Chapters

Everything NCERT Class 12 Unit 9 (Amines) says that can be asked, including its second part on diazonium salts, plus what JEE Main adds beyond the book (marked Beyond NCERT). The short note stays for the last week; this is for a proper revision pass.

Formula sheet

The rules the questions turn on, on one screen. Reagents are in the two maps and the named-reaction table below.

Rule or test	What it says	Watch
Basicity, gas phase	3° > 2° > 1° > NH₃	Pure +I effect
Basicity in water, methyl	(CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃	Solvation and crowding join in
Basicity in water, ethyl	(C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃	3° moves up for ethyl
Aryl amines	weaker bases than NH₃ (aniline pKb 9.38)	EDG on ring raises, EWG lowers
pKb	pKb = −log Kb; smaller pKb, stronger base	NH₃ 4.75
Carbon count	nitrile → amine: +1 C; Hoffmann: −1 C	Gabriel and LiAlH₄ on amides: same
Hoffmann	RCONH₂ + Br₂ + 4NaOH → RNH₂ + Na₂CO₃ + 2NaBr + 2H₂O	1 Br₂ and 4 NaOH per amide
Hinsberg	1° → sulphonamide soluble in alkali; 2° → insoluble; 3° → none	C₆H₅SO₂Cl or TsCl
Carbylamine	1° amines only (alkyl and aryl) → isocyanide	CHCl₃ + ethanolic KOH
Nitrous acid	1° aliphatic → ROH + N₂; 1° aromatic, 273–278 K → ArN₂⁺	1 mol N₂ per –NH₂
Coupling	phenol in mild alkali, aniline in mild acid; at para	Product keeps the N=N
Acetylation	each –NH₂ adds CH₃CO for H: +42 g mol⁻¹	Aniline 93 → acetanilide 135

0 · What JEE Main asks from this chapter

187 questions in JEE Main 2019–2026 (162 MCQ, 25 numerical), about 1 per paper. Grouped by type (counts are approximate; about 30 show the structures only as pictures):

Type	Share	Typical question
Preparation: reduction, Gabriel, Hoffmann, ammonolysis	~19%	Which amines can Gabriel synthesis make?
Tests: Hinsberg, carbylamine, nitrous acid	~17%	How many give alkali-insoluble sulphonamides?
Picture-only and long multi-step	~17%	Nitrobenzene through six steps: count the Br
Ring substitution of aniline, protection, yields	~14%	9.3 g aniline → tribromoaniline 26.4 g: % yield
Basicity and pKb order	~11%	Order of pyrrole, pyridine, piperidine
Diazonium replacements and sequences	~11%	Aniline → 1,3,5-tribromobenzene: the reagents
Coupling and azo dyes	~11%	Mass of aniline yellow from 279 g aniline

The numericals are almost all moles: aniline (93) to a product, N₂ volume to amine, π bonds or %N in a product.

1 · Structure and classification

Amines are derivatives of ammonia: one, two or three H replaced by alkyl or aryl groups.

• N is sp³, the molecule pyramidal. Three sp³ orbitals bond to H or C; the fourth holds the lone pair.
• The lone pair squeezes the C–N–E angle below 109.5°: 108° in trimethylamine (asked as a numerical in 2021).
• 1° RNH₂ (one H replaced), 2° R₂NH or RNHR′, 3° R₃N.
• Simple amine: all groups the same. Mixed: different.

2 · Nomenclature

• Common: alkyl group + amine as one word (methylamine); di or tri for repeated groups.
• IUPAC, 1°: replace the alkane's -e with amine: CH₃NH₂ is methanamine. Several –NH₂: number their carbons, add di, tri, and keep the e: H₂N–CH₂CH₂–NH₂ is ethane-1,2-diamine.
• IUPAC, 2° and 3°: the largest group is the parent; groups on N take the locant N.
• Arylamines: C₆H₅NH₂ is aniline (accepted by IUPAC) or benzenamine.

