Amines Class 12 Notes PDF | Complete NCERT Guide, Reactions & PYQs

01
Introduction to Amines Class 12 Notes PDF

Amines are organic derivatives of ammonia (NH₃) produced by replacing one or more hydrogen atoms with alkyl or aryl groups. This amines class 12 notes pdf guide provides a deep dive into these nitrogen-containing compounds, which are fundamental to biology and industry. Amines play a crucial role in the structure of proteins, vitamins, and hormones, making them a high-yield chapter for NEET aspirants. Understanding the basicity and reactive nature of amines is essential for scoring well in the organic chemistry section of the competitive entrance examination.

Functional groups of amines are defined by the number of carbon atoms directly attached to the nitrogen. Whether you are dealing with primary aliphatic amines or complex aromatic derivatives like aniline, the electronic effects of the nitrogen lone pair dictate the molecule’s chemical personality. In this study guide, we will explore the synthesis, properties, and significant named reactions that you must master for a top NEET rank.

02
Structure and Geometry of Amines

The nitrogen atom in amines is sp³ hybridized. However, unlike the tetrahedral geometry of carbon, amines adopt a Trigonal Pyramidal shape. This is due to the presence of a lone pair of electrons on the nitrogen atom, which exerts more repulsion than bonding pairs, squeezing the bond angles.

BOND ANGLES In trimethylamine, the C−N−C bond angle is approximately 108°, slightly less than the ideal tetrahedral angle of 109.5°.

HYBRIDIZATION Nitrogen uses four sp³ orbitals: three for bonding with H or C, and one for the lone pair.

03
Classification for Amines Class 12 Notes PDF

Classification is based on the number of organic groups attached to the nitrogen atom. This is a foundational concept in the amines class 12 notes pdf that prevents confusion during naming and mechanism prediction.

Type	General Formula	Example	Description
Primary (1°)	R−NH₂	Ethylamine	One hydrogen replaced by an alkyl/aryl group.
Secondary (2°)	R₂NH	Dimethylamine	Two hydrogens replaced.
Tertiary (3°)	R₃N	Triethylamine	All three hydrogens replaced.

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04
Preparation Methods in Amines Class 12 Notes PDF

Synthesis reactions for amines are frequent NEET targets. The amines class 12 notes pdf typically highlights three major named reactions that offer high-purity products or involve interesting carbon-chain shifts.

HOFFMANN BROMAMIDE DEGRADATION

R−CONH₂ + Br₂ + 4NaOH → R−NH₂ + Na₂CO₃ + 2NaBr + 2H₂O

(Note: The amine formed has one carbon atom less than the parent amide.)

Key Synthesis Routes

Gabriel Phthalimide Synthesis: Used exclusively for preparing pure 1° aliphatic amines. Aromatic amines cannot be prepared this way due to the low reactivity of aryl halides in nucleophilic substitution.
Reduction of Nitriles: R−CN reduced by LiAlH₄ or catalytic hydrogenation yields 1° amines.
Ammonolysis of Alkyl Halides: Reaction of R−X with ethanolic ammonia. It often results in a mixture of 1°, 2°, 3° amines and quaternary salts.

TIP

To obtain a primary amine as the major product during ammonolysis, always use a large excess of Ammonia (NH₃).

05
Physical Properties: Boiling Point & Solubility

Primary and secondary amines can form intermolecular hydrogen bonds due to the presence of N−H bonds. Tertiary amines lack these bonds between themselves, affecting their physical state and boiling points.

Boiling Point Order: 1° Amines > 2° Amines > 3° Amines (for isomeric amines).

Low molecular weight amines are soluble in water because they can form H-bonds with water molecules. However, solubility decreases as the size of the hydrophobic alkyl group increases.

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Chemical Properties for Amines Class 12 Notes PDF

The reactivity of amines is primarily due to the lone pair of electrons on the nitrogen atom. This makes them act as both Lewis Bases and nucleophiles. Understanding basicity is the most critical part of this amines class 12 notes pdf.

Basicity of Amines

Basicity depends on the ease with which the nitrogen lone pair can be donated. In the gas phase, the order is straightforward: 3° > 2° > 1° > NH₃ due to the +I effect of alkyl groups. However, in aqueous solutions, the order becomes complex due to **Solvation Effects** and **Steric Hindrance**.

Alkyl Group	Basicity Order (Aqueous Phase)
Methyl (−CH₃)	2° > 1° > 3° > NH₃
Ethyl (−C₂H₅)	2° > 3° > 1° > NH₃

WARN

Aromatic amines (Aniline) are much weaker bases than ammonia. This is because the nitrogen lone pair is delocalized into the benzene ring by resonance, making it less available for protonation.

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07
Important Chemical Reactions: Carbylamine & Nitrous Acid

Two reactions are quintessential for distinguishing different classes of amines in the lab and on the NEET exam paper.

