01
Alkanes
Alkanes are saturated hydrocarbons — they contain only C–C single bonds. General formula: CnH2n+2. They are relatively unreactive due to the strength of C–H and C–C bonds, but they do undergo free radical substitution and combustion.
Oxidation Combustion
▾
Complete Combustion
CH4 + 2O2
⟶
CO2 + 2H2O
Condition: Excess O2, high temperature (burning in air)
Condition: Excess O2, high temperature (burning in air)
Incomplete Combustion
CH4 + O2
⟶
C + 2H2O
(limited O2 → soot)
Or: 2CH4 + 3O2 ⟶ 2CO + 4H2O
Or: 2CH4 + 3O2 ⟶ 2CO + 4H2O
Key fact: CO is a toxic, odourless gas. Complete combustion gives CO₂ + H₂O only.
Substitution Free Radical Halogenation
▾
CH4 + Cl2
⟶
CH3Cl + HCl
Condition: UV light (hν), gas phase
Condition: UV light (hν), gas phase
⚙ Free Radical Substitution Mechanism
1
Initiation: UV light breaks Cl–Cl homolytically →
Cl–Cl → 2Cl• (each Cl gets one electron)2
Propagation (step 1):
Cl• + CH₄ → CH₃• + HCl3
Propagation (step 2):
CH₃• + Cl₂ → CH₃Cl + Cl•4
Termination: Two radicals combine, e.g.
Cl• + Cl• → Cl₂ or CH₃• + Cl• → CH₃ClRemember: Curly arrows show electron pair movement. Half-headed arrows (fish-hook) show single electron movement in radical reactions. Multiple substitution can occur giving CH₂Cl₂, CHCl₃, CCl₄.
Thermal Cracking
▾
Thermal Cracking
C10H22
⟶
C5H12 + C5H10
Condition: 700–1000°C, high pressure, no catalyst → produces alkenes + alkanes
Condition: 700–1000°C, high pressure, no catalyst → produces alkenes + alkanes
Catalytic Cracking
Condition: Zeolite catalyst (aluminium silicate), 450°C, lower pressure
Produces branched alkanes + aromatic compounds (petrol)
Produces branched alkanes + aromatic compounds (petrol)
Why crack? Long-chain alkanes are less useful. Cracking produces shorter, more useful molecules including alkenes (monomers for polymers).
02
Alkenes
Alkenes contain a C=C double bond. General formula: CnH2n. The π bond is electron-rich and makes alkenes electrophilic addition targets. They are much more reactive than alkanes.
Addition Hydrogenation
▾
CH2=CH2 + H2
⟶
CH3–CH3
Condition: Ni catalyst, 150°C, high pressure
Condition: Ni catalyst, 150°C, high pressure
Industrial use: Hardening vegetable oils to make margarine (converting liquid unsaturated fats to solid saturated fats).
Addition Electrophilic Addition of HBr (+ Markovnikov's Rule)
▾
CH3–CH=CH2 + HBr
⟶
CH3–CHBr–CH3 (major)
+ CH3–CH2–CH2Br (minor)
Condition: Room temperature, no catalyst needed
+ CH3–CH2–CH2Br (minor)
Condition: Room temperature, no catalyst needed
⚙ Electrophilic Addition Mechanism
1
Step 1 (slow): The H–Br bond is polarised (Hδ+–Brδ−). The π electrons attack the Hδ+. A C–H bond forms and a
carbocation (C+) forms. Br⁻ is released.2
Step 2 (fast): Br⁻ attacks the carbocation → C–Br bond forms.
3
Markovnikov's Rule: H adds to the carbon with MORE H atoms already. This gives the MORE STABLE (more substituted) carbocation intermediate:
secondary > primary.
Addition Bromine Water Test
▾
CH2=CH2 + Br2
⟶
CH2Br–CH2Br
Condition: Room temperature, Br₂ in water (orange → colourless)
Condition: Room temperature, Br₂ in water (orange → colourless)
Test for C=C: Shake with orange bromine water — if it decolorises → alkene is present.
⚙ Mechanism — Electrophilic Addition via Bromonium Ion
1
Br₂ is polarised (Brδ+–Brδ−) near the electron-rich π bond. The π electrons attack Brδ+.
2
A cyclic
bromonium ion intermediate forms + Br⁻ leaves.3
Br⁻ attacks from the back →
anti addition product (trans dibromo).
Addition Hydration (making alcohol)
▾
CH2=CH2 + H2O
⟶
CH3CH2OH
Condition: H₃PO₄ catalyst, 300°C, 60 atm
Condition: H₃PO₄ catalyst, 300°C, 60 atm
Industrial route to making ethanol. The steam is passed over the catalyst with ethene.
