Q.102 Chemistry ⭐ 360° Option Elimination Active

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NEET 2020 Chemistry Question 102 Solution

Topic: Amines · Official NTA Booklet Code E1

Question

Which of the following amine will give the carbylamine test?

✓

Verified Against NTA Final Answer Key

Option (1) : Aniline (C6H5-NH2)

📚 Amines Easy

📋 Given Parameters & Problem Setup

Diagnostic Chemical Test Carbylamine test (Isocyanide test: CHCl3 + alc. KOH / Δ)

Criterion Must be a primary (1°) amine (aliphatic or aromatic)

Question Objective Identify which amine gives the carbylamine test

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Carbylamine Test = ONLY Primary (1°) Amines! Aniline (C6H5-NH2) is 1°!"

⏱️ 20 seconds

Carbylamine reaction is given exclusively by PRIMARY amines ( $R-NH_2$ or $Ar-NH_2$ ) when heated with chloroform and alcoholic KOH, producing extremely foul-smelling isocyanides ( $R-NC$ ). Secondary and tertiary amines DO NOT show this test. Among the choices, Aniline ( $C_6H_5-NH_2$ ) is a primary amine! Mark Aniline (Option 1) in 5 seconds.

1 Principle: Only primary (1°) amines undergo carbylamine reaction.

2 Reaction: R-NH2 + CHCl3 + 3KOH (alc.) -> R-NC (foul smell) + 3KCl + 3H2O.

3 Analyze options: - Option (1): Aniline (C6H5-NH2) -> Primary amine (1°). - Option (2): N-Methylaniline (C6H5-NH-CH3) -> Secondary amine (2°). - Option (3): N,N-Dimethylaniline (C6H5-N(CH3)2) -> Tertiary amine (3°). - Option (4): Secondary aliphatic amine.

4 Thus, only Aniline gives the carbylamine test.

5 Select Option (1).

🛡️

Why You Can 100% Trust This Shortcut: NCERT Chemistry · Amines (Chemical Reactions: Carbylamine Reaction / Isocyanide Test)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Understand the Carbylamine Reaction

When aliphatic or aromatic primary amines are heated with chloroform ( $\text{CHCl}_3$ ) and alcoholic potassium hydroxide ( $\text{KOH}$ ), they form carbylamines or isocyanides ( $\text{R-NC}$ ), which possess an intensely foul, offensive smell: $\text{R-NH}_2 + \text{CHCl}_3 + 3\text{KOH} \xrightarrow{\Delta} \text{R-NC} + 3\text{KCl} + 3\text{H}_2\text{O}$

Step 2

Specificity for Primary Amines

Secondary ( $2^\circ$ ) and tertiary ( $3^\circ$ ) amines do not give this reaction because they lack the required two hydrogen atoms on the nitrogen atom to form the isocyanide ( $-\text{N}\equiv\text{C}$ ) functional group.

Step 3

Classify the Given Amines

- Option (1): Aniline ( $\text{C}_6\text{H}_5-\text{NH}_2$ ) has an $\text{-NH}_2$ group attached to a phenyl ring, making it a primary ( $1^\circ$ ) aromatic amine. - Option (2): $N$ -methylaniline ( $\text{C}_6\text{H}_5-\text{NH}-\text{CH}_3$ ) is a secondary ( $2^\circ$ ) amine. - Option (3): $N,N$ -dimethylaniline ( $\text{C}_6\text{H}_5-\text{N}(\text{CH}_3)_2$ ) is a tertiary ( $3^\circ$ ) amine. - Option (4): Diethylamine ( $(\text{C}_2\text{H}_5)_2\text{NH}$ ) is a secondary ( $2^\circ$ ) amine.

Step 4

Conclude Aniline

Aniline is the only primary amine among the choices, and thus it alone gives the carbylamine test.

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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 A

✓ 100% Correct

Verdict & Scientific Reason:

Factually exact; aniline is a primary amine ( $1^\circ$ ) and reacts to produce foul-smelling phenyl isocyanide ( $C_6H_5-NC$ ).

💡

Why this is airtight: None; textbook distinction between 1°, 2°, and 3° amines.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; $N$ -methylaniline is a secondary amine ( $2^\circ$ ), which does not respond to the carbylamine test.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming all aromatic amines give carbylamine test regardless of degree.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; $N,N$ -dimethylaniline is a tertiary amine ( $3^\circ$ ) and does not undergo isocyanide formation.

⚠️

Student Fallacy (Why candidates pick this trap): Failing to check degree of nitrogen substitution.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect; secondary aliphatic amines do not give the carbylamine test.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing Hinsberg test reactivity with carbylamine test.

⚠️

NTA Trap Alert: Aromatic vs Aliphatic in Carbylamine Test

Carbylamine test is given by BOTH ALIPHATIC AND AROMATIC primary amines! The only requirement is that it must be PRIMARY ( $-\text{NH}_2$ ).

🛡️ How to avoid the -1 mark: Look for the

-NH_2

group! Only

1^\circ

amine gives carbylamine test!

📖

Core NEET Syllabus Standard

Chemistry · Amines Standard Benchmark

Core Scientific Principle Tested:

Syllabus Focus: Carbylamine Reaction: Exclusive Diagnostic Test for Primary Amines

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2020 Chemistry Question 102 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Carbylamine Test = ONLY Primary (1°) Amines! Aniline (C6H5-NH2) is 1°!"

Step-by-Step Rigorous Workflow & Mathematical Proof

Understand the Carbylamine Reaction

Specificity for Primary Amines

Classify the Given Amines

Conclude Aniline

360° Option Elimination Engine Key Feature

NTA Trap Alert: Aromatic vs Aliphatic in Carbylamine Test

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Amines

Preparation Methods of Primary Aromatic Amines (Aniline)

Decreasing Order of Basic Strength of Substituted Amines in Aqueous Medium

Limitations of Friedel-Crafts and Gabriel Phthalimide Syntheses with Aniline

Multistep Synthesis: Cyanation, Partial Hydrolysis, and Hoffmann Degradation

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