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Full Organic Chemistry Short Notes (Part 3) – Amines & Polymers | Class 12 & JEE 2026


🔖Organic Chemistry Shorts Notes (Part - 3) |Class 12 & JEE 2026

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Amines are derivatives of ammonia (NH₃), where one or more hydrogen atoms are replaced by alkyl or aryl groups. They are important because they form the basis of dyes, dr#gs, polymers, agrochemicals, and several organic syntheses.

This chapter contains preparation, physical & chemical properties, reduction pathways, acylation, alkylation, diazonium salt chemistry, and tests 


Polymers are extremely important materials in our daily lives — from plastics to fibres, rubbers, and even the proteins inside our body. This chapter covers the basics of polymer science, types of polymers, classification, and important commercial polymers.


✅ SECTION 1 - AMINES


🔵 1. Classification of Amines

Amines are classified as:

  • Primary amine (1°): R–NH₂

  • Secondary amine (2°): R₂NH

  • Tertiary amine (3°): R₃N

Aromatic amines have the –NH₂ group attached to a benzene ring (e.g., aniline).

🔵 2. Methods of Preparation of Amines

⭐ A. Ammonolysis of Alkyl Halides

R–X + NH₃ (excess) → R–NH₂
By-product: HX

This reaction also forms:

  • Secondary amines

  • Tertiary amines

  • Quaternary ammonium salts

⭐ B. Reduction of Nitro Compounds

Nitro compound → Amine
Reagents :

  • Sn/HCl

  • Fe/HCl

  • H₂/Pd

  • SnCl₂ + HCl

Example:
NO₂ → NH₂

⭐ C. Gabriel Phthalimide Synthesis

This method prepares pure primary amines.

Steps:

  1. Phthalimide + alcoholic KOH → potassium phthalimide

    • Alkyl halide → N-alkylphthalimide

  3. Hydrolysis → primary amine

This avoids formation of secondary/tertiary amines.

⭐ D. Hoffmann Bromamide Degradation

Amide → 1° amine (with one carbon less)
Reagents: Br₂ + KOH

Reaction:
R–CONH₂ → R–NH₂

This leads to loss of one carbon atom.

⭐ E. Reduction of Nitriles

R–C≡N → R–CH₂–NH₂
Reagents in PDF:

  • LiAlH₄ / ether

  • Na/ethanol

  • H₂/Ni

⭐ F. Reduction of Amides

Amides → Amines
Reagent: LiAlH₄

⭐ G. Reduction of Oximes

Oxime → Primary amine
Reagents:

  • Na(Hg)/EtOH

  • H₂/Ni

🔵 3. Reactions of Amines 

⭐ A. Alkylation

R–NH₂ + RX → R–NH–R' → R₂NH → R₃N → R₄N⁺
Occurs stepwise until quaternary salt forms.

⭐ B. Acylation

Reagent: Acyl chloride (CH₃COCl)
Produces amide:

R–NH₂ + CH₃COCl → R–NHCOCH₃

This reaction tests for primary and secondary amines.

⭐ C. Carbylamine Reaction (Test for Primary Amines)

Reagent: CHCl₃ + KOH
Product: Foul-smelling isocyanide

Only primary aliphatic/aromatic amines give positive test.

⭐ D. Reaction with HNO₂ (Nitrous Acid)

For 1° aliphatic amines

→ Alcohol + N₂ gas

For 1° aromatic amines

→ Diazonium salts

⭐ E. Reaction with HCl (Salt Formation)

R–NH₂ + HCl → R–NH₃⁺Cl⁻

Amines behave as bases.

🔵 4. Electrophilic Substitution in Aromatic Amines

 Effect of –NH₂ group on benzene.

–NH₂ is strongly activating and ortho/para directing.

This leads to:

  • o- and p- nitroaniline

  • o- and p- halogen substitution

  • sulphonation

🔵 5. Protection of Amino Group

Acetylation using (CH₃CO)₂O → Acetanilide
Protects –NH₂ from strong reactions

Used in nitration:

Aniline → Acetanilide → Nitration → Nitroacetanilide → Hydrolysis → p-nitroaniline

🔵 6. Diazotisation and Diazotisation Reactions

(One of the most important parts of the chapter)

⭐ A. Formation of Benzene Diazonium Salt

Aniline + NaNO₂ + HCl (0–5°C) → Benzene diazonium chloride

This compound is key for making many aromatic derivatives.

⭐ B. Reactions of Diazotised Amines (Arenediazonium Salts)

 All major reactions:

⭐ 1. Sandmeyer Reactions

Replace –N₂⁺Cl⁻ with:

Reagent Product
CuCl/HCl Aryl chloride
CuBr/HBr Aryl bromide
CuCN/KCN Aryl cyanide

⭐ 2. Gattermann Reaction

Arenediazonium salt + Cu/HCl → Ar–Cl
or Cu/HBr → Ar–Br

⭐ 3. Replacement with Iodine

KI → Ar–I

⭐ 4. Replacement with Fluorine

Using HBF₄ (Fluoroboration) → Ar–F

⭐ 5. Hydrolysis

H₂O + heat → Phenol (Ar–OH)

⭐ 6. Reduction

Sn/HCl or H₃PO₂ → Aniline (Ar–NH₂)

⭐ 7. Coupling Reaction (Azo Dye Formation)

One of the most colorful reactions.

Arenediazonium salt + phenol/aniline → Azo dye
(Orange, red, yellow dyes)

Occurs through electrophilic substitution.

🔵 7. Hoffmann Bromamide Degradation

Used to convert:

R–CONH₂ → R–NH₂
Reagents: Br₂ + KOH
One carbon is removed.