Oxidation Oxidation with KMnO4
▾
Cold, dilute KMnO₄ (acidified):
CH2=CH2 + [O] + H2O ⟶ CH2OH–CH2OH (diol)
Purple → colourless: test for C=C
Hot, concentrated KMnO₄:
Breaks the C=C → forms carboxylic acids (from R–CH=) or CO₂+H₂O (from CH₂=)
CH2=CH2 + [O] + H2O ⟶ CH2OH–CH2OH (diol)
Purple → colourless: test for C=C
Hot, concentrated KMnO₄:
Breaks the C=C → forms carboxylic acids (from R–CH=) or CO₂+H₂O (from CH₂=)
Polymer Addition Polymerisation
▾
n CH2=CH2
⟶
–[CH2–CH2]n– (poly(ethene))
Condition: High pressure OR Ziegler–Natta catalyst, moderate temperature
Condition: High pressure OR Ziegler–Natta catalyst, moderate temperature
Note: Each monomer must contain a C=C. The double bond opens up to join the chain. Repeat unit shown in square brackets.
03
Benzene & Arenes
Benzene (C6H6) is a planar, cyclic molecule with a delocalised π electron system. All C–C bonds are equivalent (length between single and double). The extra stability of benzene (delocalisation energy ≈ 150 kJ/mol) means it prefers electrophilic substitution (preserving the ring) over addition.
Substitution Nitration
▾
C6H6 + HNO3
⟶
C6H5NO2 (nitrobenzene) + H2O
Condition: Conc. H₂SO₄ catalyst, conc. HNO₃, 50°C (below 55°C to avoid dinitration)
Condition: Conc. H₂SO₄ catalyst, conc. HNO₃, 50°C (below 55°C to avoid dinitration)
⚙ Electrophilic Substitution Mechanism
1
Generate electrophile: H₂SO₄ protonates HNO₃ →
NO₂⁺ (nitronium ion) is formed: HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂O2
Attack: π electrons of benzene attack NO₂⁺ → forms a
carbocation intermediate (arenium ion). Ring loses aromaticity temporarily.3
Restoration: H⁺ lost from ring carbon → aromaticity restored. H⁺ + HSO₄⁻ → H₂SO₄ (catalyst regenerated).
Substitution Halogenation (Friedel-Crafts)
▾
C6H6 + Cl2
⟶
C6H5Cl (chlorobenzene) + HCl
Condition: AlCl₃ (halogen carrier/Lewis acid catalyst), anhydrous, room temperature
Condition: AlCl₃ (halogen carrier/Lewis acid catalyst), anhydrous, room temperature
⚙ Mechanism
1
Electrophile generation: AlCl₃ + Cl₂ →
Cl⁺ (polarised Cl–Cl via AlCl₃: Cl–Cl→AlCl₃ gives δ+Cl–δ−Cl–AlCl₃)2
π electrons attack Cl⁺ → arenium ion intermediate.
3
Loss of H⁺ restores ring; H⁺ + AlCl₄⁻ → HCl + AlCl₃ (regenerated).
Substitution Friedel-Crafts Acylation
▾
C6H6 + CH3COCl
⟶
C6H5COCH3 (phenylethanone / acetophenone) + HCl
Condition: AlCl₃ (anhydrous), room temperature
Condition: AlCl₃ (anhydrous), room temperature
⚙ Mechanism
1
AlCl₃ activates acyl chloride → generates acylium ion
CH₃CO⁺2
Acylium ion attacks benzene ring (electrophilic substitution as before).
Alkylation uses RCl + AlCl₃ to add an alkyl group. Acylation adds an acyl group (–COR) — preferred as it doesn't give polysubstituted products.
Substitution Sulfonation
▾
C6H6 + H2SO4
⇌
C6H5SO3H (benzenesulfonic acid) + H2O
Condition: Fuming H₂SO₄ (oleum), warm (~80°C). Reversible reaction.
Condition: Fuming H₂SO₄ (oleum), warm (~80°C). Reversible reaction.
Electrophile is SO₃ (from oleum). The reaction is reversible — heating with steam removes SO₃H group.
Reduction Reduction of Nitrobenzene → Aniline
▾
C6H5NO2 + 6[H]
⟶
C6H5NH2 (aniline / phenylamine) + 2H2O
Condition: Sn metal + conc. HCl, heat (then NaOH to liberate free amine)
Condition: Sn metal + conc. HCl, heat (then NaOH to liberate free amine)
Industrial route to dyes & drugs. Sn acts as reducing agent. The product aniline is a primary aromatic amine — key starting material for azo dyes.
04
Alcohols
Alcohols contain the –OH group. They are classified as primary (1°), secondary (2°) or tertiary (3°) based on how many carbon groups are attached to the carbon bearing –OH. This affects their oxidation reactions.