Amine	Common name	IUPAC name
CH₃CH₂NH₂	Ethylamine	Ethanamine
CH₃CH₂CH₂NH₂	n-Propylamine	Propan-1-amine
(CH₃)₂CHNH₂	Isopropylamine	Propan-2-amine
CH₃NHCH₂CH₃	Ethylmethylamine	N-Methylethanamine
(CH₃)₃N	Trimethylamine	N,N-Dimethylmethanamine
(C₂H₅)₂N(CH₂)₃CH₃	N,N-Diethylbutylamine	N,N-Diethylbutan-1-amine
CH₂=CHCH₂NH₂	Allylamine	Prop-2-en-1-amine
H₂N(CH₂)₆NH₂	Hexamethylenediamine	Hexane-1,6-diamine
o-CH₃C₆H₄NH₂	o-Toluidine	2-Methylaniline
p-BrC₆H₄NH₂	p-Bromoaniline	4-Bromobenzenamine
C₆H₅N(CH₃)₂	N,N-Dimethylaniline	N,N-Dimethylbenzenamine

3 · Preparation

1. Reduction of nitro compounds.
   • H₂ with finely divided Ni, Pd or Pt, or a metal in acid (Sn/HCl, Fe/HCl). Nitroalkanes reduce the same way.
   • Fe scrap + HCl is preferred: the FeCl₂ formed hydrolyses and releases HCl, so only a little acid is needed to start.
2. Ammonolysis of alkyl halides. An alkyl or benzyl halide + ethanolic NH₃ in a sealed tube at 373 K: SN substitution of X by –NH₂.
   • The 1° amine is itself a nucleophile, so it goes on to 2°, 3° and finally the quaternary ammonium salt. You get a mixture.
   • A large excess of NH₃ makes the 1° amine the major product.
   • The amine comes out as its salt, RNH₃⁺X⁻; a strong base (NaOH) frees it.
   • Reactivity of halides: RI > RBr > RCl.
3. Reduction of nitriles. LiAlH₄ or catalytic hydrogenation → 1° amine with one carbon more (ascent of the amine series).
4. Reduction of amides. LiAlH₄ → amine with the same carbons.
5. Gabriel phthalimide synthesis (1° amines only):
   • Phthalimide + ethanolic KOH → potassium phthalimide.
   • Heat with an alkyl halide → N-alkylphthalimide.
   • Alkaline hydrolysis → the 1° amine.
   • No aromatic amines: aryl halides don't undergo nucleophilic substitution by the phthalimide anion.
6. Hoffmann bromamide degradation. An amide + Br₂ in aqueous or ethanolic NaOH. An alkyl or aryl group migrates from the carbonyl carbon to N; the amine has one carbon less.

Example (NCERT Example 9.1) · C₂H₅Cl + ethanolic NH₃ → C₂H₅NH₂ (with C₂H₅NH₃⁺Cl⁻). Benzyl chloride → benzylamine; + 2 CH₃Cl → N,N-dimethylbenzylamine (C₆H₅CH₂N(CH₃)₂).

Example (NCERT Example 9.2) · CH₃CH₂Cl → (KCN) CH₃CH₂CN → (LiAlH₄) propan-1-amine. C₆H₅CH₂Cl → (KCN) → (reduction) 2-phenylethanamine. Each adds one carbon.

Example (NCERT Example 9.3) · Propanamine by Hoffmann needs a 4-carbon amide: butanamide. Benzamide gives aniline.

Example (2021) · Gabriel synthesis works for (CH₃)₂CHCH₂NH₂, CH₃CH₂NH₂ and C₆H₅CH₂NH₂, but not aniline: 3. In 2019, n-butylamine yes; t-butylamine and neopentylamine no.

Example (2025) · 11.25 mg chlorobenzene (112.5) = 0.1 mmol → (Mg; CO₂, H₃O⁺) benzoic acid → (NH₃, Δ) benzamide → (Br₂, NaOH) aniline = 0.1 mmol × 93 = 9.3 mg → 93 (× 10⁻¹ mg).

