Chapter 18

Chapter 17: Amines and Amides

Introduction

Amines and amides are important classes of organic compounds containing nitrogen. They play vital roles in biological systems, synthetic chemistry, and industrial applications. This guide covers their structure, nomenclature, physical properties, and key reactions.

Structure and Classification

Types of Amines

• Primary amine: Nitrogen atom bonded to one alkyl or aryl group and two hydrogens. Example: methylamine ($CH_3NH_2$).

• Secondary amine: Nitrogen atom bonded to two alkyl or aryl groups and one hydrogen. Example: dimethylamine ($CH_3NHCH_3$).

• Tertiary amine: Nitrogen atom bonded to three alkyl or aryl groups. Example: trimethylamine ($N(CH_3)_3$).

Types of Amides

• Primary amide: Nitrogen atom bonded to one acyl group and two hydrogens. Example: acetamide ($CH_3CONH_2$).

• Secondary amide: Nitrogen atom bonded to one acyl group, one alkyl/aryl group, and one hydrogen.

• Tertiary amide: Nitrogen atom bonded to one acyl group and two alkyl/aryl groups.

Nomenclature

IUPAC Naming of Amines

• Identify the longest carbon chain attached to the nitrogen.

• Use the suffix -amine for simple amines.

• For secondary and tertiary amines, use N- prefixes to indicate substituents on nitrogen.

• Example: N-ethyl-N-methylpropanamine for a tertiary amine with ethyl and methyl groups on nitrogen.

IUPAC Naming of Amides

• Replace the -oic acid or -ic acid ending of the parent carboxylic acid with -amide.

• Substituents on nitrogen are indicated with N- prefixes.

• Example: N,N-dimethylacetamide ($CH_3CON(CH_3)_2$).

Physical Properties

Boiling Points and Hydrogen Bonding

• Amines can form hydrogen bonds, but less effectively than alcohols due to the lower electronegativity of nitrogen.

• Primary and secondary amines have higher boiling points than tertiary amines due to hydrogen bonding.

• Amides have strong hydrogen bonding, resulting in higher boiling points than amines and comparable to carboxylic acids.

• Example: Boiling point order: Amide > Alcohol > Amine (primary/secondary) > Amine (tertiary).

Solubility

• Amines are generally soluble in water due to hydrogen bonding, especially primary and secondary amines.

• Amides are also water-soluble, particularly simple amides.

Chemical Properties and Reactions

Basicity

• Amines are basic due to the lone pair of electrons on nitrogen, which can accept protons.

• Amides are much less basic than amines because the lone pair on nitrogen is delocalized by resonance with the carbonyl group.

• Example: Reaction with acids: Amines form ammonium salts ($RNH_2 + HCl \rightarrow RNH_3^+Cl^-$).

Reactions of Amines

• Alkylation: Amines react with alkyl halides to form higher-order amines.

• Acylation: Amines react with acyl chlorides to form amides.

• Formation of amine salts: Amines react with acids to form water-soluble salts.

Reactions of Amides

• Hydrolysis: Amides can be hydrolyzed under acidic or basic conditions to yield carboxylic acids and amines or ammonia.

• Acidic hydrolysis: $RCONH_2 + H_2O + H^+ \rightarrow RCOOH + NH_4^+$

• Basic hydrolysis: $RCONH_2 + OH^- \rightarrow RCOO^- + NH_3$

Biological and Industrial Importance

• Amines are found in amino acids, neurotransmitters, and pharmaceuticals.

• Amides are present in proteins (peptide bonds) and synthetic polymers (e.g., nylon).

Special Topics

Alkaloids

• Alkaloids are naturally occurring amines found in plants, often with pharmacological effects.

• Examples: Quinine, caffeine, nicotine.

Polymerization

• Amides are formed in the production of polyamides (e.g., nylon) via condensation reactions between diamines and dicarboxylic acids.

Tables

Classification of Amines and Amides

Compound Type	General Formula	Example
Primary Amine	RNH2	CH3NH2 (Methylamine)
Secondary Amine	R2NH	(CH3)2NH (Dimethylamine)
Tertiary Amine	R3N	N(CH3)3 (Trimethylamine)
Primary Amide	RCONH2	CH3CONH2 (Acetamide)
Secondary Amide	RCONHR'	CH3CONHCH3 (N-Methylacetamide)
Tertiary Amide	RCONR'2	CH3CON(CH3)2 (N,N-Dimethylacetamide)

Comparison of Amines and Amides

Property	Amines	Amides
Basicity	Strong base	Weak base
Hydrogen Bonding	Moderate (primary/secondary)	Strong
Boiling Point	Lower than alcohols	Higher than amines
Solubility	Good (primary/secondary)	Good (simple amides)

Key Equations

• Formation of Amine Salt: $RNH_2 + HCl \rightarrow RNH_3^+Cl^-$

• Hydrolysis of Amide (Acidic): $RCONH_2 + H_2O + H^+ \rightarrow RCOOH + NH_4^+$

• Hydrolysis of Amide (Basic): $RCONH_2 + OH^- \rightarrow RCOO^- + NH_3$

Examples and Applications

• Example of a primary amine: Methylamine ($CH_3NH_2$)

• Example of a secondary amine: Dimethylamine ($CH_3NHCH_3$)

• Example of a primary amide: Acetamide ($CH_3CONH_2$)

• Example of a naturally occurring amide: Urea ($NH_2CONH_2$)

Summary Table: Key Reactions

Reaction	Reactants	Products
Alkylation	Amines + Alkyl halide	Higher-order amines
Acylation	Amines + Acyl chloride	Amides
Hydrolysis (acidic)	Amide + Acid + Water	Carboxylic acid + Ammonium ion
Hydrolysis (basic)	Amide + Base	Carboxylate ion + Ammonia

Additional info:

• Some questions referenced alkaloids, polymerization, and biological amides, which are important in advanced organic and biochemistry topics.

• Classification and nomenclature are essential for understanding reactivity and properties.