Oxidation Combustion
▾
C2H5OH + 3O2
⟶
2CO2 + 3H2O
Condition: Excess O₂, ignition
Condition: Excess O₂, ignition
Oxidation Oxidation with K₂Cr₂O₇
▾
| Alcohol Type | Product (Gentle) | Product (Excess) |
|---|---|---|
| Primary (1°) e.g. CH₃CH₂OH | Aldehyde: CH₃CHO (distil off immediately) | Carboxylic acid: CH₃COOH (reflux) |
| Secondary (2°) e.g. (CH₃)₂CHOH | Ketone: (CH₃)₂C=O | Ketone only (cannot oxidise further) |
| Tertiary (3°) e.g. (CH₃)₃COH | No reaction (no H on C–OH) | |
Reagent: K₂Cr₂O₇/H₂SO₄ (acidified dichromate)
Colour change: orange → green (Cr²⁷⁺ → Cr³⁺) confirms oxidation
Colour change: orange → green (Cr²⁷⁺ → Cr³⁺) confirms oxidation
Tollens' reagent (silver mirror test) distinguishes aldehyde from ketone — aldehydes are oxidised further, ketones are NOT.
Elimination Dehydration → Alkene
▾
CH3CH2OH
⟶
CH2=CH2 + H2O
Condition: Conc. H₂SO₄ or Al₂O₃ (catalyst), 170°C
Condition: Conc. H₂SO₄ or Al₂O₃ (catalyst), 170°C
Note: At 140°C with conc. H₂SO₄, etherification occurs instead: 2CH₃CH₂OH → CH₃CH₂OCH₂CH₃ + H₂O (intermolecular dehydration).
Substitution Making Halogenoalkanes
▾
Using HX:
CH3CH2OH + HBr ⟶ CH3CH2Br + H2O
Condition: NaBr + conc. H₂SO₄, heat (generates HBr in situ)
Using PCl₅:
C2H5OH + PCl₅ ⟶ C2H5Cl + POCl₃ + HCl
Condition: Room temperature — also test for –OH group (steamy fumes of HCl)
Using SOCl₂:
C2H5OH + SOCl₂ ⟶ C2H5Cl + SO₂ + HCl
CH3CH2OH + HBr ⟶ CH3CH2Br + H2O
Condition: NaBr + conc. H₂SO₄, heat (generates HBr in situ)
Using PCl₅:
C2H5OH + PCl₅ ⟶ C2H5Cl + POCl₃ + HCl
Condition: Room temperature — also test for –OH group (steamy fumes of HCl)
Using SOCl₂:
C2H5OH + SOCl₂ ⟶ C2H5Cl + SO₂ + HCl
Condensation Esterification
▾
CH3COOH + C2H5OH
⇌
CH3COOC2H5 (ethyl ethanoate) + H2O
Condition: Conc. H₂SO₄ catalyst, heat. Equilibrium reaction — remove water to shift right.
Condition: Conc. H₂SO₄ catalyst, heat. Equilibrium reaction — remove water to shift right.
Ester functional group: –COO– (ester linkage). The O in –OH of acid bonds with H of alcohol's –OH → H₂O lost. Esters smell fruity.
05
Phenols
Phenol (C6H5OH) has an –OH group directly on a benzene ring. The lone pair on O delocalises into the ring, activating it (especially at ortho/para positions) and making O–H more acidic than in alcohols (but still a weak acid, pKa ≈ 10).
Acid-Base Phenol as an Acid
▾
C6H5OH + NaOH
⟶
C6H5O⁻Na⁺ (sodium phenoxide) + H2O
Condition: Room temperature, aqueous NaOH
Condition: Room temperature, aqueous NaOH
C6H5OH + Na2CO3
→ NO REACTION
Phenol is a WEAKER acid than carbonic acid (H₂CO₃) — cannot displace CO₂
Phenol is a WEAKER acid than carbonic acid (H₂CO₃) — cannot displace CO₂
Distinguish from carboxylic acid: Carboxylic acids react with Na₂CO₃ to give CO₂ bubbles; phenol does NOT.
Condensation Ester Formation with Phenol
▾
C6H5OH + CH3COCl
⟶
C6H5OOCCH3 (phenyl ethanoate) + HCl
Condition: Room temperature, no catalyst needed (acyl chloride is reactive enough)
Condition: Room temperature, no catalyst needed (acyl chloride is reactive enough)
Why use acyl chloride, not carboxylic acid? Phenol is a weaker nucleophile than alcohol; acid catalyst + heating not enough. Acyl chlorides react at room temperature.
Substitution Bromination of Phenol
▾
C6H5OH + 3Br2(aq)
⟶
2,4,6-tribromophenol + 3HBr
Condition: Room temperature, bromine WATER (no catalyst needed — ring is activated)
Bromine water decolorises immediately + white precipitate forms
Condition: Room temperature, bromine WATER (no catalyst needed — ring is activated)
Bromine water decolorises immediately + white precipitate forms
Compare with benzene: Benzene needs a Lewis acid catalyst (AlBr₃) to react with Br₂. Phenol is so reactive it reacts with Br₂ in water directly — and gives trisubstituted product.