Fine print on these methods · Beyond NCERT

• Gabriel is SN2: it fails for 3° halides (t-butylamine) and is very slow for neopentyl. Hydrazine also frees the amine from N-alkylphthalimide (2019).
• Hoffmann's intermediate is the isocyanate R–N=C=O (2022). The lost carbonyl carbon leaves as CO₃²⁻ (2021). The migrating group keeps its configuration.
• Nitrobenzene → aniline: Sn/HCl, Fe/HCl, Zn/HCl, H₂/Pd and H₂/Raney Ni all work; Sn/NH₄OH does not (2021: 5).
• Nitriles → amines need LiAlH₄ or H₂/Ni (or Na/C₂H₅OH); NaBH₄ fails (2020).

4 · Physical properties

• The lower aliphatic amines are gases with a fishy odour. 1° amines with three or more carbons are liquids; higher ones solids.
• Aniline and other arylamines are colourless but darken on storage: atmospheric oxidation (2023: "reduction" was the trap).
• Solubility: lower aliphatic amines dissolve in water (H-bonds with water); solubility falls as the alkyl part grows. All dissolve in alcohol, ether, benzene. Alcohols are more polar than amines (O is 3.5, N 3.0), so butan-1-ol is more soluble than butan-1-amine.
• Boiling point of isomers: 1° > 2° > 3°. A 1° amine has two N–H to H-bond with, a 2° amine one, a 3° amine none.

Compound (M ≈ 73)	b.p. (K)
n-C₄H₉NH₂	350.8
(C₂H₅)₂NH	329.3
C₂H₅N(CH₃)₂	310.5
C₂H₅CH(CH₃)₂ (alkane, 72)	300.8
n-C₄H₉OH (74)	390.3

Example (2026) · Increasing b.p.: n-butane < diethylamine < n-butylamine < n-butanol.

5 · Basicity

Amines are Lewis bases (lone pair on N). With acids they form salts; NaOH gives back the amine. The salts dissolve in water but not in ether, which separates amines from non-basic compounds.

Larger Kb, smaller pKb: stronger base.

Amine	pKb
N-Ethylethanamine (C₂H₅)₂NH	3.00
N,N-Diethylethanamine (C₂H₅)₃N	3.25
N-Methylmethanamine (CH₃)₂NH	3.27
Ethanamine C₂H₅NH₂	3.29
Methanamine CH₃NH₂	3.38
N,N-Dimethylmethanamine (CH₃)₃N	4.22
Phenylmethanamine C₆H₅CH₂NH₂	4.70
Ammonia	4.75
N,N-Dimethylaniline	8.92
N-Methylaniline	9.30
Benzenamine (aniline)	9.38

Alkylamines vs NH₃. Alkyl groups push electrons to N (+I) and spread the cation's + charge, so alkylamines are stronger bases (pKb 3 to 4.22).

• Gas phase: the +I order holds: 3° > 2° > 1° > NH₃.
• Water: the cation is also stabilised by H-bonding to water (solvation). RNH₃⁺ has three N–H to H-bond with, R₃NH⁺ only one, so solvation alone would give 1° > 2° > 3°.
• Crowding: a group bigger than CH₃ also blocks the H-bonding.
• The balance of the three gives:

Arylamines vs NH₃. In aniline the lone pair is conjugated with the ring (five resonance structures), so it is less available. The anilinium ion has only two (Kekulé) structures. Aniline is stabilised more than its cation, so it is a much weaker base than NH₃.

• EDG on the ring (–OCH₃, –CH₃) raise basicity.
• EWG (–NO₂, –SO₃H, –COOH, –X) lower it.
• Benzylamine (CH₂ between ring and N) behaves like an alkylamine (4.70).

Example (NCERT Example 9.4, Intext 9.4) · (C₂H₅)₂NH > C₂H₅NH₂ > NH₃ > C₆H₅NH₂. And C₆H₅NH₂ < C₆H₅CH₂NH₂ < (CH₃)₃N < CH₃NH₂ < (CH₃)₂NH.

