Class 12 Chemistry · NCERT Chapter 9 (Part 2)

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Amines Class 12 Chemistry Notes

Amines build everything from amino acids to dyes and medicines. This chapter covers classification and nomenclature, ammonolysis and Gabriel synthesis, Hofmann degradation, the basicity order, the carbylamine test, diazonium salts and their Sandmeyer and coupling reactions.

Class:12Subject:ChemistryCovers:Gabriel · Hofmann · DiazoniumExams:CBSE · CUET · NEET

6 Key Formulas2 Solved Examples40 Practice MCQs

DWritten byDeep Narayan

UpdatedOctober 2026

Key Concept Summary

Why are alkyl amines basic but aniline very weakly basic?

Alkyl groups donate electron density (+I effect) to the nitrogen, making the lone pair more available; small amines are also stabilised by solvation in water, so 2° > 1° > 3° in aqueous basicity. In aniline the lone pair is delocalised over the aromatic ring by resonance, and it sits on an sp² nitrogen — both make it far less available — so aniline is much weaker than ammonia.

Classification and Nomenclature of Amines

Definition

Amine

A derivative of ammonia in which one, two or three hydrogen atoms are replaced by alkyl or aryl groups: 1° (RNH₂), 2° (R₂NH), 3° (R₃N). Quaternary ammonium salts (R₄N⁺X⁻) have no hydrogen on nitrogen.

Aliphatic vs aromatic: the nitrogen's carbon decides (aniline has an aryl group directly on N).
Mixed classes: di- and tri-amines (ethylenediamine), haloamines, amino alcohols.
IUPAC: alkan-1-amine, N-methylalkan-1-amine for 2°/3°; aromatic systems keep aniline, N-methylaniline.
Common names: methylamine, dimethylamine, aniline, toluidine.

Count N–H

The class is set by the number of H atoms on nitrogen (primary = 2, secondary = 1, tertiary = 0), not by the carbon count. Ammonia → methylamine is a one-H swap.

MCQ Questions

(CH₃)₂NH is a: (A) primary (B) secondary (C) tertiary (D) quaternary amine

Which of the following is an aromatic amine?

Preparation of Amines

Ammonolysis: R–X + NH₃ → RNH₂ (+2°, 3°, quaternary) — control with excess NH₃.
Gabriel phthalimide: potassium phthalimide + RH → hydrolysis → pure 1° amine.
Reduction: nitro compounds (Zn/HCl or H₂–Ni for aliphatic; aniline from nitrobenzene with Sn/HCl), nitriles (LiAlH₄/H₂–Ni), amides (LiAlH₄).
Hofmann bromamide degradation: RCONH₂ + Br₂ + NaOH → RNH₂ (one carbon removed).
Reductive amination: R₂C=O + NH₃ + H₂/Ni → R₂CH–NH₂.

Nitrobenzene to aniline — the aromatic 1° amine

\ce C 6 H 5 N O 2 - > [S n / H C l or H 2/ N i] C 6 H 5 N H 2

Which gives pure 1°?

Gabriel (phthalimide) and Hofmann (bromamide) both give clean primary amines — mix-free. Ammonolysis gives a mixture and must push excess NH₃.

MCQ Questions

Gabriel phthalimide synthesis is preferred for:

The Hofmann bromamide reaction converts an amide into an amine that has:

Physical Properties and Basicity

Smell: low amines have fishy/ammoniacal odour.
Boiling point: 1° > 2° > 3° among isomers — more N–H = more H-bonding; all above hydrocarbons.
Solubility: small amines dissolve in water via N–H···O hydrogen bonds; solubility drops with size.
Basicity arises from the nitrogen lone pair; any group that stabilises the alkyl ammonium ion or frees the lone pair raises it.

Definition

Order of basicity

Aqueous: 2° > 1° > 3° > NH₃ (steric + solvation). Gas phase: 3° > 2° > 1° > NH₃ (pure +I). Aromatic amines are much weaker than NH₃ (lone pair delocalised into ring; sp² nitrogen).

Substituent effects on aniline

Electron-donating groups (CH₃, OCH₃) raise aniline's basicity; electron-withdrawing (−NO₂, −X, −COOH) lower it. p‑nitroaniline < aniline < p‑toluidine — a classic MCQ.

MCQ Questions

In aqueous solution, the basicity order of methyl amines is:

Aniline is a weaker base than ammonia because:

Chemical Reactions: Acylation and Carbylamine

Acylation: RNH₂ + R'COCl/R'(CO)₂O → amide (N–acyl), useful protection of the amino group (acetylated against diazotisation attack).
Carbylamine test: 1° amine + CHCl₃ + KOH → isocyanide (R–NC), foul smell; positive only for primary amines.
With aldehydes/ketones: 1° amines form Schiff bases (imines) — the basis of many carbonyl-amine condensations.
Quaternisation: 3° amine + R–X → R₄N⁺X⁻ (permanent cation, used as phase-transfer catalysts, e.g. TEBA).