Test Phenol + FeCl₃
▾
C6H5OH + FeCl3(aq)
⟶
Purple/violet complex
Condition: Add a few drops of FeCl₃ solution to phenol
Condition: Add a few drops of FeCl₃ solution to phenol
Diagnostic test: Purple/violet colour with neutral FeCl₃ confirms phenolic –OH group is present.
06
Halogenoalkanes
Halogenoalkanes (haloalkanes) contain a C–X bond (X = F, Cl, Br, I). The C–X bond is polar (Cδ+–Xδ−) making carbon electrophilic and susceptible to nucleophilic substitution and elimination.
Substitution SN1 vs SN2 Mechanism
▾
| Feature | SN1 | SN2 |
|---|---|---|
| Steps | 2 (stepwise) | 1 (concerted) |
| Intermediate | Carbocation | None |
| Favoured by | Tertiary halides | Primary halides |
| Rate depends on | [RX] only | [RX] and [Nu⁻] |
| Stereochemistry | Racemisation | Inversion (Walden) |
⚙ SN2 Mechanism (e.g. CH₃Br + OH⁻)
1
OH⁻ attacks from the back (180°) of C–Br bond. C–Br starts to break simultaneously.
2
Transition state:
HO···C···Br (pentavalent)3
Br⁻ leaves → C–OH forms. Configuration inverted (umbrella effect).
⚙ SN1 Mechanism (e.g. (CH₃)₃CBr + H₂O)
1
Step 1 (slow, RDS): C–Br ionises → stable
3° carbocation + Br⁻2
Step 2 (fast): Nucleophile (H₂O, OH⁻) attacks carbocation from either face → racemisation
Substitution Nucleophilic Substitution Reactions
▾
| Nucleophile | Reagent & Conditions | Product |
|---|---|---|
| OH⁻ (hydrolysis) | NaOH(aq), warm | Alcohol (–OH) |
| CN⁻ | KCN in ethanol, warm | Nitrile (–CN) — chain extended by 1C |
| NH₃ | Excess conc. NH₃, heat in sealed tube | Primary amine (–NH₂) |
| RNH₂ (amine) | Excess RNH₂, heat | Secondary amine |
| I⁻ (Finkelstein) | NaI in acetone | Iodoalkane |
Hydrolysis example:
CH3CH2Br + NaOH(aq) ⟶ CH3CH2OH + NaBr
Condition: aqueous NaOH, warm
CH3CH2Br + NaOH(aq) ⟶ CH3CH2OH + NaBr
Condition: aqueous NaOH, warm
Elimination E2 Elimination → Alkene
▾
CH3CH2Br + NaOH
⟶
CH2=CH2 + NaBr + H2O
Condition: NaOH in ethanol (not water), heat
Condition: NaOH in ethanol (not water), heat
SN2 vs E2: Aqueous NaOH → substitution (alcohol). Ethanolic NaOH + heat → elimination (alkene). Tertiary halides favour elimination more than primary.
⚙ E2 Mechanism
1
OH⁻ acts as BASE, abstracting H from β-carbon (the carbon next to C–Br).
2
As H–C bond breaks, C=C π bond forms simultaneously and Br⁻ leaves. All in one concerted step.
Reactivity C–X Bond Strength & Reactivity
▾
Reactivity order: C–I > C–Br > C–Cl > C–F
Bond enthalpy (kJ/mol): C–F(484) > C–Cl(338) > C–Br(276) > C–I(238)
Weaker bond = easier to break = faster reaction
Bond enthalpy (kJ/mol): C–F(484) > C–Cl(338) > C–Br(276) > C–I(238)
Weaker bond = easier to break = faster reaction
Test for halogenoalkanes: Add AgNO₃ in ethanol after hydrolyis. AgCl = white ppt, AgBr = cream ppt, AgI = yellow ppt. Solubility in NH₃ confirms: AgCl dissolves in dilute NH₃; AgBr in conc. NH₃; AgI insoluble.
07
Carbonyl Compounds: Aldehydes & Ketones
Both contain the C=O (carbonyl) group. Aldehydes have –CHO at the end of a chain; ketones have C=O within the chain. The C=O is polar (Cδ+) → susceptible to nucleophilic addition.
Reduction Reduction with NaBH₄ / LiAlH₄
▾
Aldehyde → Primary alcohol:
CH3CHO + 2[H] ⟶ CH3CH2OH
Ketone → Secondary alcohol:
CH3COCH3 + 2[H] ⟶ CH3CH(OH)CH3
Reagent: NaBH₄ in water/ethanol (mild) OR LiAlH₄ in dry ether (powerful)
CH3CHO + 2[H] ⟶ CH3CH2OH
Ketone → Secondary alcohol:
CH3COCH3 + 2[H] ⟶ CH3CH(OH)CH3
Reagent: NaBH₄ in water/ethanol (mild) OR LiAlH₄ in dry ether (powerful)
⚙ Nucleophilic Addition Mechanism
1
H⁻ (hydride ion from NaBH₄) attacks the electrophilic Cδ+ of C=O.