Example (2025) · Of 4-nitroaniline, phenylmethanamine, N-phenylethanamide and 2-methylaniline, the most basic is phenylmethanamine (107). 1.0 g = 9.35 mmol, which takes 9.35 × 36.5 = 341 mg HCl.

Example (NCERT exercise 9.3) · Methylamine in water precipitates hydrated ferric oxide from FeCl₃: it is a stronger base than water and supplies OH⁻.

More basicity orders · Beyond NCERT

• Amides are barely basic: the lone pair goes into the C=O. Acetamide is weaker than aniline (2021); (CH₃CO)₂NH is the least basic of all (2021).
• Hydrazine < NH₃ (2025): the −I of the second N.
• Heterocycles: piperidine (sp³ N) > pyridine (sp² N, lone pair not in the ring) > pyrrole (lone pair is part of the aromatic sextet). Cyclohexylamine > pyridine > aniline > pyrrole (2020).
• Ortho effect: almost any ortho group makes aniline a weaker base (crowding hinders the cation's solvation).

6 · Reactions of amines

Alkylation. With alkyl halides (as in ammonolysis), up to the quaternary salt.

Example (2021) · 0.1 mol benzylamine gave 23 g benzyltrimethylammonium bromide (C₁₀H₁₆NBr, 230) = 0.1 mol. Three CH₃ were added, so CH₃Br used = 0.3 mol (n = 3).

Acylation. 1° and 2° amines (aliphatic and aromatic) react with acid chlorides, anhydrides and esters by nucleophilic substitution: the N–H hydrogen is replaced by an acyl group, giving an amide. A base stronger than the amine, such as pyridine, removes the HCl and drives it forward. With benzoyl chloride it is benzoylation: CH₃NH₂ + C₆H₅COCl → C₆H₅CONHCH₃ (N-methylbenzamide). With carboxylic acids at room temperature, amines only form salts.

Example (2024) · 9.3 g aniline = 0.1 mol → acetanilide (135) = 13.5 g. A compound of M 108 that acetylates to M 192 gained 84 = 2 × 42, so it has 2 –NH₂ (phenylenediamine).

Acylation goes to N first · Beyond NCERT · An –NH₂ is a better nucleophile than an –OH in the same molecule. 4-Aminophenol + acetic anhydride → paracetamol (N-acetyl); an amino alcohol + ethyl formate → the N-formyl compound (2019, 2021).

Carbylamine reaction (isocyanide test). 1° amines, aliphatic and aromatic, heated with CHCl₃ and ethanolic KOH give isocyanides (carbylamines): foul-smelling. 2° and 3° amines don't. It is the test for a 1° amine.

Nitrous acid (made in the flask from NaNO₂ and a mineral acid):

• 1° aliphatic: an unstable alkyldiazonium salt that gives off N₂ quantitatively and an alcohol. The N₂ volume is used to estimate amino acids and proteins.
• 1° aromatic, at 273–278 K: an arenediazonium salt (section 7).
• 2° and 3° amines react differently.

Example (2024) · Ethylamine + NaNO₂/HCl gave 2.24 L N₂ at STP = 0.1 mol. So ethylamine = 0.1 mol × 45 = 4.5 g → 45 (× 10⁻¹ g).

2° and 3° amines with HNO₂ · Beyond NCERT · A 2° amine gives a yellow oily N-nitrosamine R₂N–N=O. A 3° aliphatic amine just forms a salt. N,N-Dimethylaniline is nitrosated on the ring at para (electrophile NO⁺; 2023). The alkyl cation from a 1° aliphatic amine can rearrange: a ring CH₂NH₂ can expand the ring by one (2019, 2021).

Hinsberg's reagent (benzenesulphonyl chloride, C₆H₅SO₂Cl):

Amine	Product	In alkali
1°	N-alkylbenzenesulphonamide, C₆H₅SO₂NHR	Soluble: the N–H is strongly acidic (next to SO₂)
2°	N,N-dialkylbenzenesulphonamide, C₆H₅SO₂NR₂	Insoluble: no N–H
3°	No reaction	—

It distinguishes and separates the three classes. Today p-toluenesulphonyl chloride (TsCl) is used instead.

