13.7.9 Functional Groups Containing Carbon, Hydrogen and Nitrogen: Amines

This topic explains amines — organic compounds containing the amino group (–NH₂).

Definition

The functional group of amines is –NH₂.

Simple explanation: An amine is an organic compound with an –NH₂ group.

Main Idea

• Functional group: –NH₂ (amino group)
• General formula: R–NH₂
• Amines are derivatives of ammonia (NH₃), where one or more hydrogen atoms are replaced by alkyl groups.

Simple explanation: Amines are like ammonia, but with carbon groups attached to the nitrogen.

Core Concept

The Amino Group

–NH₂

• A nitrogen atom attached to two hydrogen atoms and one alkyl group.
• This is the functional group of amines.

Simple explanation: The –NH₂ group is the "signature" of an amine.

General Formula

R–NH₂

• **R** = alkyl group
• **–NH₂** = amino group

Simple explanation: R–NH₂ is the general formula for primary amines.

Examples from the Book

Simple explanation: Methyl amine is the simplest amine; ethyl amine has a two-carbon chain.

Detailed Explanation

What Makes a Compound an Amine?

• A nitrogen atom.
• The nitrogen is bonded to carbon (alkyl group) and hydrogen.
• The general structure R–NH₂ (for primary amines).

Examples:

Simple explanation: If nitrogen is attached to a carbon group and hydrogens, it's an amine.

Types of Amines

Amines are classified based on how many hydrogen atoms of ammonia are replaced by alkyl groups:

Simple explanation: Primary = 1 alkyl group; secondary = 2; tertiary = 3.

Naming Amines

• The alkyl group name.
• Adding the word "amine" at the end.

Examples:

Simple explanation: Name the alkyl group(s), then add "amine."

Physical Properties of Amines

Simple explanation: Amines have a characteristic fishy smell and lower boiling points than alcohols.

Why Amines Have a Fishy Smell

• Small amines (like methyl amine and ethyl amine) have a strong, fishy odour.
• This is due to the nitrogen atom with its lone pair of electrons.
• The smell of rotting fish is due to amines produced by bacterial decomposition.

Simple explanation: The fishy smell of amines is why spoiled fish smells bad.

Chemical Properties of Amines

Amines are weak bases — they can accept protons (H⁺).

1. Reaction with water (basic): CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH^-

2. Reaction with acids (salt formation): CH₃NH₂ + HCl → CH₃NH₃⁺Cl^-

3. Reaction with carboxylic acids (amide formation): CH₃NH₂ + CH₃COOH → CH₃CONHCH₃ + H₂O

Simple explanation: Amines are weak bases — they react with acids to form salts.

Why Amines Are Basic

• The nitrogen atom in an amine has a lone pair of electrons.
• This lone pair can accept a proton (H⁺).
• So amines act as bases (proton acceptors).
• This is why amines turn red litmus blue and react with acids.

Simple explanation: The lone pair on nitrogen lets amines accept protons — making them basic.

Uses of Amines

Simple explanation: Amines are used in medicines, dyes, pesticides, and many other products.

Amines in Nature

• Amino acids — the building blocks of proteins — contain both an amino group (–NH₂) and a carboxyl group (–COOH).
• Neurotransmitters (like dopamine, serotonin) are amines.
• Alkaloids (like nicotine, caffeine) are amines.
• DNA and RNA bases contain amino groups.

Simple explanation: Amines are important in biology — they are found in proteins, neurotransmitters, and DNA.

Intermediate Level

Structure of Amines

• A nitrogen atom is bonded to:
• Two hydrogen atoms
• One alkyl group (R)

Structure:

R–NH₂

Simple explanation: Nitrogen is attached to a carbon group and two hydrogens.

Types of Amines — In Detail

Simple explanation: The type depends on how many alkyl groups are attached to nitrogen.

