Q.92 Chemistry · Section B ⭐ 360° Option Elimination Active

Vault ↗

NEET 2024 Chemistry Question 92 Solution

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

Question

For the given reaction: C₆H₁₁−CH=CH−C₆H₁₁ (C₆H₁₁ = cyclohexyl) → (KMnO₄/H⁺) 'P' (major product). 'P' is

✓

Verified Against NTA Final Answer Key

Option (4) : Cyclohexanecarboxylic acid (Cyclohexyl-COOH)

📚 Aldehydes, Ketones and Carboxylic Acids Easy

📋 Given Parameters & Problem Setup

Starting reactant 1,2-dicyclohexylethene (Cyclohexyl-CH=CH-Cyclohexyl)

Reagent Hot acidic potassium permanganate (KMnO4 / H⁺)

⚡

The 30-Second Exam Hall Shortcut: ⚡ Alkene Oxidative Cleavage Rule

⏱️ Save ~35 seconds

Hot acidic KMnO4 completely cleaves C=C! =CH-R groups oxidize to carboxylic acid (-COOH)! Symmetrical Cyclohexyl-CH=CH-Cyclohexyl cleaves into 2 molecules of Cyclohexanecarboxylic acid!

1 Identify the alkene: Cyclohexyl-CH=CH-Cyclohexyl (symmetrical 1,2-disubstituted alkene).

2 Recall vigorous oxidation with hot acidic KMnO4 / H⁺:

3 - =CH2 oxidizes to CO2 + H2O.

4 - =CH-R oxidizes to carboxylic acid (R-COOH).

5 - =CR2 oxidizes to ketone (R-CO-R).

6 Here, each side of the double bond is a -CH(Cyclohexyl) group.

7 Cleavage of the double bond oxidizes both halves to cyclohexanecarboxylic acid (Cyclohexyl-COOH).

8 Match Option (4) in 5 seconds!

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Aldehydes, Ketones and Carboxylic Acids (Preparation of carboxylic acids by oxidation of alkenes using acidic potassium permanganate).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Nature of the Oxidizing Reagent

Acidic potassium permanganate (KMnO4 / H⁺) is a potent, vigorous oxidizing agent that causes oxidative cleavage of carbon-carbon double bonds. Unlike cold dilute alkaline KMnO4 (Baeyer’s reagent) which performs syn-dihydroxylation, hot acidic KMnO4 completely ruptures both the σ and π components of the alkene:

R{-}\text{CH}=\text{CH}{-}R \xrightarrow{\text{KMnO}_4 / \text{H}^\oplus, \; \Delta} 2\; R{-}\text{COOH}

Step 2

Oxidative Fate of Alkene Carbon Atoms

The products of oxidative cleavage depend on the substitution of the alkene carbons: 1. Disubstituted carbon (=CR2) yields a ketone (R2C=O). 2. Monosubstituted carbon (=CHR) is oxidized past the aldehyde stage directly to a carboxylic acid (R-COOH). 3. Terminal methylene (=CH2) is oxidized to formic acid, which is rapidly oxidized further to CO2 and H2O.

=\text{CH}{-}\text{R} \xrightarrow{[\text{O}]} R{-}\text{CHO} \xrightarrow{\text{fast } [\text{O}]} R{-}\text{COOH}

Step 3

Application to 1,2-Dicyclohexylethene

The substrate possesses two identical monosubstituted alkene carbons bonded to cyclohexyl rings. Cleavage of the central double bond produces two equivalents of cyclohexanecarboxylic acid:

\text{Cyclohexyl}{-}\text{CH}=\text{CH}{-}\text{Cyclohexyl} \xrightarrow{\text{KMnO}_4 / \text{H}^\oplus} 2\;\text{Cyclohexyl}{-}\text{COOH} \quad (\text{Product P})

⭐

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)

✗ Incorrect

Verdict & Scientific Reason:

Formed with cold alkaline KMnO4 (Baeyer’s reagent), not hot acidic KMnO4.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing hot acidic KMnO4 with Baeyer’s dihydroxylation.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Mild oxidation intermediate; under acidic KMnO4, the C-C bond cleaves completely.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming C-C bond remains intact.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Formed by reductive ozonolysis (O3 / Zn-H2O); KMnO4 over-oxidizes aldehydes to carboxylic acids.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing KMnO4 oxidation with reductive ozonolysis.

4 (4)

✓ 100% Correct

Verdict & Scientific Reason:

Exact product of vigorous permanganate cleavage of a 1,2-disubstituted alkene.

💡

Why this is airtight: None.

⚠️

NTA Trap Alert: Confusing Acidic KMnO4 with Ozonolysis or Baeyer’s Reagent

O3/Zn gives aldehyde (Option 3); cold KMnO4 gives diol (Option 1); hot acidic KMnO4 gives carboxylic acid (Option 4)!

🛡️ How to avoid the -1 mark: Hot acidic KMnO4 = Total double bond cleavage all the way to carboxylic acid.

📖

Core NEET Syllabus Standard

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

Core Scientific Principle Tested:

"Alkenes with =CH-R groups undergo oxidative cleavage by acidic potassium permanganate to yield carboxylic acids R-COOH."

Syllabus Focus: Preparation of Carboxylic Acids: Oxidative Cleavage of Alkenes

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Acidic permanganate cuts the bond clean: =CH-R turns to acid unseen!

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 200-minute timed NTA simulator.

Launch NEET 2024 CBT Test →

← Previous (Q.91) All Chemistry Questions Grid Next (Q.93) →

Spotted a mistake in this solution? Report an error ([email protected])

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2024 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

NEET 2024 Chemistry Question 92 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Alkene Oxidative Cleavage Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Nature of the Oxidizing Reagent

Oxidative Fate of Alkene Carbon Atoms

Application to 1,2-Dicyclohexylethene

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Acidic KMnO4 with Ozonolysis or Baeyer’s Reagent

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Aldehydes, Ketones and Carboxylic Acids

Friedel-Crafts Acylation Followed by Haloform Cleavage

Regiochemical Selectivity in Aldol Dehydration Products

Étard Reaction & Rosenmund Reduction of Benzaldehyde

Decreasing Order of Acidity of Aliphatic Carboxylic Acids (+I Inductive Effect)

Solve 4 NEET Questions a Day — One per Subject