Example (2026) · Alkali-insoluble sulphonamides among 11 amines: only the 2° ones count. N-methylaniline, N-methylmethanamine, N-propylaniline, N-phenylaniline: 4.

Example (2024) · Benzyl chloride + NH₃ gives an amine that leaves TsCl solution clear: a 3° amine, tribenzylamine (C₆H₅CH₂)₃N = 287 g mol⁻¹.

Example (2026) · X: C 61.01%, H 15.25%, N 23.74% → C₃H₉N. HNO₂ gives a nitrogen-free alcohol whose oxidation product gives iodoform: X is isopropylamine → propan-2-ol → acetone.

Electrophilic substitution in aniline. The resonance structures put high electron density at ortho and para: –NH₂ is a powerful activating, o/p-directing group.

• (a) Bromination: bromine water at room temperature → white precipitate of 2,4,6-tribromoaniline at once.
• Controlling it: protect –NH₂ by acetylation with acetic anhydride, substitute, then hydrolyse the amide back. In acetanilide the N lone pair is shared with the C=O, so –NHCOCH₃ activates less than –NH₂. Aniline → acetanilide → (Br₂, CH₃COOH) p-bromoacetanilide → (H⁺ or OH⁻) p-bromoaniline.
• (b) Nitration: direct nitration gives tarry oxidation products. In the strong acid, aniline is protonated to the anilinium ion, which is meta-directing, so a large amount of the meta product forms: p 51%, m 47%, o 2%. Protect by acetylation to get the p-nitro product as the major one.
• (c) Sulphonation: aniline + conc. H₂SO₄ → anilinium hydrogensulphate; heating at 453–473 K gives sulphanilic acid (p-aminobenzenesulphonic acid).
• No Friedel–Crafts (alkylation or acylation): aniline forms a salt with AlCl₃, the N becomes positive, and it deactivates the ring.

Example (2024) · 9.3 g aniline (0.1 mol) with bromine water → theoretical 0.1 × 330 = 33 g tribromoaniline; 26.4 g obtained → 80%.

Example (2026) · Benzene → nitrobenzene → aniline → acetanilide → p-nitroacetanilide → (acid hydrolysis) p-nitroaniline C₆H₆N₂O₂ (138): %N = 28/138 × 100 = 20%.

More ring tricks · Beyond NCERT

• Ortho product: block para with –SO₃H first. Aniline → H₂SO₄ (SO₃H at para) → Ac₂O → Br₂ (ortho) → H₂O, heat (removes the SO₃H) → NaOH (removes the acetyl) gives 2-bromoaniline (2025).
• Statement pairs (2022, 2026): in nitration "H₂SO₄ acts as the acid"; m-nitroaniline exceeds o-nitroaniline.
• Sulphanilic acid is a zwitterion (H₃N⁺–C₆H₄–SO₃⁻) and gives the blood-red colour in Lassaigne's test (N and S together; 2024).

7 · Diazonium salts

Formula and names. ArN₂⁺X⁻ (X⁻ = Cl⁻, Br⁻, HSO₄⁻, BF₄⁻ …). The –N₂⁺ group is the diazonium group. Name: parent hydrocarbon + diazonium + anion: C₆H₅N₂⁺Cl⁻ is benzenediazonium chloride; C₆H₅N₂⁺HSO₄⁻ is benzenediazonium hydrogensulphate.

Stability. Alkyldiazonium salts are highly unstable. Arenediazonium salts last a short time in cold solution (273–278 K): resonance with the ring stabilises them.

Diazotisation. Aniline + nitrous acid (NaNO₂ + HCl, made in the flask) at 273–278 K. The salt is not stored; it is used at once.

Physical properties. Benzenediazonium chloride is a colourless crystalline solid, readily soluble in water, stable in the cold, reacts with water when warmed, and decomposes easily when dry. Benzenediazonium fluoroborate is water-insoluble and stable at room temperature.

