JEE Mains Chemistry · Teaching notes

Amines — JEE Mains Chemistry

Amines has 160 past-year questions from 2021 to 2026, and 24 of them ask for a number. The numbers are short stoichiometry: grams of acetanilide or dye from a given mass of aniline, litres of nitrogen from an aliphatic amine, the percentage of nitrogen in a product, or how many amines in a list pass a test. Everything else turns on one lone pair: how freely it takes a proton, how strongly it activates a benzene ring, and what becomes of the nitrogen once it is a diazonium ion. Multistep sequences are common, so learn each reagent together with the carbon count and the ring position it leaves behind.

Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.

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Subtopic notes

Formula & revision sheet

15 formulas · 6 reference tables · 45 gotchas across all subtopics — the exam-eve cheat-sheet

Structure, Physical Properties and Basicity

Formulas (2)

Basic strength of aliphatic amines and amides · Base dissociation of an amine and its pKb $\mathrm{RNH_2 + H_2O \rightleftharpoons RNH_3^+ + OH^-} \qquad K_b = \dfrac{[\mathrm{RNH_3^+}][\mathrm{OH^-}]}{[\mathrm{RNH_2}]} \qquad pK_b = -\log K_b$
Basic strength of aryl amines and nitrogen heterocycles · A base and its conjugate acid at 298 K $pK_a(\mathrm{BH^+}) + pK_b(\mathrm{B}) = 14$

Reference tables (1)

Structure and physical properties of amines6 rows

Property	What is observed	Reason
Shape at nitrogen	Pyramidal, C–N–C about 108° in $\mathrm{(CH_3)_3N}$	$sp^3$ nitrogen with one lone pair
Physical state	Lower aliphatic amines are gases with a fishy smell; 1° amines with three or more carbons are liquids	Molar mass and hydrogen bonding rise together
Boiling point of isomers	1° > 2° > 3°	Two N–H, one N–H, then no N–H for intermolecular hydrogen bonds
Amine against alcohol	Alcohol boils higher at similar molar mass	O–H is more polar than N–H, so its hydrogen bonds are stronger
Solubility in water	Lower amines dissolve; higher amines and aniline barely dissolve	Hydrogen bonds to water, outweighed by a large hydrophobic part
Aniline on storage	Colourless when pure, turns brown on standing	Atmospheric oxidation of the activated ring

Count the N–H bonds first: they decide hydrogen bonding, and hydrogen bonding decides boiling point.

Watch out for (7)

Primary amines associate more than secondary amines
→ Structure and physical properties of amines
Aniline darkens by oxidation, not reduction
→ Structure and physical properties of amines
Tertiary is not the strongest base in water
→ Basic strength of aliphatic amines and amides
The methyl and ethyl orders are different
→ Basic strength of aliphatic amines and amides
An amide is not an amine
→ Basic strength of aliphatic amines and amides
Benzylamine is not an aryl amine for basicity
→ Basic strength of aryl amines and nitrogen heterocycles
Pyridine and pyrrole are not equally basic
→ Basic strength of aryl amines and nitrogen heterocycles

Preparation: Reduction, Ammonolysis and Gabriel Synthesis

Formulas (2)

Ammonolysis of alkyl halides · Successive alkylation in ammonolysis $\mathrm{NH_3 \xrightarrow{RX} RNH_2 \xrightarrow{RX} R_2NH \xrightarrow{RX} R_3N \xrightarrow{RX} R_4N^+X^-}$
Gabriel phthalimide synthesis of primary amines · Gabriel phthalimide synthesis $\text{phthalimide} \xrightarrow{\mathrm{KOH}} \text{K-phthalimide} \xrightarrow{\mathrm{RX}} \text{N-alkylphthalimide} \xrightarrow{\mathrm{NaOH(aq)}} \mathrm{RNH_2} + \text{phthalate}$

Reference tables (1)