CARBYLAMINE TEST Only 1° amines react with CHCl₃ and alc. KOH to form isocyanides (carbylamines) with an extremely foul smell.

HINSBERG TEST Reaction with Benzenesulfonyl chloride. 1° amine products are soluble in alkali; 2° are insoluble; 3° do not react.

Reaction with Nitrous Acid (HNO₂)

This is a very important distinguishing test discussed in every amines class 12 notes pdf guide:

Primary Aliphatic: Form Alcohols and evolve N₂ gas quantitatively.
Primary Aromatic: Form stable **Diazonium Salts** at 0−5°C.
Secondary: Form yellow oily N-nitrosamines.
Tertiary: Form soluble nitrite salts.

08
Diazonium Salts: A Versatile Intermediate

Aryl diazonium salts (Ar−N₂⁺X⁻) are invaluable for preparing variety of aromatic compounds that cannot be made by direct substitution. They are prepared by the **Diazotization** of aniline.

SANDMEYER REACTION

Ar−N₂Cl + Cu₂Cl₂/HCl → Ar−Cl + N₂

Coupling Reactions

Diazonium salts react with phenols and aromatic amines to form highly colored **Azo compounds** used as dyes. Example: Benzene diazonium chloride + Phenol → p-Hydroxyazobenzene (Orange dye).

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Quick Revision Sheet

Geometry: Trigonal pyramidal; sp³ hybridized nitrogen.
Basicity order: 2° > 3° > 1° (Ethyl) and 2° > 1° > 3° (Methyl) in water.
Gabriel Synthesis: Only for aliphatic 1° amines.
Hoffmann Bromamide: Decreases chain length by one carbon atom.
Carbylamine test: Distinguishes 1° amines (foul smell).
Aniline: Ortho-para directing; reacts with Br₂ water to give 2,4,6-tribromoaniline (white ppt).
Acetylation: Used to protect the −NH₂ group in aniline to prevent oxidation or uncontrolled substitution.
Diazotization: Done at ice-cold temperature (0−5°C).
Sandmeyer vs Gattermann: Sandmeyer uses copper salts; Gattermann uses copper powder.
Isocyanide: Functional isomer of nitrile.

Download Amines Formula Sheet

09
Frequently Asked Questions

Why is Gabriel Phthalimide synthesis not used for preparing Aniline?

Gabriel synthesis involves nucleophilic substitution (S_N2) of an alkyl halide by the phthalimide anion. Aryl halides (like chlorobenzene) do not undergo nucleophilic substitution under normal conditions due to resonance and partial double bond character of the C-X bond, making them unsuitable for this method.

Why are amines less acidic than alcohols of comparable mass?

Oxygen is more electronegative than Nitrogen. Therefore, the O−H bond is more polar than the N−H bond, making it easier to release a proton. Additionally, the alkoxide ion (RO⁻) is more stable than the amide ion (RNH⁻) because the negative charge is on a more electronegative atom.

Explain why aniline does not undergo Friedel-Crafts reaction.

In a Friedel-Crafts reaction, anhydrous AlCl₃ acts as a Lewis acid catalyst. Aniline is a strong Lewis base. It reacts with AlCl₃ to form a salt. This complexation places a positive charge on the Nitrogen atom, which strongly deactivates the benzene ring, preventing further electrophilic attack.

What is the role of acetylation in aniline nitration?

Direct nitration of aniline using conc. HNO₃/H₂SO₄ oxidizes the sensitive −NH₂ group and produces a high amount of meta-nitroaniline. By converting aniline to acetanilide (acetylation), the activating effect of the amino group is reduced, protecting it from oxidation and directing nitration strictly to the para position.

Why do 3° amines have the lowest boiling point among isomeric amines?

Boiling point depends on the strength of intermolecular forces. 1° and 2° amines have N−H bonds that allow for extensive intermolecular hydrogen bonding. 3° amines have no hydrogen attached to Nitrogen, meaning they cannot form H-bonds with themselves, resulting in much weaker dipole-dipole attractions.

What is the product of the reaction between aniline and bromine water?

Aniline is highly activated. When reacted with bromine water, it undergoes rapid multiple substitution at all available ortho and para positions, resulting in a white precipitate of 2,4,6-tribromoaniline.

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Table of Contents — Chemistry Class 12

Chemistry — Class 12

01	Solutions	Go to page
02	Electrochemistry	Go to page
03	Chemical Kinetics	Go to page
04	d- and f-Block Elements	Go to page
05	Coordination Compounds	Go to page
06	Haloalkanes and Haloarenes	Go to page
07	Alcohols, Phenols and Ethers	Go to page
08	Aldehydes, Ketones and Carboxylic Acids	Go to page
09	Amines	Go to page
10	Biomolecules	Go to page

Amines Class 12 PDF: The Ultimate NEET Preparation Guide

01
Introduction to Amines Class 12 Notes PDF

02
Structure and Geometry of Amines

03
Classification for Amines Class 12 Notes PDF