Diazonium stability order · Beyond NCERT · An EDG para to –N₂⁺ stabilises it; an EWG destabilises: p-OCH₃ > H > p-CN > p-NO₂ (2022). p-Toluidine gives a more stable salt than any aliphatic amine (2021).

A. N₂ is replaced (–N₂⁺ is an excellent leaving group; N₂ escapes as gas):

1. Cl, Br, CN with Cu(I): Sandmeyer reaction. CuCl/HCl → ArCl; CuBr/HBr → ArBr; CuCN/KCN → ArCN.
2. Cl, Br with copper powder + HX: Gattermann reaction. Sandmeyer gives the better yield.
3. I: aqueous KI → ArI. Iodine can't be put on the ring directly.
4. F: HBF₄ precipitates the diazonium fluoroborate; heating it gives ArF + BF₃ + N₂.
5. H: mild reducing agents, hypophosphorous acid (H₃PO₂, phosphinic acid) or ethanol, give the arene. They are oxidised to phosphorous acid and ethanal.
6. OH: let the solution warm to 283 K: it hydrolyses to phenol.
7. NO₂: heat the fluoroborate with aqueous NaNO₂ and Cu → ArNO₂.

B. N₂ is kept: coupling. The diazonium ion is the electrophile (electrophilic substitution) and attacks para to –OH or –NH₂. The product has two rings joined by –N=N–: an extended conjugated system, often coloured, used as a dye.

• With phenol (mildly alkaline) → p-hydroxyazobenzene, an orange dye.
• With aniline (mildly acidic) → p-aminoazobenzene (aniline yellow).

Example (2024) · 9.3 g aniline (0.1 mol) → diazotise → couple with phenol → p-hydroxyazobenzene C₁₂H₁₀N₂O (198): 19.8 ≈ 20 g. And 279 g aniline (3 mol) + benzenediazonium chloride → aniline yellow C₁₂H₁₁N₃ (197): 3 × 197 = 591 g.

Why diazonium salts matter. They put F, Cl, Br, I, CN, OH and NO₂ on a ring where direct substitution can't: ArF and ArI can't be made by direct halogenation, and Cl in chlorobenzene can't be replaced by CN⁻, but cyanobenzene comes easily from the diazonium salt. The NH₂ can also be used as a temporary director and then removed.

Example (NCERT Example 9.5) · 4-Nitrotoluene → 2-bromobenzoic acid. Br₂/Fe brominates ortho to CH₃. Sn/HCl turns –NO₂ into –NH₂. NaNO₂/HCl then H₃PO₂ removes it. KMnO₄ oxidises CH₃ → COOH.

Example (NCERT Intext 9.9, asked in 2022) · Aniline → Br₂ water → 2,4,6-tribromoaniline → NaNO₂/HCl → H₃PO₂ → 1,3,5-tribromobenzene: a pattern no direct bromination gives.

Example (2026) · Nitrobenzene → Br₂/FeBr₃ (m-bromo) → Sn/HCl (3-bromoaniline) → Br₂ water (Br at 2, 4, 6) → diazotise → CuBr: 5 Br in the product.

More coupling · Beyond NCERT

• β-Naphthol in NaOH couples at C-1 to a scarlet-red dye: the confirmatory test for a 1° aromatic amine (2024). Benzylamine and N-methylaniline don't give it (2021).
• N,N-Dimethylaniline couples at para → p-(dimethylamino)azobenzene (butter yellow).
• Sulphanilic acid + 1-naphthylamine → a red azo dye (2023–2025).
• Diazoaminobenzene (PhN=N–NHPh, the N-coupled product) rearranges in acid with excess aniline to p-aminoazobenzene (C₁₂H₁₁N₃, %N = 42/197 = 21%; 2026).