Carbylamine — identifies a primary amine

\ce R N H 2 + C H C l 3 + 3 K O H - > R - N C + 3 K C l + 3 H 2 O

Protection trick

Acetylating aniline (acetic anhydride) blocks the very reactive ring positions and the N–H, so a later nitration goes para instead of ortho — set up for a 5‑mark 'why protect?' question.

MCQ Questions

A foul-smelling isocyanide forms when a primary amine reacts with:

The product of RNH₂ with CH₃COCl is:

Reaction with Nitrous Acid and Diazonium Salts

1° aliphatic: HNO₂ → unstable diazonium, decomposes to alcohol/alkene.
1° aromatic (aniline): NaNO₂/HCl at 0–5 °C → benzene diazonium chloride (C₆H₅N₂⁺Cl⁻).
2° amines: give oily N‑nitrosamines (yellow).
3° aliphatic: no clean transformation; 3° aromatic → p‑nitroaryl products.

Definition

Reactions of diazonium salts

Replace N₂: Sandmeyer (CuCl/CuBr→chloro/bromoarene), Gattermann (Cu powder), KI→iodoarene, H₃PO₂→benzene, H₂O warm→phenol, CuCN→nitrile, ethanol→reduction. Keep the N₂: coupling with phenol/aniline forms brightly coloured azo dyes.

Cold + fresh

Diazotisation must run at 0–5 °C: above ~10 °C the salt decomposes into phenol and N₂. Freshly prepared salt is used immediately — exam questions love this.

MCQ Questions

Benzene diazonium chloride with CuCl gives:

Q10

Diazotisation of aniline is best carried out at:

Uses and Significance of Amines

Amines are the backbone of the biological and colour world: amino acids and proteins ARE amine chemistry; sulfa drugs, analgesics and local anaesthetics carry the group.

Dyes: aniline dyes and azo dyes from diazonium coupling colour fabrics and indicators (methyl orange).
Medicines: sulfanilamide antibiotics, adrenaline, levodopa; quaternary ammonium salts act as antiseptics.
Agriculture: aniline → herbicides; amine salts in fertiliser formulations.
Industrial: rubber accelerating agents, corrosion inhibitors, nylon precursors (hexamethylenediamine → nylon-66).

Biochemistry tie-in

α-Amino acids (RCH(NH₂)COOH) connect this chapter straight to Biomolecules — the amine end forms the peptide bond with the acid end of another amino acid.

MCQ Questions

Q11

Nylon-66 is made from a diacid and:

Q12

Azo dyes are obtained by coupling a diazonium salt with:

NCERT Exercise Questions

From the textbook

NCERT questions for this chapter, in textbook order. Answers are given at a glance below each set.

Exercises (NCERT Q1–Q3)

1
Arrange the following in increasing order of basicity in aqueous solution: Aniline, p‑nitroaniline, p‑toluidine.
2
What is the Hinsberg test? How does it distinguish between primary, secondary and tertiary amines?
3
Write the reaction of aniline with bromine water.

Answers at a glance

1
p‑Nitroaniline < Aniline < p‑Toluidine (increasing basicity).
2
Primary amine gives alkali‑soluble product; secondary gives alkali‑insoluble; tertiary does not react.
3
2,4,6‑Tribromoaniline is formed as a white precipitate.

CBSE Pattern Questions

How CBSE asks this chapter

CBSE generally asks 2-3 questions from Amines, focusing on nomenclature, classification, basicity, preparation methods and diazonium salt reactions.

MCQ Questions

Q13

Arrange the following in increasing order of basic strength in gaseous state: NH3, C2H5NH2, (C2H5)2NH, (C2H5)3N.

Q14

Which of the following amines gives a positive carbylamine reaction?

Q15

The aromatic amine that is diazotised most easily is:

Q16

The reaction of benzene sulphonyl chloride with primary amine followed by treatment with alkali gives:

1 Mark Questions

1
What is the Hoffmann bromamide degradation reaction?
2
Write the structure of Z‑but‑2‑ene.
3
Define primary amine.

2 Mark Questions

1
Explain why aniline does not undergo Friedel‑Crafts reaction.
2
How will you convert aniline to phenol?

3 Mark Questions

1
Describe the preparation of ethylamine by Gabriel phthalimide synthesis.
2
Explain the order of basicity of amines in aqueous solution.

5 Mark Questions

1
An organic compound (A) with molecular formula C3H9N on reaction with nitrous acid gives an alcohol and liberates N2 gas. Identify A.
2
Explain the following: (i) Why does dimethylamine give a positive carbylamine test? (ii) How will you distinguish between primary, secondary and tertiary amines using Hinsberg’s test?

PDF: Assignments & Tests

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Download topic-wise assignments and full CBSE-pattern tests with answer keys for this chapter.

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Class 12 Chemistry — downloadable assignments and CBSE-pattern tests (PDF).

Assignment 1 — Topic-wise Practice Set A

Topic-wise practice covering the first half of the chapter, with answer key.

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Assignment 2 — Topic-wise Practice Set B

Topic-wise practice covering the second half of the chapter, with answer key.

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CBSE Pattern Test 1

Full CBSE-pattern test (90 minutes, 40 marks) with answer key.

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CBSE Pattern Test 2

Second full CBSE-pattern test (90 minutes, 40 marks) with answer key.

