NEET Chemistry — Amines Complete Chapter Guide

Chapter Overview & Weightage

Amines is the nitrogen chemistry chapter of Organic Chemistry. Basicity, named reactions (Gabriel, Hofmann, diazotization), and classification are the core topics. NEET tests both conceptual understanding and factual recall.

Amines carries 3-4% weightage in NEET with 1-2 questions. Basicity order and diazonium salt reactions are the most tested topics.

Year	NEET Q Count	Key Topics Tested
2025	2	Basicity order, Hinsberg test
2024	1	Gabriel synthesis
2023	2	Diazonium reactions, Hofmann degradation
2022	2	Basicity, carbylamine test
2021	1	Classification, Sandmeyer reaction

graph TD
    A[Amines] --> B[Classification]
    A --> C[Basicity]
    A --> D[Preparation]
    A --> E[Reactions]
    B --> F[Primary, Secondary, Tertiary]
    C --> G[Aliphatic > Aromatic]
    C --> H[Effect of Substituents]
    D --> I[Gabriel Synthesis]
    D --> J[Hofmann Bromamide]
    E --> K[Diazotization]
    E --> L[Sandmeyer Reaction]
    E --> M[Coupling Reaction: Azo dyes]

Key Concepts You Must Know

Tier 1 (Always asked)

Basicity order: aliphatic amines > NH $_3$ > aromatic amines
In aqueous solution: R $_2$ NH > RNH $_2$ > R $_3$ N (solvation effect)
Diazonium salt reactions: Sandmeyer, Gattermann
Gabriel synthesis: gives primary amines only
Carbylamine test: positive for primary amines only

Tier 2 (Frequently asked)

Hofmann bromamide degradation (amide to amine, one carbon less)
Hinsberg test: distinguishes 1 degree, 2 degree, 3 degree amines
Coupling reaction (diazonium + phenol/amine gives azo dye)
Effect of EWG/EDG on basicity of aniline

Tier 3 (Occasional)

Mannich reaction
Mustard gas from amines
Quaternary ammonium salts

Important Formulas

In gas phase: R $_3$ N > R $_2$ NH > RNH $_2$ > NH $_3$ (pure inductive effect)

In aqueous solution: R $_2$ NH > RNH $_2$ > R $_3$ N > NH $_3$ (solvation plays a role for tertiary)

For aromatic amines: electron-donating groups on ring increase basicity, electron-withdrawing groups decrease it.

p-CH $_3$ -C $_6$ H $_4$ -NH $_2$ is more basic than aniline (CH $_3$ is EDG).

p-NO $_2$ -C $_6$ H $_4$ -NH $_2$ is less basic than aniline (NO $_2$ is EWG).

Gabriel: Phthalimide + KOH + RX, then hydrolysis gives RNH $_2$ (primary only)

Hofmann bromamide: RCONH $_2$ + Br $_2$ /NaOH gives RNH $_2$ (one carbon less)

Diazotization: ArNH $_2$ + NaNO $_2$ + HCl (0-5 degree C) gives ArN $_2^+$ Cl $^-$

Sandmeyer: ArN $_2^+$ + CuX/HX gives ArX (X = Cl, Br, CN)

Coupling: ArN $_2^+$ + PhOH/PhNH $_2$ gives Ar-N=N-Ar’ (azo dye, at 0-5 degree C)

Test	Reagent	Positive for	Result
Carbylamine	CHCl $_3$ + NaOH	1 degree amines	Foul-smelling isocyanide
Hinsberg	PhSO $_2$ Cl	Distinguishes 1/2/3 degree	Different solubility
Nitrous acid	NaNO $_2$ + HCl	All classes	Different products

Gabriel synthesis gives ONLY primary amines because the mechanism involves phthalimide (which has only one N-H equivalent after deprotonation). If NEET asks “which method gives only primary amines” — Gabriel is the answer.

Solved Previous Year Questions

PYQ 1 — NEET 2023

Problem: Arrange in decreasing order of basicity: aniline, p-nitroaniline, p-methoxyaniline, p-toluidine.

Solution:

Basicity depends on electron density on nitrogen:

p-OCH $_3$ (EDG by resonance) increases basicity strongly
p-CH $_3$ (EDG by hyperconjugation) increases basicity mildly
p-NO $_2$ (EWG by resonance) decreases basicity strongly

Order: p-methoxyaniline > p-toluidine > aniline > p-nitroaniline

PYQ 2 — NEET 2022

Problem: Carbylamine reaction is given by:

Solution:

Carbylamine (isocyanide) test is positive for primary amines only (both aliphatic and aromatic):

R\text{-}NH_2 + CHCl_3 + 3KOH \to R\text{-}NC + 3KCl + 3H_2O

The foul smell of isocyanide (R-NC) confirms a primary amine.

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	40%	Basicity order, test identification
Medium	45%	Named reactions, diazonium products
Hard	15%	Multi-step synthesis via diazonium

Expert Strategy

Week 1: Basicity order — gas phase vs aqueous. Understand WHY tertiary amines are not the most basic in water (poor solvation of the conjugate acid).

Week 2: Named reactions and preparation methods. Diazonium salt chemistry is a reaction powerhouse — from one intermediate, you can make ArOH, ArX, ArCN, ArH, and azo dyes.

Week 3: Distinction tests and revision. Carbylamine for 1 degree, Hinsberg for distinguishing all three, nitrous acid for different products.

Common Traps

Trap 1 — Basicity in water is not the same as in gas phase. In gas phase, 3 degree > 2 degree > 1 degree. In water, 2 degree > 1 degree > 3 degree (for aliphatic). The difference is solvation — tertiary ammonium ions are poorly solvated.

Trap 2 — Diazonium salts are unstable above 5 degrees C. All diazonium reactions must be done at 0-5 degrees C. If the temperature rises, the diazonium salt decomposes to phenol. A question mentioning “room temperature” with ArN $_2^+$ often leads to phenol as the product.

Trap 3 — Gabriel synthesis does not work for aromatic amines. Aryl halides do not undergo SN2 with potassium phthalimide. Gabriel works only for aliphatic primary amines.