Reduction routes to amines: nitro compounds, nitriles and amides5 rows

Starting compound	Reagent	Product	Carbon count
$\mathrm{C_6H_5NO_2}$	$\mathrm{Sn/HCl}$ , $\mathrm{Fe/HCl}$ or $\mathrm{H_2/Pd}$	$\mathrm{C_6H_5NH_2}$	Unchanged
$\mathrm{RC{\equiv}N}$	$\mathrm{LiAlH_4}$ , $\mathrm{H_2/Ni}$ or $\mathrm{Na(Hg)/C_2H_5OH}$	$\mathrm{RCH_2NH_2}$	One more than the halide RX
$\mathrm{RCONH_2}$	$\mathrm{LiAlH_4}$ , then $\mathrm{H_2O}$	$\mathrm{RCH_2NH_2}$	Unchanged
$\mathrm{RC{\equiv}N}$	$\mathrm{SnCl_2/HCl}$ , then $\mathrm{H_3O^+}$	$\mathrm{RCHO}$ , not an amine	Unchanged
$\mathrm{RCONH_2}$	$\mathrm{Br_2}$ and NaOH (Hofmann)	$\mathrm{RNH_2}$	One fewer

Reduction keeps every carbon; only the Hofmann route drops one.

Watch out for (6)

Nitrobenzene needs acid or a catalyst to reach aniline
→ Reduction routes to amines: nitro compounds, nitriles and amides
Two amide reactions, two carbon counts
→ Reduction routes to amines: nitro compounds, nitriles and amides
Ammonolysis rarely gives one amine
→ Ammonolysis of alkyl halides
Ammonolysis breaks a C–X bond
→ Ammonolysis of alkyl halides
Gabriel gives no aryl amines
→ Gabriel phthalimide synthesis of primary amines
Gabriel gives no secondary amines
→ Gabriel phthalimide synthesis of primary amines

Hofmann Bromamide Degradation

Formulas (2)

Hofmann bromamide degradation: equation, intermediates and scope · Hofmann bromamide degradation $\mathrm{RCONH_2 + Br_2 + 4NaOH \to RNH_2 + Na_2CO_3 + 2NaBr + 2H_2O}$
Hofmann degradation in multistep sequences · Halide to amine with the same carbon count $\mathrm{RX \xrightarrow{Mg,\ ether} RMgX \xrightarrow{CO_2,\ H_3O^+} RCOOH \xrightarrow{NH_3,\ \Delta} RCONH_2 \xrightarrow{Br_2,\ NaOH} RNH_2}$

Watch out for (5)

Benzamide gives aniline, not benzylamine
→ Hofmann bromamide degradation: equation, intermediates and scope
Aryl groups migrate too
→ Hofmann bromamide degradation: equation, intermediates and scope
One bromine, four hydroxides
→ Hofmann bromamide degradation: equation, intermediates and scope
The Grignard route does not lengthen the amine
→ Hofmann degradation in multistep sequences
Isocyanides and nitriles hydrolyse differently
→ Hofmann degradation in multistep sequences

Acylation, Nitrous Acid and Hofmann Elimination

Formulas (2)

Acylation of amines: products, stoichiometry and yield · Acetylation of an amine and the mass it adds $\mathrm{RNH_2 + (CH_3CO)_2O \to RNHCOCH_3 + CH_3COOH} \qquad \Delta M = +42\ \mathrm{g\,mol^{-1}}\ \text{per acetyl group}$
Amine salts, nitrous acid on primary aliphatic amines, and Hofmann elimination · Nitrous acid on a primary aliphatic amine $\mathrm{RNH_2 \xrightarrow{NaNO_2,\ HCl,\ cold} [RN_2^+Cl^-] \xrightarrow{H_2O} ROH + N_2 + HCl} \qquad n(\mathrm{N_2}) = n(\mathrm{RNH_2})$

Watch out for (4)