2
C=O π bond breaks → alkoxide ion (C–O⁻) forms.
3
Protonation (H₂O or H⁺) → alcohol.
Addition Addition of HCN (Cyanohydrin)
▾
CH3CHO + HCN
⟶
CH3CH(OH)CN (2-hydroxypropanenitrile)
Condition: KCN/HCN, dilute acid, room temperature. NaCN + H₂SO₄ generates HCN safely.
Condition: KCN/HCN, dilute acid, room temperature. NaCN + H₂SO₄ generates HCN safely.
⚙ Mechanism
1
CN⁻ (nucleophile) attacks Cδ+ of C=O → C–CN bond forms, C–O⁻ created.
2
Protonation of O⁻ by H⁺ (from HCN dissociation) → –OH group.
Importance: Extends carbon chain by 1C. The –CN can be hydrolysed to –COOH (carboxylic acid) — useful in synthesis. Creates a chiral centre → racemic mixture forms.
Condensation 2,4-DNPH Test (Brady's Reagent)
▾
R–C=O + H2N–NHRC6H3(NO2)2
⟶
Orange/yellow precipitate + H2O
Condition: 2,4-dinitrophenylhydrazine solution, add to carbonyl compound
Condition: 2,4-dinitrophenylhydrazine solution, add to carbonyl compound
Test result: Orange/yellow precipitate = carbonyl group present. Recrystallise the ppt and measure melting point to identify which specific aldehyde or ketone.
Test Distinguishing Aldehyde from Ketone
▾
| Test | Reagent | Aldehyde | Ketone |
|---|---|---|---|
| Tollens' | AgNO₃ + NH₃ (silver mirror reagent) | Silver mirror on tube wall | No reaction |
| Fehling's | Blue Cu²⁺ solution, warm | Brick-red ppt (Cu₂O) | No reaction |
| K₂Cr₂O₇ | Acidified dichromate | Orange → green | No colour change |
Tollens: RCHO + 2[Ag(NH₃)₂]⁺ + 2OH⁻
⟶
RCOO⁻ + 2Ag↓ + 4NH₃ + H₂O
Key: Aldehydes can be oxidised (they have H on C=O); ketones cannot (no H on C=O carbon).
Test Triiodomethane (Iodoform) Reaction
▾
CH3COR + 3I2 + 3NaOH
⟶
CHI3↓ (yellow ppt) + RCOONa + 3NaI + 3H₂O
Condition: I₂ + NaOH (warm)
Condition: I₂ + NaOH (warm)
Positive test: Yellow precipitate of CHI₃ (triiodomethane) with antiseptic smell. Tests for CH₃CO– (methyl ketones like propanone) AND CH₃CH(OH)– (ethanol and secondary alcohols with CH₃– next to C–OH).
08
Carboxylic Acids & Derivatives
Carboxylic acids contain –COOH. They are weak acids. Derivatives include: acyl chlorides (–COCl), acid anhydrides (–CO–O–CO–), esters (–COO–), and amides (–CONH₂). Reactivity order: acyl chloride > anhydride > ester > amide.
Acid Reactions of Carboxylic Acids
▾
With bases (Na, NaOH, Na₂CO₃):
CH3COOH + NaOH → CH3COONa + H₂O
2CH3COOH + Na2CO3 → 2CH3COONa + CO₂↑ + H₂O
With alcohols (esterification):
CH3COOH + CH3OH ⇌ CH3COOCH3 + H₂O
Condition: Conc. H₂SO₄ catalyst, heat
CH3COOH + NaOH → CH3COONa + H₂O
2CH3COOH + Na2CO3 → 2CH3COONa + CO₂↑ + H₂O
With alcohols (esterification):
CH3COOH + CH3OH ⇌ CH3COOCH3 + H₂O
Condition: Conc. H₂SO₄ catalyst, heat
Reduction Reduction of Carboxylic Acids
▾
CH3COOH + 4[H]
⟶
CH3CH2OH + H2O
Condition: LiAlH₄ in dry ether (NaBH₄ is NOT strong enough for carboxylic acids)
Condition: LiAlH₄ in dry ether (NaBH₄ is NOT strong enough for carboxylic acids)
Substitution Reactions of Acyl Chlorides (–COCl)
▾
| Nucleophile | Reaction | Product | Conditions |
|---|---|---|---|
| H₂O | Hydrolysis | Carboxylic acid + HCl | Cold water, vigorous |
| ROH (alcohol) | Esterification | Ester + HCl | Room temperature |
| NH₃ | Amide formation | Amide + NH₄Cl | Room temperature, excess NH₃ |
| RNH₂ (amine) | N-substituted amide | RCONHR + HCl | Room temperature |
| ArOH (phenol) | Esterification | Phenyl ester + HCl | Room temperature |
CH3COCl + CH3OH
⟶
CH3COOCH3 + HCl (steamy fumes)
⚙ Nucleophilic Acyl Substitution Mechanism
1
Nucleophile (e.g. –OH of alcohol) attacks electrophilic C of C=O in acyl chloride → tetrahedral intermediate.
