Amines Class 12 Chapter Notes

Amines is a high-scoring CBSE Class 12 Organic Chemistry chapter because it connects basicity, preparation methods, chemical tests, diazonium salts and named reactions. These notes compress the chapter into exam-ready points: classification, nomenclature cues, preparation equations, basic strength trends, reactions of aliphatic and aromatic amines, and board-style traps. Revise this chapter by first memorising the reaction map, then comparing basicity orders, and finally practising tests like carbylamine and Hinsberg. Use YoLearn AI Tools to turn these notes into flashcards for named reactions, a mind map for conversions, a quiz for reagents and products, and a summarizer for last-minute equation recall. Focus especially on aniline, benzene diazonium chloride, Hoffmann bromamide degradation, Gabriel phthalimide synthesis, and azo coupling, as these frequently appear in short-answer and conversion questions.

Key points

Amines are derivatives of NH3 in which one or more H atoms are replaced by alkyl or aryl groups: RNH2, R2NH, R3N.
Basicity depends on +I effect, resonance, steric hindrance and solvation; do not use only inductive effect for aqueous order.
Aromatic amines are weaker bases than aliphatic amines because the lone pair on N is delocalised into the benzene ring.
Hoffmann bromamide degradation converts amide to a primary amine with one carbon less: RCONH2 to RNH2.
Gabriel phthalimide synthesis gives only primary aliphatic amines, not aromatic primary amines.
Carbylamine test is given only by primary amines, both aliphatic and aromatic, with CHCl3 and alcoholic KOH.
Aniline reacts with bromine water to give 2,4,6-tribromoaniline because -NH2 strongly activates the ring.
Diazonium salts of aromatic amines are stable only at low temperature, about 273-278 K, and are key intermediates for substitution and azo coupling.
Tertiary amines do not undergo acylation in the usual way because they have no N-H bond.
In conversions, protect -NH2 as acetanilide before controlled electrophilic substitution on aniline.

Definitions and exam terms

Amine: An organic derivative of ammonia in which one, two or three hydrogen atoms of NH3 are replaced by alkyl or aryl groups.
Primary amine: An amine having one carbon group attached to nitrogen, represented as RNH2 or ArNH2.
Secondary amine: An amine having two carbon groups attached to nitrogen, represented as R2NH.
Tertiary amine: An amine having three carbon groups attached to nitrogen, represented as R3N.
Aniline: Aromatic primary amine, C6H5NH2, in which -NH2 is directly attached to a benzene ring.
Diazonium salt: A salt containing the diazonium group -N2+ X-, commonly formed by treating aromatic primary amines with NaNO2 and HCl at 273-278 K.
Basicity: The tendency of an amine to accept a proton using the lone pair on nitrogen; stronger bases have lower pKb values.
Carbylamine reaction: A test in which primary amines react with chloroform and alcoholic KOH to form foul-smelling isocyanides.
Hoffmann bromamide degradation: Conversion of an amide into a primary amine having one carbon atom less using Br2 and KOH.

Core concept: why amines are basic

Amines are basic because nitrogen has a lone pair of electrons that can accept a proton to form an ammonium ion. The strength of an amine as a base is not decided by one factor only. In aliphatic amines, alkyl groups show a +I effect and push electron density towards nitrogen, making the lone pair more available. However, in water, the stability of the protonated ion also depends on solvation. Smaller and less hindered ammonium ions are better solvated, so aqueous basicity order may differ from gaseous order. In aromatic amines like aniline, the nitrogen lone pair participates in resonance with the benzene ring, so it is less available for protonation. This is why aniline is much less basic than methylamine. Electron-donating groups on the benzene ring generally increase basicity of aryl amines, while electron-withdrawing groups decrease it. For exams, always mention the correct cause: resonance for weak basicity of aniline, solvation plus +I effect for aqueous order of aliphatic amines.

Classification and naming snapshot

Main methods of preparation: reagent-to-product map

Basicity orders: must not mix conditions

Aspect	Details

Distinguishing tests for amines

Aspect	Details

Aniline and diazonium salts: high-yield revision

Aniline is more reactive than benzene towards electrophilic substitution because -NH2 is a strongly activating ortho-para directing group. With bromine water, it forms white precipitate of 2,4,6-tribromoaniline. For controlled monosubstitution, the -NH2 group is first protected by acetylation to form acetanilide; this reduces activation and mainly gives para product. During nitration, strongly acidic medium converts aniline to the anilinium ion, which is meta directing, so a mixture of o-, p- and m-nitroaniline may form. Aromatic primary amines form benzene diazonium chloride on diazotization with NaNO2 and HCl at 273-278 K. Diazonium salts are extremely useful because -N2+ can be replaced by Cl, Br, I, CN, F, OH or H, and can also undergo coupling reactions with phenols or anilines to form coloured azo dyes.