Acylation is one to one per nitrogen
→ Acylation of amines: products, stoichiometry and yield
The better nucleophile is acylated first
→ Acylation of amines: products, stoichiometry and yield
Aliphatic and aromatic primary amines differ with nitrous acid
→ Amine salts, nitrous acid on primary aliphatic amines, and Hofmann elimination
Hofmann elimination is not Saytzeff elimination
→ Amine salts, nitrous acid on primary aliphatic amines, and Hofmann elimination

Carbylamine and Hinsberg Tests

Formulas (1)

Carbylamine (isocyanide) test for primary amines · Carbylamine reaction $\mathrm{RNH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} R{-}N{\equiv}C + 3KCl + 3H_2O}$

Reference tables (2)

Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines5 rows

Amine class	Example	Product with the reagent	Behaviour in alkali
Primary aliphatic	$\mathrm{C_2H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_2H_5}$	Dissolves: the N–H is acidic
Primary aromatic	$\mathrm{C_6H_5NH_2}$	$\mathrm{C_6H_5SO_2NHC_6H_5}$	Dissolves: the N–H is acidic
Secondary aliphatic	$\mathrm{(C_2H_5)_2NH}$	$\mathrm{C_6H_5SO_2N(C_2H_5)_2}$	Insoluble solid: no N–H left
Secondary aromatic	$\mathrm{C_6H_5NHCH_3}$	$\mathrm{C_6H_5SO_2N(CH_3)C_6H_5}$	Insoluble solid: no N–H left
Tertiary	$\mathrm{(C_2H_5)_3N}$ or $\mathrm{C_6H_5N(CH_3)_2}$	No reaction	The amine is unchanged

Reacts and dissolves: primary. Reacts and stays solid: secondary. No reaction: tertiary.

Identifying an amine from its test results5 rows

Test	Primary aliphatic	Primary aromatic	Secondary	Tertiary
$\mathrm{CHCl_3}$ + alcoholic KOH, heat	Foul-smelling isocyanide	Foul-smelling isocyanide	No isocyanide	No isocyanide
Hinsberg's reagent, then alkali	Sulphonamide, dissolves	Sulphonamide, dissolves	Sulphonamide, insoluble solid	No reaction
$\mathrm{NaNO_2}$ + HCl, cold	$\mathrm{N_2}$ gas and an alcohol	Diazonium salt, no gas at 273–278 K	N-Nitrosamine, yellow oil	Aliphatic: soluble salt; aromatic: p-nitroso compound
Diazotise, then β-naphthol in NaOH	No dye	Orange-red azo dye	No dye	No dye
Dilute HCl	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt	Dissolves as a salt

The dye test is the one that separates primary aromatic from primary aliphatic amines.

Watch out for (6)

The carbylamine test covers aromatic amines too
→ Carbylamine (isocyanide) test for primary amines
Isocyanide from a halide needs AgCN
→ Carbylamine (isocyanide) test for primary amines
A secondary amine's product does not dissolve in alkali
→ Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines
A clear solution means a primary amine
→ Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines
Dissolving in acid does not identify the class
→ Identifying an amine from its test results
Benzylamine behaves as an aliphatic amine in the tests
→ Identifying an amine from its test results

Electrophilic Substitution in Aniline

Formulas (2)

Bromination of aniline and protection by acetylation · Bromination of aniline with bromine water $\mathrm{C_6H_5NH_2 + 3Br_2 \xrightarrow{H_2O} 2,4,6{-}Br_3C_6H_2NH_2\downarrow + 3HBr}$
Nitration of aniline: the anilinium ion and meta product · Product distribution in the direct nitration of aniline $\mathrm{C_6H_5NH_2 \xrightarrow{HNO_3,\ H_2SO_4,\ 288\ K}}\ p\ (51\%) + m\ (47\%) + o\ (2\%)$

Reference tables (1)