8 · Named reactions

Name	Reagents	Change
Ammonolysis	NH₃ (ethanolic), 373 K, sealed tube	RX → RNH₂ (+ 2°, 3°, R₄N⁺X⁻)
Gabriel phthalimide synthesis	phthalimide, KOH; RX; NaOH (aq)	RX → RNH₂ (1° alkyl only)
Hoffmann bromamide degradation	Br₂, NaOH	RCONH₂ → RNH₂, one C less
Carbylamine reaction	CHCl₃, KOH (alc.), Δ	RNH₂ → RNC (foul smell)
Hinsberg test	C₆H₅SO₂Cl (or TsCl), then alkali	sorts 1°, 2°, 3°
Acylation / benzoylation	(CH₃CO)₂O or C₆H₅COCl, pyridine	RNH₂ → RNHCOR′
Diazotisation	NaNO₂ + HCl, 273–278 K	ArNH₂ → ArN₂⁺Cl⁻
Sandmeyer reaction	CuCl, CuBr, CuCN	ArN₂⁺ → ArCl, ArBr, ArCN
Gattermann reaction	Cu powder + HCl / HBr	ArN₂⁺ → ArCl, ArBr
Balz–Schiemann (Beyond NCERT, the name)	HBF₄; heat	ArN₂⁺ → ArF
Coupling	phenol (OH⁻) or aniline (H⁺)	→ Ar–N=N–Ar′ (azo dye)

9 · Traps

Trap	What goes wrong	Do this
Gabriel and aniline	Making aryl amines by Gabriel (2021)	Aryl halides don't do SN; Gabriel gives 1° alkyl (and benzyl) amines only
Hoffmann on benzamide	Writing benzylamine (2026)	One C less: aniline
Hoffmann stoichiometry	2 Br₂ per amide (2026)	1 Br₂, 4 NaOH; by-products Na₂CO₃, NaBr, H₂O
Basicity in water	Using the gas-phase order	Methyl: 2° > 1° > 3°; ethyl: 2° > 3° > 1°
Benzylamine	Treating it as an arylamine	N is on CH₂, not the ring: pKb 4.70, near NH₃
Nitration of aniline	Expecting only o/p (2021, 2022)	Anilinium is meta-directing: m is 47%
Friedel–Crafts on aniline	Expecting o/p-methylaniline (2022)	No reaction: AlCl₃ salt deactivates the ring
Hinsberg with 3° amines	Counting (C₆H₅)₃N as reacting (2024)	3° amines don't react; 2° give alkali-insoluble solids
Carbylamine	Counting 2° amines (2025)	1° only, aryl included
Colour of stored aniline	"Reduction" (2023)	Atmospheric oxidation
Phenol from diazonium	Heating strongly	Just warm to 283 K in water
Coupling medium	Phenol in acid, aniline in alkali	Phenol: mildly alkaline; aniline: mildly acidic

10 · Numbers worth knowing

• pKb: NH₃ 4.75; aniline 9.38; (C₂H₅)₂NH 3.00; CH₃NH₂ 3.38; benzylamine 4.70.
• C–N–C angle in trimethylamine 108°. Diazotisation at 273–278 K; phenol forms at 283 K; sulphonation at 453–473 K; ammonolysis at 373 K.
• Nitration of aniline: p 51%, m 47%, o 2%.

Compound	g mol⁻¹
aniline	93
benzylamine	107
acetanilide	135
benzamide	121
p-nitroaniline	138
benzanilide	197
p-aminoazobenzene (aniline yellow)	197
p-hydroxyazobenzene	198
2,4,6-tribromoaniline	330
ethylamine	45

11 · For the boards only

JEE Main doesn't ask this, but the CBSE paper can.

• Amines occur in proteins, vitamins, alkaloids and hormones; synthetic ones in polymers, dyes and drugs.
• Adrenaline and ephedrine (both 2° amines) raise blood pressure.
• Novocain is a local anaesthetic in dentistry. Benadryl, an antihistamine, has a 3° amino group.
• Quaternary ammonium salts are surfactants. Trimethylamine is an insect attractant.
• Diazonium salts are intermediates for dyes and many aromatic compounds.