🔵 8. Summary of Important Reactions

Here is a clean, exam-ready summary :

  • Alkyl halide + NH₃ → amine (ammonolysis)

  • Nitro → amine (Sn/HCl, Fe/HCl, H₂/Pd)

  • Gabriel synthesis → pure 1° amines

  • Hoffmann bromamide → 1° amine (1 carbon less)

  • Nitrile → amine (LiAlH₄ or H₂/Ni)

  • Carbylamine test → only 1° amines

  • Acylation → amide formation

  • Diazotisation → diazonium salt (0–5°C)

  • Sandmeyer → Ar–Cl, Ar–Br, Ar–CN

  • Gattermann → Ar–Cl / Ar–Br

  • Coupling → azo dyes


✅ SECTION 2 - POLYMERS

🔵 1. What Are Polymers?

Polymers are high molecular mass macromolecules formed by repeating simple units called monomers.

The reaction in which small molecules (monomers) join to form a large molecule (polymer) is called polymerisation.

Examples:

  • Polythene

  • PVC

  • Nylon

  • Natural rubber

  • Starch

🔵 2. Types of Polymers 

⭐ A. Natural Polymers

These occur naturally in plants or animals.

Examples:

  • Starch

  • Cellulose

  • Proteins

  • Natural rubber

⭐ B. Synthetic Polymers (Man-made Polymers)

Made artificially in laboratories or industries.

Examples:

  • Polythene

  • PVC

  • Nylon-6,6

  • Teflon

  • Orlon (acrylic fibre)

⭐ C. Semi-Synthetic Polymers

Modified natural polymers.

Examples:

  • Rayon (cellulose acetate)

  • Vulcanised rubber

🔵 3. Classifications Based on Structure

⭐ A. Linear Polymers

Long, straight chains with no branching.

Examples:

  • High Density Polythene (HDPE)

  • Nylon

  • Polyesters

⭐ B. Branched Chain Polymers

Main chain + side chains branching out.

Examples:

  • Low Density Polythene (LDPE)

  • Starch

  • Glycogen

⭐ C. Cross-Linked (Network) Polymers

Formed from bi-functional or tri-functional monomers; rigid, hard.

Examples:

  • Bakelite

  • Melamine-formaldehyde resin

  • Glyptal resin

🔵 4. Types Based on Mode of Polymerisation

⭐ A. Addition Polymers

Formed by polymerising unsaturated monomers (C=C or C≡C).

Examples:

  • Polythene

  • PVC

  • Buna-S

  • Orlon

⭐ B. Condensation Polymers

Formed by combining monomers with elimination of small molecules like H₂O, HCl, or alcohol.

Examples:

  • Nylon-6,6

  • Dacron

  • Bakelite

🔵 5. Classification Based on Intermolecular Forces

⭐ A. Elastomers

Rubber-like materials with very weak intermolecular forces.

Examples:

  • Natural rubber

  • Buna-S

  • Buna-N

⭐ B. Fibres

Thread-like polymers that can be woven into fabrics.

Examples:

  • Nylon-6,6

  • Terylene

  • Polyacrylonitrile (PAN)

⭐ C. Thermoplastics

Linear polymers that soften on heating and harden on cooling.

Examples:

  • Polythene

  • Polystyrene

Plasticizers :
High-boiling esters or haloalkanes are added to plastics to make them soft.

⭐ D. Thermosetting Plastics

Soft initially, but become hard upon heating and cannot be remelted.

Examples:

  • Bakelite

  • Melamine resin

  • Urea-formaldehyde resin

🔵 6. Mechanisms of Polymerisation

⭐ A. Free Radical Polymerisation

Used for monosubstituted alkenes.
Examples: polythene, polystyrene.

⭐ B. Cationic Polymerisation

Involves formation of a carbocation.
Used for electron-rich alkenes.

⭐ C. Anionic Polymerisation

Involves formation of a carbanion.
Used for electron-deficient alkenes.

🔵 7. Important Polymer Families

⭐ A. Polyamides

Contain –CONH– (amide) linkage.

Examples:

  • Nylon-6,6

  • Nylon-6

⭐ B. Polyesters

Contain –COO– (ester) linkage.

Example:

  • Dacron

⭐ C. Natural Rubber

A linear polymer of 1,4-polyisoprene.

Vulcanisation:
Heating natural rubber with sulphur at 110°C introduces S–S cross-links, improving elasticity.

⭐ D. Biopolymers

Natural biological polymers:

  • Proteins

  • Nucleic acids

  • Polysaccharides

⭐ E. Biodegradable Polymers

Can be degraded by microorganisms.

 example:

  • Aliphatic polyesters

🔵 8. Important Polymers 


Polymer Name Composition Use
Saran Copolymer of vinylidene chloride + vinyl chloride Food-wrapping material
ABS Rubber Acrylonitrile + buta-1,3-diene + styrene Hard plastics, helmets
Buna-S Styrene + butadiene Bubble gum, rubber products
Dynel Vinyl chloride + acrylonitrile Human hair wigs
Silk Natural polyamide Fabrics, textile
Thermocol Foamed polystyrene Packaging

🔵 9. Revision Points 

  • Polymers = high molecular mass molecules.

  • Natural → starch, cellulose; Synthetic → PVC, nylon.

  • Linear polymers → HDPE; Branched → LDPE.

  • Cross-linked polymers → Bakelite.

  • Addition polymer → polythene.

  • Condensation polymer → nylon-6,6.

  • Elastomers → natural rubber, Buna-S.

  • Fibres → nylon, PAN.

  • Thermoplastics → polythene.

  • Thermosetting → Bakelite, melamine.

  • Natural rubber = polymer of isoprene.

  • Vulcanisation → S–S crosslinking at 110°C.

  • Biopolymers = proteins, nucleic acids.

  • Biodegradable polymer → aliphatic polyesters.


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