Friedel–Crafts failure, sulphonation and oxidation of aniline5 rows

Reaction of aniline	Reagent and conditions	Result	Reason
Friedel–Crafts alkylation or acylation	RCl or RCOCl with anhydrous $\mathrm{AlCl_3}$	No ring substitution; N– $\mathrm{AlCl_3}$ complex	Nitrogen is a Lewis base; the complex deactivates the ring
Sulphonation	Conc. $\mathrm{H_2SO_4}$ , then 453–473 K	Sulphanilic acid, $\mathrm{H_3N^+C_6H_4SO_3^-}$	Anilinium hydrogensulphate rearranges on heating
Oxidation	Acidified $\mathrm{K_2Cr_2O_7}$	p-Benzoquinone	The ring is very electron-rich
Nitration	$\mathrm{HNO_3/H_2SO_4}$ , 288 K	Mixture of para, meta and ortho nitroanilines	Partial protonation to the anilinium ion
Bromination	Bromine water	2,4,6-Tribromoaniline	Strong activation by $\mathrm{NH_2}$

Wherever aniline meets an acid, think of the protonated or complexed nitrogen first.

Watch out for (6)

Bromine water cannot stop at one bromine
→ Bromination of aniline and protection by acetylation
The protecting group must come off
→ Bromination of aniline and protection by acetylation
NH₂ is not meta-directing
→ Nitration of aniline: the anilinium ion and meta product
Para is still slightly ahead of meta
→ Nitration of aniline: the anilinium ion and meta product
Friedel–Crafts on aniline gives no ring product at all
→ Friedel–Crafts failure, sulphonation and oxidation of aniline
A strongly activated ring is also easily oxidised
→ Friedel–Crafts failure, sulphonation and oxidation of aniline

Diazonium Salts: Stability and Replacement Reactions

Formulas (2)

Diazotisation and the stability of diazonium salts · Diazotisation of aniline $\mathrm{C_6H_5NH_2 + NaNO_2 + 2HCl \xrightarrow{273{-}278\ K} C_6H_5N_2^+Cl^- + NaCl + 2H_2O}$
Synthesis planning with diazonium salts: the amino group as a temporary director · Removing the amino group after it has directed $\mathrm{ArNH_2 \xrightarrow{NaNO_2,\ HCl,\ 273\ K} ArN_2^+Cl^- \xrightarrow{H_3PO_2,\ H_2O} ArH + N_2}$

Reference tables (1)

Replacement reactions of arenediazonium salts9 rows

Reagent	Product from ArN₂⁺	Name or note
$\mathrm{CuCl/HCl}$	ArCl	Sandmeyer
$\mathrm{CuBr/HBr}$	ArBr	Sandmeyer
$\mathrm{CuCN/KCN}$	ArCN	Sandmeyer
Cu powder with HCl or HBr	ArCl or ArBr	Gattermann
KI	ArI	No copper needed
$\mathrm{HBF_4}$ , then heat	ArF, with $\mathrm{BF_3}$ and $\mathrm{N_2}$	Balz–Schiemann
$\mathrm{H_2O}$ , warm	ArOH	Phenol and $\mathrm{N_2}$
$\mathrm{H_3PO_2}$ and $\mathrm{H_2O}$	ArH	Reductive removal; $\mathrm{H_3PO_3}$ forms
$\mathrm{CH_3CH_2OH}$	ArH	Ethanol is oxidised to ethanal

Sandmeyer delivers Cl, Br and CN only; F and I come by other reagents.

Watch out for (6)

Electron-withdrawing groups destabilise the diazonium salt
→ Diazotisation and the stability of diazonium salts
Only a nitrogen on the ring gives a stable salt
→ Diazotisation and the stability of diazonium salts
Ethanol reduces, it does not make an ether
→ Replacement reactions of arenediazonium salts
Fluoro- and iodobenzene are not Sandmeyer products
→ Replacement reactions of arenediazonium salts
The director is whatever is on the ring at that step
→ Synthesis planning with diazonium salts: the amino group as a temporary director
Removing NH₂ leaves the pattern it created
→ Synthesis planning with diazonium salts: the amino group as a temporary director

Coupling Reactions and Azo Dyes

Formulas (2)

