Topic 19

An organic compound containing a –NH₂ group attached to a carbon chain.

Primary amine: –NH₂ attached to one carbon
Secondary amine: –NH attached to two carbons
Tertiary amine: N attached to three carbons

Organic compound with –CONH₂ (carbonyl attached to NH₂).

Can be primary (–CONH₂), secondary (–CONHR), tertiary (–CONR₂)

A molecule containing both an amino group (–NH₂) and a carboxylic acid group (–COOH)

General formula: H₂N–CH(R)–COOH
R = side chain (defines the amino acid)

They act as bases → accept H⁺ → form alkaline solution.

Equation:
CH₃CH₂CH₂CH₂NH₂ + H₂O → CH₃CH₂CH₂CH₂NH₃⁺ + OH⁻

Tip: Solution turns blue with universal indicator.

Forms an alkaline solution.

Reaction: CH₃CH₂CH₂CH₂NH₂ + H₂O → CH₃CH₂CH₂CH₂NH₃⁺ + OH⁻
Observation: Solution is basic (pH > 7)
Type: Amine acts as a base by accepting H⁺
Conditions: Room temperature, aqueous solution

Forms a slightly alkaline solution.

Reaction: C₆H₅NH₂ + H₂O ⇌ C₆H₅NH₃⁺ + OH⁻
Observation: Weakly basic because lone pair on N delocalized into benzene ring
Conditions: Room temperature, aqueous solution

Amines react with acids to form ammonium salts.

Butylamine + HCl: CH₃CH₂CH₂CH₂NH₂ + HCl → CH₃CH₂CH₂CH₂NH₃⁺Cl⁻
Phenylamine + HCl: C₆H₅NH₂ + HCl → C₆H₅NH₃⁺Cl⁻
Observation: Solid salt forms on evaporation
Conditions: Room temperature, aqueous acid

-Amines act as nucleophiles, replacing halogen.

-Butylamine example: CH₃CH₂CH₂CH₂NH₂ + CH₃CH₂Br → CH₃CH₂CH₂CH₂NHCH₂CH₃ + HBr

-Phenylamine: Much slower reaction due to electron delocalization, may need heat in ethanol

ethanol (to prevent hydrolysis)

-Conditions: heat under Reflux, ethanol (to prevent hydrolysis)

: Forms amide.

Butylamine: CH₃CH₂CH₂CH₂NH₂ + CH₃COCl → CH₃CH₂CH₂CH₂NHCOCH₃ + HCl
Phenylamine: C₆H₅NH₂ + CH₃COCl → C₆H₅NHCOCH₃ + HCl
Observation: HCl gas evolves
Conditions: Room temperature, usually in dry conditions

Butylamine: [Cu(H₂O)₆]²⁺ + 4CH₃CH₂CH₂CH₂NH₂ → [Cu(CH₃CH₂CH₂CH₂NH₂)₄(H₂O)₂]²⁺ + 4H₂O
Conditions: Aqueous solution, room temperature

the lone pair of electrons on the nitrogen atom forms hydrogen bonds with the hydrogen atoms in water molecules

Alkyl groups are electron donating (push electrons towards nitrogen) which causes a positive inductive effect → lone pair on N is more available → can accept H⁺ more easily.

Lone pair on N delocalized into the benzene ring → less available to accept H⁺.

By nucleophilic substitution using excess ammonia (NH₃).

Reaction: CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br

Conditions:

ethanloic solution of halogenoalkane
Heat under pressure in a sealed tube

itrile (R–C≡N) is reduced to primary amine (R–CH₂NH₂).

Reaction: CH₃CH₂C≡N + 4[H] → CH₃CH₂CH₂NH₂

Reagents/Conditions:
-LiAlH₄ in dry ether (strong reducing agent, lab method)
OR
-H₂ with Ni catalyst
Type: Reduction

By reduction of aromatic nitro-benze using tin (Sn) and concentrated HCl.

