symmetrical Alkene (Reaction A)

Bicyclohexylidene is an alkene where two cyclohexyl rings are joined by an endocyclic/exocyclic double bond. Reductive ozonolysis cleaves the double bond with ozone followed by zinc dust reduction, yielding two equivalents of cyclohexanone:

\text{Alkene} \xrightarrow{\text{(i) } \text{O}_3, \; \text{(ii) } \text{Zn-H}_2\text{O}} 2\;\text{Cyclohexanone} \quad (\text{IV})

Step 2

Friedel-Crafts Acylation of Benzene (Reaction B)

Benzene reacts with benzoyl chloride (C6H5COCl) in the presence of anhydrous aluminum chloride (Lewis acid catalyst) to form diphenylmethanone (benzophenone):

\text{C}_6\text{H}_6 + \text{C}_6\text{H}_5\text{COCl} \xrightarrow{\text{Anhyd. AlCl}_3} \text{C}_6\text{H}_5{-}\text{CO}{-}\text{C}_6\text{H}_5 + \text{HCl} \quad (\text{I})

Step 3

Mild Oxidation of Secondary Alcohol (Reaction C)

Cyclohexanol is a secondary (2°) alcohol. Oxidation with chromium trioxide (CrO3 in aqueous acetone / Jones-type conditions) cleanly yields the corresponding cyclic ketone, cyclohexanone:

\text{Cyclohexanol} \xrightarrow{\text{CrO}_3} \text{Cyclohexanone} \quad (\text{II})

Step 4

Vigorous Side-Chain Oxidation of Alkylbenzene (Reaction D)

Regardless of the length of the alkyl side chain (provided it contains at least one benzylic hydrogen), vigorous oxidation with alkaline KMnO4 cleaves the side chain, converting it into the potassium salt of benzoic acid:

\text{C}_6\text{H}_5\text{CH}_2\text{CH}_3 \xrightarrow{\text{KMnO}_4 / \text{KOH}, \; \Delta} \text{C}_6\text{H}_5\text{COOK} \quad (\text{III})

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 (1)

✓ 100% Correct

Verdict & Scientific Reason:

Exact match with all canonical reagent-reaction pairings.

💡

Why this is airtight: None.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Mismatches ozonolysis with acylation.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing alkene cleavage with Friedel-Crafts.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Swaps reagents for reactions C and D.

⚠️

Student Fallacy (Why candidates pick this trap): Using KMnO4 for mild alcohol oxidation.

4 (4)

✗ Incorrect

Verdict & Scientific Reason:

Uses alkaline KMnO4 for alkene ozonolysis.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing ozonolysis with permanganate cleavage.

⚠️

NTA Trap Alert: Confusing Side-Chain Oxidation with Ring Oxidation

In ethylbenzene, KMnO4/KOH oxidizes ONLY the benzylic side chain to -COOK, leaving the aromatic benzene ring completely intact.

🛡️ How to avoid the -1 mark: Remember: Aromatic rings with benzylic hydrogens always oxidize to benzoic acid/benzoate under hot alkaline KMnO4.

📖

Core NEET Syllabus Standard

Chemistry Core Organic Chemistry · Aldehydes, Ketones and Carboxylic Acids Standard Benchmark

Core Scientific Principle Tested:

"Ozonolysis cleaves C=C into carbonyls; PhCOCl/AlCl3 acylates benzene; CrO3 oxidizes 2° alcohols to ketones; alkaline KMnO4 oxidizes alkylbenzenes to benzoates."

Syllabus Focus: Methods of Preparation of Carbonyl Compounds and Carboxylic Acids

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ozone splits the double bond in two; Benzoyl chloride gives ketone through and through!

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NEET 2024 Chemistry Question 71 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Reagent Function Matching Hack

Step-by-Step Rigorous Workflow & Mathematical Proof

Ozonolysis of Symmetrical Alkene (Reaction A)

Friedel-Crafts Acylation of Benzene (Reaction B)

Mild Oxidation of Secondary Alcohol (Reaction C)

Vigorous Side-Chain Oxidation of Alkylbenzene (Reaction D)

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Side-Chain Oxidation with Ring Oxidation

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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