Physical Properties

Chemical Properties

Why Amines Are Basic

• Nitrogen has a lone pair of electrons.
• This lone pair can accept a proton (H⁺).
• So amines are proton acceptors (Bronsted-Lowry bases).
• This makes them basic — they turn red litmus blue.

Simple explanation: The lone pair on nitrogen makes amines basic.

Comparison with Other Organic Compounds

Simple explanation: Amines are basic; amides and alcohols are neutral.

Uses of Amines in Detail

Amines in Biology

• Amino acids: contain –NH₂ and –COOH; building blocks of proteins.
• Neurotransmitters: dopamine, serotonin — amines that transmit nerve signals.
• Alkaloids: nicotine, caffeine — natural amines from plants.
• DNA/RNA bases: contain amino groups.

Simple explanation: Amines are essential for life — they are in proteins, nerves, and DNA.

Important Points

• - Amines: organic compounds containing the –NH₂ group (amino group).
• - Functional group: –NH₂.
• - General formula: R–NH₂ (for primary amines).
• - Examples:
• - Methyl amine: CH₃NH₂
• - Ethyl amine: C₂H₅NH₂
• - Types: primary (R–NH₂), secondary (R₂NH), tertiary (R₃N).
• - Naming: alkyl group + "amine" (e.g., methyl amine).
• - Physical properties: fishy smell; lower boiling points than alcohols; soluble in water (small amines).
• - Chemical properties: weak bases — accept protons; react with acids to form salts; react with carboxylic acids to form amides.
• - Uses: pharmaceuticals, pesticides, dyes, rubber chemicals, surfactants.
• - In nature: amino acids, neurotransmitters, alkaloids, DNA/RNA bases.

Remember

• - **Amine** = **–NH₂** group.
• - General formula: R–NH₂.
• - Naming: alkyl + amine (e.g., methyl amine).
• - Examples:
• - Methyl amine: CH₃NH₂
• - Ethyl amine: C₂H₅NH₂
• - Smell: fishy.
• - Basic — accepts protons.
• - Types: primary, secondary, tertiary.
• - Uses: medicines, dyes, pesticides.
• - In nature: amino acids, neurotransmitters, DNA.

Common Mistakes

• 1. Confusing amines with amides. Amines have –NH₂; amides have –CO–NH₂.
• 2. Thinking amines are neutral. Amines are basic — they accept protons.
• 3. Forgetting the fishy smell. Small amines have a fishy odour.
• 4. Confusing primary, secondary, and tertiary amines. Primary = 1 alkyl group; secondary = 2; tertiary = 3.
• 5. Thinking all amines are gases. Small amines are gases; larger amines are liquids or solids.
• 6. Forgetting the importance of amines in biology. Amino acids, neurotransmitters, and DNA bases are amines.

Quick Revision

• Amines: organic compounds containing the –NH₂ group (amino group).
• Functional group: –NH₂.
• General formula: R–NH₂ (for primary amines).
• Examples:
• Methyl amine: CH₃–NH₂
• Ethyl amine: CH₃CH₂–NH₂
• Types:
• Primary amine: R–NH₂
• Secondary amine: R₂–NH
• Tertiary amine: R₃–N
• Naming: alkyl group + "amine" (e.g., methyl amine, ethyl amine).
• Physical properties: fishy smell; lower boiling points than alcohols; soluble in water (small amines).
• Chemical properties: weak bases — accept protons; react with acids to form salts; react with carboxylic acids to form amides.
• Uses: pharmaceuticals, pesticides, dyes, rubber chemicals, surfactants.
• In nature: amino acids, neurotransmitters, alkaloids, DNA/RNA bases.

60-Second Revision

• **Amine** = **–NH₂** group.
• General formula: R–NH₂.
• Examples: CH₃NH₂ (methyl amine), C₂H₅NH₂ (ethyl amine).
• Smell: fishy.
• Basic — accepts protons.
• Warning: amines have –NH₂; amides have –CO–NH₂ — don't confuse them.