Reaction (overall):
C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O
Reagents: Sn (tin) and concentrated HCl
Type: Reduction

-Heat under reflux with Sn and concentrated HCl
-Aqueous environment

By nitration of benzene.

Reaction: C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O
Reagents/Conditions:
HNO3(conc.)+ H2SO4(conc.)
Warm below 55°C
Type: Electrophilic substitution

By reaction of aromatic amine with nitrous acid (HNO₂).

-(Formation of HNO2): NaNO₂ + HCl --> NaCl + HNO2

Reaction: C₆H₅NH₂ + HNO₂ + HCl → C₆H₅N₂⁺Cl⁻ + 2H₂O

-Conditions:
-0–5°C (ice-cold) to stabilize diazonium ion

-Above 5°C, diazonium ion decomposes → forms phenol or other side products
-Cold stabilizes N₂⁺ group, ready for coupling reaction

Diazonium ion reacts with electron-rich phenol to form an azo dye.

-Reaction: C₆H₅N₂⁺Cl⁻ + C₆H₅OH → C₆H₅–N=N–C₆H₄OH + HCl
-Conditions: Alkaline conditions

By reaction of acyl chloride with ammonia or amines.

Reaction with ammonia (NH₃):
CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl
Reaction with primary amine (R’NH₂):
CH₃–C=O–Cl + 2NH₃ → CH₃–C=O–NH₂ + NH₄Cl

-To react with HCl produced → prevents formation of HCl fumes
-Ensures formation of amide, not ammonium salt only

Room temperature
Dry conditions preferred (water reacts violently with acyl chlorides)
Often done in ethanol as solvent

Polymer formed when monomers with two functional groups react, eliminating a small molecule (usually water).

Example:
Reaction: –COOH + –NH₂ → –CONH– + H₂O


rule: eliminate OH from (COOH) and H from (NH2)

Two functional groups on monomers (diacid + diamine, or diol + dicarboxylic acid)
Small molecule eliminated (H₂O, HCl)
Can be polyamide or polyester depending on monomers

Polymer formed when unsaturated monomers (alkenes) join without loss of small molecules.

Reaction: Double bonds (C=C) break → form long chain

Example 1: Poly(propeneamide)
Monomer: CH₂=CH–CONH₂
Reaction: n CH₂=CH–CONH₂ → –[CH₂–CH(CONH₂)]ₙ–

: Because of hydrogen bonding between –CONH– groups in the polymer chain.

Hydrogen bonds form between C=O (δ⁻) and N–H (δ⁺)
Observation: Strong, rigid fibers (e.g., nylon, proteins)

Hydrogen bonding occurs between polymer chains (intermolecular), not with water
Polymer is too large to dissolve → insoluble

–OH groups along the polymer chain can form hydrogen bonds with water molecules
Soluble because polymer is hydrophilic

Example in everyday life:
-Soluble laundry bags (poly(ethenol) dissolves in water in washing machine)
-Liquid detergent capsules (Liquitabs) dissolve in water

: Amino acids can act as both acids and bases → amphoteric.

Method:
Dissolve amino acid in water → add acid (HCl) → reacts with –NH₂ → forms –NH₃⁺
Dissolve amino acid in water → add alkali (NaOH) → reacts with –COOH → forms –COO⁻

Amino acids react with both acids and bases → zwitterion formation

By condensation polymerisation of amino acids

Method: Heat amino acids → –COOH reacts with –NH₂ → peptide bond (-CONH-) forms + H₂O
Reaction:
H₂N–CH(R)–COOH + H₂N–CH(R’)–COOH → H₂N–CH(R)–CONH–CH(R’)–COOH + H₂O
Observation: Formation of dipeptides or polypeptides

A zwitterion is a molecule that has both a positive and a negative charge on different atoms but is overall electrically neutral.

In amino acids: –NH₃⁺ (positive) and –COO⁻ (negative) exist on the same molecule.
Formed in aqueous solution at the isoelectric point.