2
Cl⁻ leaves as the C=O reforms → ester product + HCl.
Substitution Reactions of Acid Anhydrides
▾
With water:
(CH3CO)2O + H2O → 2CH3COOH
With alcohol:
(CH3CO)2O + C2H5OH → CH3COOC2H5 + CH3COOH
With ammonia:
(CH3CO)2O + 2NH3 → CH3CONH2 + CH3COONH₄
Safer than acyl chloride (no HCl fumes); used in aspirin synthesis
(CH3CO)2O + H2O → 2CH3COOH
With alcohol:
(CH3CO)2O + C2H5OH → CH3COOC2H5 + CH3COOH
With ammonia:
(CH3CO)2O + 2NH3 → CH3CONH2 + CH3COONH₄
Safer than acyl chloride (no HCl fumes); used in aspirin synthesis
Hydrolysis Ester Hydrolysis
▾
Acid hydrolysis (reversible):
CH3COOC2H5 + H2O ⇌ CH3COOH + C2H5OH
Condition: Dilute H₂SO₄, heat under reflux
Base (saponification) — irreversible:
CH3COOC2H5 + NaOH ⟶ CH3COO⁻Na⁺ + C2H5OH
Condition: NaOH(aq), heat under reflux
CH3COOC2H5 + H2O ⇌ CH3COOH + C2H5OH
Condition: Dilute H₂SO₄, heat under reflux
Base (saponification) — irreversible:
CH3COOC2H5 + NaOH ⟶ CH3COO⁻Na⁺ + C2H5OH
Condition: NaOH(aq), heat under reflux
Saponification (base hydrolysis) is irreversible because the carboxylate ion (RCOO⁻) is a poor electrophile — the alcohol cannot re-attack it to reform ester.
Hydrolysis Amide Reactions
▾
Acid hydrolysis:
CH3CONH2 + H2O + HCl ⟶ CH3COOH + NH₄Cl
Base hydrolysis:
CH3CONH2 + NaOH ⟶ CH3COO⁻Na⁺ + NH₃↑
Condition: Dilute acid or base, heat under reflux
Reduction of amide → amine:
CH3CONH2 + 4[H] ⟶ CH3CH2NH2 + H2O
Condition: LiAlH₄, dry ether
CH3CONH2 + H2O + HCl ⟶ CH3COOH + NH₄Cl
Base hydrolysis:
CH3CONH2 + NaOH ⟶ CH3COO⁻Na⁺ + NH₃↑
Condition: Dilute acid or base, heat under reflux
Reduction of amide → amine:
CH3CONH2 + 4[H] ⟶ CH3CH2NH2 + H2O
Condition: LiAlH₄, dry ether
09
Nitrogen Compounds
Includes amines (–NH₂, –NHR, –NR₂), amides (–CONH₂), nitriles (–C≡N), and amino acids. Amines are bases due to the lone pair on N. Primary amines can act as nucleophiles.