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Quick Revision

Key formulas at a glance

Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.

General formulas

\ce R N H 2, R 2 N H, R 3 N, R 4 N + X -

1°, 2°, 3° amine + quaternary salt.

Ammonolysis

\ce R X + (e x cess) N H 3 - > R N H 2 + H X

Excess ammonia favours 1° amine.

Gabriel synthesis

\ce P h t ha l imi d e - K + + R X - > [(1) h y d r o l y s i s] R N H 2

Gives pure 1° amine, no 2°/3°.

Hofmann bromamide

\ce R C O N H 2 + B r 2 + 4 N a O H - > R N H 2 + 2 N a B r + N a 2 C O 3 + 2 H 2 O

Carbon count drops by one.

Carbylamine test

\ce R N H 2 + C H C l 3 + 3 K O H - > R - N C + 3 K C l + 3 H 2 O

1° amines only; foul isocyanide smell.

Aqueous basicity order

\ce 2^{°} > 1^{°} > 3^{°} > N H 3

Gas phase reverses to 3° > 2° > 1°.

Exam Strategy

How this chapter is asked

High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.

Classify 1°, 2°, 3° amines and quaternary salts; aromatic vs aliphatic.
Nomenclature: alkanamines, N-methyl prefix for 2°/3°, ‑amine vs ‑aniline aromatic names taken over from common names.
Ammonolysis with excess NH₃ — why the product mix, and why Gabriel avoids it (pure 1°).
Preparation wheel: nitro reduction, nitrile reduction, Hofmann bromamide degradation, reductive amination.
Basicity: aqueous order 2° > 1° > 3° > NH₃; gas phase 3° > 2° > 1°; substituent (+I/-I, +M/-M) effects on aniline.
Carbylamine test (isocyanides, 1° only) and quaternary ammonium salt formation.
Reaction with HNO₂: 1° → diazonium; 2° → N‑nitrosamine (yellow oil); aromatic 1° → diazonium salt.
Diazonium salts: Sandmeyer/Gattermann (CuX/Cu), KI, H₃PO₂, H₂O, CuCN, coupling to make azo dyes.
Hofmann elimination and exhaustive methylation of 3° amines.
Practical uses: dyes, sulfa drugs, amino acid backbone, polymers.

Practice Numericals

Step-by-step worked examples

Standard exam-level problems solved with clear conceptual breakdowns.

Strecker/ammonolysis purity trick

Problem StatementPrepare ethylamine cleanly from ethyl bromide avoiding 2° and 3° amines.

Step-by-Step Solution

1Direct ammonolysis gives a mixture because RNH₂ reacts again.
2Use Gabriel phthalimide: phthalimide potassium salt + ethyl bromide, then hydrazine/H⁺ hydrolysis.
3That delivers pure ethylamine by design.

Final Answer

Phthalimide-K⁺ + C₂H₅Br → hydrolysis → C₂H₅NH₂.

Aniline → benzene diazonium

Problem StatementWrite the diazotisation of aniline and one Sandmeyer product.

Step-by-Step Solution

1C₆H₅NH₂ + NaNO₂ + HCl at 0–5 °C → C₆H₅N₂⁺Cl⁻ + 2H₂O + NaCl.
2Add CuCl → chlorobenzene (Sandmeyer).
3Add KI → iodobenzene; add H₃PO₂ → benzene; add H₂O/warm → phenol.

Final Answer

C₆H₅N₂⁺Cl⁻, and with CuCl → C₆H₅Cl.

FAQ

Frequently asked questions

Why does Gabriel phthalimide make only a primary amine?

The phthalimide nitrogen carries two acyl groups that swallow both of its N–H hydrogens, leaving a nitrogen with exactly one alkylatable site. The potassium salt reacts once with RX and releases the single alkylamine on hydrolysis. There is no second N–H anywhere to make a 2° or 3° amine, so the product is 100% 1°.

What is the difference between the carbylamine and diazotisation tests?

Carbylamine (CHCl₃ + KOH) gives a foul-smelling isocyanide and is positive for primary amines only. Diazotisation uses NaNO₂ + HCl at low temperature: primary aromatic amines give diazonium salts; secondary amines give N‑nitrosamines (yellow oils); tertiary aliphatic amines give no clean product. Use carbylamine to confirm '1°' and diazotisation to confirm 'aromatic 1°'.

Why does the basicity order of amines change between water and the gas phase?

By inductive effect alone 3° > 2° > 1°. In water, hydration favours small ions — the more hydrogens the ammonium ion can donate, the better it solvates. Methyl substitution adds bulk and can block the O–H···N‑H⁺ approach. The two effects cross: aqueous 2° > 1° > 3°, gas phase 3° > 2° > 1°.

What makes aniline a useful starting material?

Its amino group is both activating and ortho/para-directing for electrophilic substitution and, after diazotisation, lets you daisy-chain the whole ring chemistry: Sandmeyer to haloarenes, CuCN to nitriles, H₃PO₂ to benzene, H₂O to phenol, and azo-coupling to coloured dyes. Nearly every substituted benzene in the syllabus routes through aniline.

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