Amines are organic derivatives of ammonia in which one, two or three hydrogen atoms are replaced by alkyl or aryl groups, giving primary, secondary and tertiary amines whose chemistry is driven by the lone pair on nitrogen. The chapter covers their classification and nomenclature, preparation routes (reduction, ammonolysis, Gabriel and Hoffmann bromamide), physical properties, basicity trends, characteristic reactions, and the versatile aryl diazonium salts. It is a high-yield NEET topic because basicity comparisons, identification tests and diazonium conversions appear almost every year.
Class 12 Chemistry · Amines – swipe through all 10 cards to understand the whole chapter.
What Amines Are
Amines are ammonia (NH3) with one or more H atoms replaced by alkyl/aryl groups.
N is sp3, pyramidal, with a lone pair that drives basicity & nucleophilicity.
- Class = how many CARBONS attach to N (not the carbon type)
- tert-butylamine & benzylamine are 1° — only one C on N
- The lone pair is the engine of every reaction in this chapter
Nomenclature
IUPAC drops the -e of the alkane and adds -amine; groups on N take an N- prefix.
Common names list groups + ‘amine’ as one word (e.g. ethylmethylamine).
- (CH3)2CH−NH2 → propan-2-amine (1°)
- C2H5−NH−CH3 → N-methylethanamine
- Aniline = aminobenzene = benzenamine (fixed name)
Preparing Amines
Five NEET routes — and three of them quietly change the carbon count.
Ammonolysis (R−X + NH3) is non-selective → gives a 1°/2°/3°/quaternary mixture.
- Nitrile R−C≡N →(H2/Ni) R−CH2−NH2 — GAINS one carbon
- Amide →(LiAlH4) amine — SAME carbon count
- NaNO2/HCl is diazotisation, NOT reduction — don’t confuse
Gabriel vs Hoffmann
Two famous routes to pure 1° amines, each with a classic exam trap.
Hoffmann expels the carbonyl carbon as carbonate → amine has ONE C less than the amide.
- Gabriel → pure 1° amine; FAILS for aryl amines (no SN2 on aryl halides)
- Hoffmann bromamide → loses one carbon
- Propanamide (3C) →Hoffmann→ ethanamine (2C)
Boiling Point & Solubility
Boiling point tracks the number of N–H bonds available for hydrogen bonding.
3° amines boil lowest — no N–H to donate, not because they’re less polar.
- Across families: alcohol > amine > ether ≈ alkane (O more electronegative than N)
- 3° amines still dissolve in water — lone pair accepts H-bond (N···H−O)
- Solubility falls as the carbon chain grows; lower amines smell fishy
Basicity in Water
A base donates its N lone pair to a proton; in water, solvation breaks the simple trend.
Lower pK_b (higher K_b) = stronger base. Gas-phase order is the regular 3°>2°>1°>NH3.
- +I effect of alkyl groups makes aliphatic amines stronger than NH3
- 3° drops below 1° in water: poor solvation + steric crowding
- Aryl > don’t apply +I here — see the next card
Why Aniline Is Weak
In aniline the N lone pair is delocalised into the benzene ring, so it’s less available.
Weakness is from resonance delocalisation, not any inductive effect.
- Electron-withdrawing −NO2 on the ring → even weaker base
- Electron-donating −CH3 / −OCH3 → stronger base
- p-nitroaniline ≪ aniline < p-toluidine
Identifying the Class
Two tests pin down whether an amine is 1°, 2° or 3°.
Carbylamine test is POSITIVE for 1° amines only; needs ALCOHOLIC KOH.
- Hinsberg (C6H5SO2Cl): 1° → soluble in KOH, 2° → insoluble, 3° → no reaction
- 3° amines can’t be acylated (no N–H) and give no carbylamine test
- 1° & 2° amines acylate with acid chlorides/anhydrides → amides
Reactions of Aniline
The −NH2 group is strongly activating and o/p-directing, so the ring is very reactive.
To stop at mono-substitution, acetylate first (−NH2 → −NHCOCH3), then hydrolyse.
- 1° aromatic amine + HNO2 at 0–5 °C → stable diazonium salt
- 1° aliphatic amine + HNO2 → alcohol + brisk N2 gas
- Acetylation also protects N from oxidation
Diazonium Salts
Aryl diazonium salt acts like a universal adapter — −N2⁺ swaps for almost any group.
Cold (0–5 °C) is non-negotiable; warming gives phenol + N2. Only ARYL salts are usable.
- Sandmeyer: −Cl/−Br (CuCl/CuBr), −CN (CuCN); −I needs only KI (no Cu)
- −F via Balz–Schiemann (HBF4, heat); −OH via warm water; −H via H3PO2
- Coupling with phenol/aniline → azo dye (−N=N−) at para position
📝 Practice Amines — 10 NEET PYQs
Real previous-year questions · with answers & solutions
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- Aldehydes, Ketones and Carboxylic Acids Class 12 Notes
- Alcohols, Phenols and Ethers Class 12 Notes
- Biomolecules Class 12 Notes
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Frequently Asked Questions
Amines are derivatives of ammonia (NH3) in which one or more hydrogen atoms are replaced by alkyl or aryl groups. They are classified as primary (R-NH2), secondary (R2NH) or tertiary (R3N) based on how many carbon atoms are attached to the nitrogen, not on the type of carbon.
A primary aromatic amine like aniline is treated with sodium nitrite and HCl (nitrous acid) at 273 to 278 K (0 to 5 degrees C) in a reaction called diazotisation, giving C6H5N2+Cl-. The low temperature is essential because warm solutions decompose the diazonium salt into phenol and nitrogen gas.
In aniline the lone pair on nitrogen is delocalised into the benzene ring through resonance, so it is less available to accept a proton. This makes aniline a weaker base than NH3 and much weaker than aliphatic amines, which are strengthened by the electron-donating inductive effect of alkyl groups.
The Gabriel phthalimide synthesis gives pure primary amines but fails for aromatic amines because aryl halides do not undergo the required nucleophilic substitution. The Hoffmann bromamide reaction converts an amide to a primary amine using Br2 and KOH and produces an amine with one carbon fewer than the starting amide.
Yes, Amines is a regularly tested NEET chapter from Class 12 Organic Chemistry. The most frequently asked areas are basicity comparisons in water versus gas phase, identification tests like carbylamine and Hinsberg, and the substitution and coupling reactions of diazonium salts.