Base Amines as Bases & Nucleophiles
▾
As base:
CH3NH2 + HCl ⟶ CH3NH3⁺Cl⁻ (methylammonium chloride)
Basicity order:
Aliphatic: 2° > 1° > NH₃ > 3° (in water — due to solvation)
Aromatic amines (e.g. aniline C₆H₅NH₂) are MUCH weaker bases than aliphatic amines
(lone pair delocalised into benzene ring → less available for protonation)
CH3NH2 + HCl ⟶ CH3NH3⁺Cl⁻ (methylammonium chloride)
Basicity order:
Aliphatic: 2° > 1° > NH₃ > 3° (in water — due to solvation)
Aromatic amines (e.g. aniline C₆H₅NH₂) are MUCH weaker bases than aliphatic amines
(lone pair delocalised into benzene ring → less available for protonation)
Synthesis Making Amines
▾
| Method | Starting Material | Reagent & Conditions | Product |
|---|---|---|---|
| From halogenoalkane | RX | Excess NH₃, heat in sealed tube | RNH₂ (primary amine) — mixture of 1°/2°/3°/salt |
| Reduction of nitrile | R–CN | LiAlH₄ / dry ether OR H₂/Ni | R–CH₂NH₂ (1° amine, chain +1C) |
| Reduction of amide | RCONH₂ | LiAlH₄ / dry ether | RCH₂NH₂ |
| Reduction of nitrobenzene | C₆H₅NO₂ | Sn + conc. HCl, then NaOH | C₆H₅NH₂ (aniline) |
Condensation Amines + Acyl Chlorides → Amides
▾
CH3NH2 + CH3COCl
⟶
CH3CONHCH3 (N-methylethanamide) + HCl
Condition: Room temperature — very rapid reaction
Condition: Room temperature — very rapid reaction
Condensation Diazonium Salts & Azo Dyes
▾
Step 1 — Diazotisation:
C6H5NH2 + HCl + NaNO2 ⟶ [C6H5N≡N]⁺Cl⁻ (benzene diazonium chloride)
Condition: Below 5°C, HCl + NaNO₂ (NaNO₂ + HCl generates HNO₂ in situ)
Step 2 — Coupling reaction (azo dye):
[C6H5N≡N]⁺ + C6H5OH (phenol, alkaline) ⟶ C6H5–N=N–C6H4OH (orange/yellow azo dye)
Condition: Alkaline solution (NaOH), 0–5°C
C6H5NH2 + HCl + NaNO2 ⟶ [C6H5N≡N]⁺Cl⁻ (benzene diazonium chloride)
Condition: Below 5°C, HCl + NaNO₂ (NaNO₂ + HCl generates HNO₂ in situ)
Step 2 — Coupling reaction (azo dye):
[C6H5N≡N]⁺ + C6H5OH (phenol, alkaline) ⟶ C6H5–N=N–C6H4OH (orange/yellow azo dye)
Condition: Alkaline solution (NaOH), 0–5°C
Why keep below 5°C? Diazonium salts decompose above 10°C → phenol + N₂. Cold temperature stabilises them for coupling reactions.
Condensation Amino Acids & Peptide Bond
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Structure of amino acid (zwitterion at neutral pH):
⁺H₃N–CH(R)–COO⁻
Peptide bond formation (condensation):
H₂N–CHR–COOH + H₂N–CHR'–COOH ⟶ H₂N–CHR–CO–NH–CHR'–COOH + H₂O
Condition: Heat (in biology: enzyme-catalysed ribosome reaction)
⁺H₃N–CH(R)–COO⁻
Peptide bond formation (condensation):
H₂N–CHR–COOH + H₂N–CHR'–COOH ⟶ H₂N–CHR–CO–NH–CHR'–COOH + H₂O
Condition: Heat (in biology: enzyme-catalysed ribosome reaction)
Peptide bond: –CO–NH– linkage. Hydrolysis (acid/base + heat) breaks it back to amino acids. This is how proteins are broken down in digestion.
10
Polymer Chemistry
Polymers are long-chain molecules made from many repeating monomer units. Two main types: Addition polymers (from alkenes, no by-product) and Condensation polymers (from bifunctional monomers, with small by-product like H₂O or HCl).
Addition Addition Polymerisation
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| Monomer | Polymer | Uses |
|---|---|---|
| CH₂=CH₂ (ethene) | poly(ethene) –[CH₂–CH₂]n– | Plastic bags, bottles |
| CH₂=CHCl (chloroethene) | PVC –[CH₂–CHCl]n– | Pipes, flooring |
| CH₂=CHCN (propenenitrile) | PAN –[CH₂–CHCN]n– | Acrylic fibres |
| CF₂=CF₂ (tetrafluoroethene) | PTFE –[CF₂–CF₂]n– | Non-stick, wire insulation |
| CH₂=C(CH₃)COOCH₃ | Perspex (PMMA) | Transparent plastic |
n CH₂=CHX ⟶ –[CH₂–CHX]n–
No by-product formed. Double bond opens up.
No by-product formed. Double bond opens up.
Condensation Polyesters
▾
PET (Terylene/Dacron):
n HO–(CH₂)₂–OH (ethane-1,2-diol) + n HOOC–C₆H₄–COOH (benzene-1,4-dicarboxylic acid) ⟶ –[O–(CH₂)₂–O–CO–C₆H₄–CO]n– + n H₂O
Condition: High temperature, catalyst. Repeat unit has ester linkage –COO–
n HO–(CH₂)₂–OH (ethane-1,2-diol) + n HOOC–C₆H₄–COOH (benzene-1,4-dicarboxylic acid) ⟶ –[O–(CH₂)₂–O–CO–C₆H₄–CO]n– + n H₂O
Condition: High temperature, catalyst. Repeat unit has ester linkage –COO–
Monomers needed: A diol (2 × –OH) + a dicarboxylic acid (2 × –COOH). OR a hydroxy acid (–OH and –COOH in same molecule, e.g. lactic acid → poly(lactic acid)).