Diazonium salt reaction sequence

Short worked mini-examples

Predict the product: CH3CONH2 reacts with Br2/KOH. Hoffmann bromamide degradation occurs. CH3CONH2 gives CH3NH2. The product has one carbon less than the amide.
Arrange in increasing basic strength: aniline, ammonia, ethylamine. Aniline < NH3 < ethylamine. Aniline is weakest due to resonance; ethylamine is strongest due to +I effect of ethyl group.
How will you convert aniline to chlorobenzene? First diazotize aniline with NaNO2/HCl at 273-278 K to form benzene diazonium chloride. Then use CuCl/HCl to replace -N2+Cl- by Cl through Sandmeyer reaction.

Board traps and marking cues

Always write 273-278 K for diazotization of aniline; diazonium salts decompose at higher temperature.
Do not write Gabriel phthalimide synthesis for aromatic primary amines; aryl halides do not undergo the required SN2 reaction.
In Hoffmann bromamide degradation, count carbons: amide carbonyl carbon is lost, so product has one carbon less.
Carbylamine test proves primary amine, not only aniline. Both aliphatic and aromatic primary amines give the test.
For aniline bromination, direct bromine water gives 2,4,6-tribromoaniline. To get p-bromoaniline as major product, first protect -NH2 by acetylation.
While comparing basicity, mention the medium. Aqueous order is influenced by solvation; gaseous order mainly follows +I effect.

Must remember equations

RNO2 + 6[H] -> RNH2 + 2H2O
RX + NH3 -> RNH2 + HX, but excess NH3 is used to reduce further alkylation.
RCN + 4[H] -> RCH2NH2
RCONH2 + 4[H] -> RCH2NH2 + H2O
RCONH2 + Br2 + 4KOH -> RNH2 + K2CO3 + 2KBr + 2H2O
RNH2 + CHCl3 + 3KOH -> RNC + 3KCl + 3H2O
C6H5NH2 + NaNO2 + 2HCl -> C6H5N2+Cl- + NaCl + 2H2O
C6H5N2+Cl- + CuCl/HCl -> C6H5Cl + N2
C6H5N2+Cl- + H2O on warming -> C6H5OH + N2 + HCl

Quick revision checks

Q: Why is aniline less basic than methylamine? A: In aniline, nitrogen lone pair is delocalised into the benzene ring by resonance, so it is less available for protonation.
Q: Which reagent converts benzamide to aniline with one carbon less? A: Br2/KOH; Hoffmann bromamide degradation converts C6H5CONH2 to C6H5NH2.
Q: Which amines give the carbylamine test? A: Only primary amines, both aliphatic and aromatic.
Q: What is the temperature range for diazotization of aniline? A: 273-278 K using NaNO2 and HCl.

Frequently Asked Questions

What is the most important part of Amines for CBSE Class 12?

Focus on preparation methods, basicity order, chemical tests, aniline reactions and diazonium salts. Conversions involving aniline and benzene diazonium chloride are especially common in board-style questions.

Why are aliphatic amines generally stronger bases than ammonia?

Alkyl groups show +I effect and increase electron density on nitrogen, making the lone pair more available for protonation. In water, solvation also affects the exact order.

Why is aniline weakly basic?

The lone pair on nitrogen in aniline is delocalised into the benzene ring by resonance. Since the lone pair is less available to accept H+, aniline is weaker base than aliphatic amines and ammonia.

What is the difference between Gabriel synthesis and Hoffmann bromamide reaction?

Gabriel phthalimide synthesis prepares pure primary aliphatic amines from alkyl halides. Hoffmann bromamide degradation converts an amide into a primary amine with one carbon atom less.

How should I revise Amines quickly before an exam?

Memorise the named reactions, diazonium salt conversions, and basicity orders first. Then practise 4-5 conversions using YoLearn flashcards or quizzes to check reagents, conditions and products.