Coupling of diazonium salts with phenols and aryl amines · Coupling of benzenediazonium chloride with phenol $\mathrm{C_6H_5N_2^+Cl^- + C_6H_5OH \xrightarrow{OH^-} C_6H_5{-}N{=}N{-}C_6H_4{-}OH\ (para) + HCl}$
Azo dye stoichiometry and the Griess–Ilosvay test · Mass of dye from the diazotised amine $n(\text{dye}) = n(\mathrm{ArNH_2}) \qquad m(\text{dye}) = n(\text{dye}) \times M(\text{dye}) \qquad \%\mathrm{N} = \dfrac{\text{mass of N}}{M} \times 100$

Watch out for (5)

Coupling keeps the nitrogen
→ Coupling of diazonium salts with phenols and aryl amines
Only strongly activated rings couple
→ Coupling of diazonium salts with phenols and aryl amines
Ortho methyls slow coupling on dimethylanilines
→ Coupling of diazonium salts with phenols and aryl amines
When aniline plays both roles, it is used twice
→ Azo dye stoichiometry and the Griess–Ilosvay test
The Griess–Ilosvay colour is red
→ Azo dye stoichiometry and the Griess–Ilosvay test

PYQ weightage by concept

21 concepts · 160 PYQs — where the marks actually sit, so you know what to drill first

Structure, Physical Properties and Basicity17 PYQs · 11%

Concept	PYQs	Share
Basic strength of aliphatic amines and amides	7	4%
Basic strength of aryl amines and nitrogen heterocycles	6	4%
Structure and physical properties of amines	4	3%

Preparation: Reduction, Ammonolysis and Gabriel Synthesis19 PYQs · 12%

Concept	PYQs	Share
Reduction routes to amines: nitro compounds, nitriles and amides	8	5%
Gabriel phthalimide synthesis of primary amines	7	4%
Ammonolysis of alkyl halides	4	3%

Hofmann Bromamide Degradation17 PYQs · 11%

Concept	PYQs	Share
Hofmann degradation in multistep sequences	11	7%
Hofmann bromamide degradation: equation, intermediates and scope	6	4%

Acylation, Nitrous Acid and Hofmann Elimination14 PYQs · 9%

Concept	PYQs	Share
Acylation of amines: products, stoichiometry and yield	8	5%
Amine salts, nitrous acid on primary aliphatic amines, and Hofmann elimination	6	4%

Carbylamine and Hinsberg Tests21 PYQs · 13%

Concept	PYQs	Share
Hinsberg test: benzenesulphonyl chloride with primary, secondary and tertiary amines	11	7%
Carbylamine (isocyanide) test for primary amines	5	3%
Identifying an amine from its test results	5	3%

Electrophilic Substitution in Aniline24 PYQs · 15%

Concept	PYQs	Share
Nitration of aniline: the anilinium ion and meta product	10	6%
Bromination of aniline and protection by acetylation	8	5%
Friedel–Crafts failure, sulphonation and oxidation of aniline	6	4%

Diazonium Salts: Stability and Replacement Reactions29 PYQs · 18%

Concept	PYQs	Share
Synthesis planning with diazonium salts: the amino group as a temporary director	13	8%
Replacement reactions of arenediazonium salts	12	8%
Diazotisation and the stability of diazonium salts	4	3%

Coupling Reactions and Azo Dyes19 PYQs · 12%

Concept	PYQs	Share
Coupling of diazonium salts with phenols and aryl amines	12	8%
Azo dye stoichiometry and the Griess–Ilosvay test	7	4%

Test yourself on Amines

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Structure, Physical Properties and Basicity

Preparation: Reduction, Ammonolysis and Gabriel Synthesis

Hofmann Bromamide Degradation

Acylation, Nitrous Acid and Hofmann Elimination

Carbylamine and Hinsberg Tests

Electrophilic Substitution in Aniline

Diazonium Salts: Stability and Replacement Reactions

Coupling Reactions and Azo Dyes

Formula & revision sheet

PYQ weightage by concept

Test yourself on Amines

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