Condensation Polyamides (Nylon)
▾
Nylon-6,6:
n H₂N–(CH₂)₆–NH₂ (1,6-diaminohexane) + n ClOC–(CH₂)₄–COCl (hexanedioyl dichloride) ⟶ –[NH–(CH₂)₆–NH–CO–(CH₂)₄–CO]n– + n HCl
Condition: Room temperature (interfacial polymerisation) OR heat with diacid
Nylon-6 (from caprolactam — ring-opening):
n [–NH–(CH₂)₅–CO–] ⟶ –[NH–(CH₂)₅–CO]n–
n H₂N–(CH₂)₆–NH₂ (1,6-diaminohexane) + n ClOC–(CH₂)₄–COCl (hexanedioyl dichloride) ⟶ –[NH–(CH₂)₆–NH–CO–(CH₂)₄–CO]n– + n HCl
Condition: Room temperature (interfacial polymerisation) OR heat with diacid
Nylon-6 (from caprolactam — ring-opening):
n [–NH–(CH₂)₅–CO–] ⟶ –[NH–(CH₂)₅–CO]n–
Amide bond: –CO–NH–. Hydrogen bonding between chains makes nylon strong. Found in ropes, clothing, toothbrush bristles.
Natural Proteins & DNA as Natural Polymers
▾
Proteins: condensation polymer of amino acids → peptide bonds (–CONH–)
Starch/cellulose: condensation polymer of glucose → glycosidic bonds
DNA: condensation polymer of nucleotides → phosphodiester bonds
Starch/cellulose: condensation polymer of glucose → glycosidic bonds
DNA: condensation polymer of nucleotides → phosphodiester bonds
Hydrolysis of proteins: Acid (HCl) or base (NaOH) + heat breaks peptide bonds → mixture of amino acids. Enzymes do this in digestion at body temperature.
Properties Biodegradability of Polymers
▾
| Polymer type | Biodegradable? | Reason |
|---|---|---|
| Addition (e.g. polyethene) | NO | Only C–C and C–H bonds — very strong; microbes cannot break them |
| Condensation (polyesters, polyamides) | YES (slowly) | Ester/amide links can be hydrolysed by water, acid, base or enzymes |
| Proteins, starch | YES | Enzyme-catalysed hydrolysis by microorganisms |
Green chemistry: Poly(lactic acid) PLA — made from fermented starch — is a biodegradable polyester. Used in packaging and medical implants.
Self Assessment
📝 20-Question Quiz
Test your understanding of all 10 topics. Select an answer to reveal instant feedback.
Question 01 · Alkanes
What are the THREE stages of the free radical substitution of methane with chlorine?
Question 02 · Alkanes
UV light is used in the free radical halogenation of methane. What does UV light do?
Question 03 · Alkenes
Propene (CH₃CH=CH₂) reacts with HBr. Which product is the MAJOR product according to Markovnikov's Rule?
Question 04 · Alkenes
Bromine water (orange) is added to an unknown compound and it decolourises. What does this indicate?
Question 05 · Benzene
What electrophile is generated when benzene is nitrated using HNO₃/H₂SO₄?
Question 06 · Benzene
Why does benzene prefer electrophilic SUBSTITUTION rather than electrophilic ADDITION?
Question 07 · Alcohols
A secondary alcohol is heated with acidified K₂Cr₂O₇. What is the product?
Question 08 · Alcohols
Ethanol is heated with conc. H₂SO₄ at 170°C. What is the main product?
Question 09 · Phenols
Phenol is added to bromine water (no catalyst). What is observed and what is the product?
Question 10 · Halogenoalkanes
Which reagent and conditions would convert bromoethane to ethylamine (CH₃CH₂NH₂)?
Question 11 · Halogenoalkanes
Why is C–I bond more reactive than C–F bond in nucleophilic substitution?
Question 12 · Carbonyl Compounds
Tollens' reagent (ammoniacal AgNO₃) produces a silver mirror with compound X but NOT with compound Y. Both X and Y give an orange precipitate with 2,4-DNPH. What are X and Y?
Question 13 · Carbonyl Compounds
What is the product when HCN is added to ethanal (CH₃CHO)?
Question 14 · Carboxylic Acids
Why is base (saponification) hydrolysis of an ester irreversible, but acid hydrolysis is reversible?
Question 15 · Carboxylic Acids
An acyl chloride reacts with ammonia. What are the products?
Question 16 · Nitrogen Compounds
Why is aniline (C₆H₅NH₂) a much weaker base than methylamine (CH₃NH₂)?
Question 17 · Nitrogen Compounds
In diazotisation of aniline, why must the temperature be kept BELOW 5°C?
Question 18 · Polymers
What type of polymerisation makes PET (polyester) and what is the by-product?
Question 19 · Polymers
Why are addition polymers (like poly(ethene)) NOT biodegradable?
Question 20 · Mixed Topics
A compound gives a yellow precipitate with I₂/NaOH (iodoform test) AND decolourises acidified K₂Cr₂O₇. Which of the following could it be?