13.7.8 Amides

This topic explains amides — organic compounds containing the amide group (–CO–NH₂).

Definition

Compounds having the general formula R–CO–NH₂ are called amides.

Where: - R is an alkyl group.

Simple explanation: An amide is an organic compound with a –CO–NH₂ group.

Main Idea

• Functional group: –CO–NH₂ (amide group)
• General formula: R–CO–NH₂
• Amides are derivatives of carboxylic acids — the –OH of the carboxyl group is replaced by –NH₂.

Simple explanation: Amides are like carboxylic acids, but with an –NH₂ group instead of –OH.

Core Concept

The Amide Group

–CO–NH₂

• A carbonyl group (C=O) attached to an –NH₂ group.
• This is the functional group of amides.

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

General Formula

R–CO–NH₂

• **R** = alkyl group (or H)
• **–CO–NH₂** = amide group

Simple explanation: R–CO–NH₂ is the general formula for amides.

Example from the Book

Simple explanation: Ethanamide is the simplest amide with an alkyl group (CH₃).

Detailed Explanation

What Makes a Compound an Amide?

• A **carbonyl group (C=O)**.
• An –NH₂ group attached to the carbonyl carbon.

Examples:

Simple explanation: If it has –CO–NH₂, it's an amide.

How Amides Are Formed

Amides are formed from carboxylic acids by replacing the –OH group with an –NH₂ group.

General reaction:

Carboxylic acid + Ammonia → Amide + Water

Example:

CH₃COOH + NH₃ → CH₃CONH₂ + H₂O

- Acetic acid + Ammonia → Ethanamide + Water

Simple explanation: Acid + Ammonia → Amide + Water.

Naming Amides

• The alkane name (with -e changed to -amide).
• No separate prefix for the –NH₂ group.

Examples:

Simple explanation: Amides end in -amide.

Physical Properties of Amides

Simple explanation: Amides have high boiling points because they form hydrogen bonds.

Why Amides Have High Boiling Points

• The –NH₂ group can form hydrogen bonds with the C=O group of another amide molecule.
• These hydrogen bonds are strong.
• So a lot of energy is needed to break them.
• This gives amides high boiling points.

Simple explanation: Hydrogen bonding makes amides hard to boil.

Chemical Properties of Amides

1. Hydrolysis (acidic): CH₃CONH₂ + H₂O H⁺→ CH₃COOH + NH₃

2. Hydrolysis (basic): CH₃CONH₂ + NaOH → CH₃COONa + NH₃

3. Dehydration: CH₃CONH₂ P₂O₅→ CH₃CN + H₂O (Amide → Nitrile)

Simple explanation: Amides can be hydrolyzed (broken down by water) or dehydrated (lose water).

Uses of Amides

Simple explanation: Amides are used in fertilizers, plastics, textiles, medicines, and are the building blocks of proteins.

Amides in Nature — Proteins

• Proteins are natural polyamides.
• The peptide bond in proteins is an amide bond.
• Amino acids are linked by amide (peptide) bonds to form proteins.

Simple explanation: The bonds that hold proteins together are amide bonds.

Intermediate Level

Structure of Amides

• A carbonyl group (C=O) is attached to an –NH₂ group.
• The carbonyl carbon may also be attached to R (H or alkyl).

Structure:

R–C(=O)–NH₂

Simple explanation: Amides have a –CO–NH₂ group at the end of a carbon chain.

Formation of Amides

From carboxylic acids:

R–COOH + NH₃ → R–CONH₂ + H₂O

Example:

CH₃COOH + NH₃ → CH₃CONH₂ + H₂O

Simple explanation: Replace the –OH of a carboxylic acid with –NH₂ to get an amide.

Naming Amides

Simple explanation: Amides end in -amide.

Physical Properties

Chemical Properties

Amides in Nature

• Proteins are natural polyamides.
• The peptide bond is an amide bond.
• Amino acids are linked by amide bonds to form proteins.

Simple explanation: The bonds that hold proteins together are amide bonds.

Uses of Amides

Important Points

• - Amides: compounds with the general formula R–CO–NH₂.
• - Functional group: –CO–NH₂ (amide group).
• - General formula: R–CO–NH₂ (where R is an alkyl group).
• - Example: Ethanamide: CH₃–CO–NH₂.
• - Formation: carboxylic acid + ammonia → amide + water.
• - Naming: ends in -amide (e.g., methanamide, ethanamide).
• - Physical properties: high boiling points (hydrogen bonding); soluble in water (small amides); solids.
• - Chemical properties: hydrolysis (acidic/basic); dehydration to nitriles.
• - Uses: fertilizers, plastics (nylon, Kevlar), medicines, proteins.

Remember

• - **Amide** = **–CO–NH₂** group.
• - General formula: R–CO–NH₂.
• - Naming: ends in -amide.
• - Example: Ethanamide: CH₃CONH₂.
• - Formed from: carboxylic acid + ammonia.
• - High boiling point (hydrogen bonding).
• - Uses: fertilizers, plastics, medicines, proteins.

Common Mistakes

• 1. Confusing amides with amines. Amines have –NH₂ (no C=O); amides have –CO–NH₂.
• 2. Confusing amides with carboxylic acids. Carboxylic acids have –COOH; amides have –CO–NH₂.
• 3. Forgetting the formation reaction. Carboxylic acid + ammonia → amide + water.
• 4. Confusing the naming. Amides end in -amide (e.g., ethanamide).
• 5. Thinking amides are gases. Most amides are solids at room temperature.
• 6. Forgetting the importance of amides in proteins. Proteins are natural polyamides — peptide bonds are amide bonds.

Quick Revision

• Amides: compounds having the general formula R–CO–NH₂ (where R is an alkyl group).
• Functional group: –CO–NH₂ (amide group).
• **Example:** Ethanamide: CH₃–C(=O)–NH₂
• Formation: carboxylic acid + ammonia → amide + water.
• CH₃COOH + NH₃ → CH₃CONH₂ + H₂O
• Naming: ends in -amide (e.g., methanamide, ethanamide).
• Physical properties: high boiling points due to hydrogen bonding; soluble in water (small amides); solids at room temperature.
• Chemical properties: hydrolysis (acidic/basic); dehydration to nitriles.
• Uses: fertilizers (urea), plastics (nylon, Kevlar), medicines, and as the building blocks of proteins (peptide bonds are amide bonds).

60-Second Revision

• **Amide** = **–CO–NH₂** group.
• General formula: R–CO–NH₂.
• Example: Ethanamide: CH₃CONH₂.
• Formed from: carboxylic acid + ammonia.
• High boiling point (hydrogen bonding).
• Warning: amides have –CO–NH₂; amines have –NH₂ — don't confuse them.