Organic Chemistry (AS)

Alkanes (Saturated Hydrocarbons)

• Combustion: Complete and incomplete.
• Free-radical Substitution.
• Cracking: Conversion of alkane to alkene + alkane (requires no oxygen, high temperature, zeolite catalyst).

Alkenes (Unsaturated Hydrocarbons)

• Addition Reactions:
  • Hydrogen: CH2=CH2 + H2 → CH3CH3 (requires 140°C, Ni catalyst).
  • Steam: CH2=CH2 + H2O → CH3CH2OH (requires 330°C, 6MPa, H3PO4 catalyst).
  • Hydrogen Halides: CH2=CH2 + HBr → CH3CH2Br (conc. HX, r.t.p.).
  • Halogens: CH2=CH2 + Br2 → CH2BrCH2Br (r.t.p.).
• Oxidation:
  • Cold dilute acidified KMnO4.
  • Hot concentrated acidified KMnO4.
• Addition Polymerisation.
• Test for C=C bond: Decolourisation of Br2.

Halogenoalkanes

• Substitution (Nucleophilic):
  • Aqueous Alkali (OH⁻): CH3CH2Br + NaOH → CH3CH2OH + NaBr.
  • KCN (CN⁻ in ethanol): CH3CH2Br + CN⁻ → CH3CH2CN + Br⁻.
  • Ammonia (NH3 in ethanol): CH3CH2Br + NH3 → CH3CH2NH2 + HBr.
• Mechanism:
  • Primary: SN2 mechanism.
  • Tertiary: SN1 mechanism.
  • Secondary: Both SN1 and SN2.
• Elimination: CH3CHBrCH3 + NaOH(ethanol) → CH2=CHCH3 + H2O + NaBr.

Alcohols

• Properties: Higher boiling point due to hydrogen bonding.
• Combustion: C2H5OH + 3O2 → 2CO2 + 3H2O.
• Substitution: Formation of halogenoalkanes.
• Esterification: CH3CH2COOH + CH3CH2OH → CH3CH2COOC2H5 + H2O.
• Hydrolysis of Esters:
  • Acid-catalysed: Reversible.
  • Alkali-catalysed: Complete hydrolysis to alcohol and carboxylic acid salt.
• Dehydration (Elimination): CH3CH2OH → CH2=CH2 + H2O.
• Oxidation:
  • Primary alcohol: Aldehyde then carboxylic acid (reflux).
  • Secondary alcohol: Ketone.
  • Tertiary alcohol: No reaction.

Nitriles

• Hydrolysis: CH3CH2CN + HCl + 2H2O → CH3CH2COOH + NH4Cl.
• Reduction: CN + 4[H] → CH2NH2.

Carboxylic Acids

• Dissociation: CH3COOH ↔ CH3COO⁻ + H⁺.
• Neutralisation: With alkalis, reactive metals, and carbonates.
• Reduction: CH3COOH + 4[H] → CH3CH2OH + H2O.

Aldehydes & Ketones

• Reduction: Aldehyde to primary alcohol; ketone to secondary alcohol.
• Nucleophilic Addition with HCN: Increases hydrocarbon chain length.
• Testing for Carbonyl Group:
  • Tri-iodomethane test.
  • Tollens’ reagent.
  • Fehling’s solution.
  • 2,4-DNPH test.

Organic Chemistry (A-level)

Benzene and Arenes

• Structure: Planar, symmetrical with delocalised π bonds.
• Substitution Reactions (Electrophilic):
  • Halogenation: Requires FeCl3, AlCl3, or FeBr3.
  • Nitration: Using conc. HNO3 & H2SO4.
  • Friedel-Crafts Alkylation/Acylation.
• Oxidation of Side-chain: Converts to carboxylic acid.

Phenol

• Properties: Weakly acidic, forms stable phenoxide ion.
• Reactions:
  • With NaOH and Na.
  • Electrophilic substitution more readily than benzene.

Amines

• Types: Primary, secondary, tertiary.
• Acidity and Basicity: Depend on electron-donating/withdrawing groups.
• Reactions:
  • Formation of amines via reduction.
  • Electrophilic substitution reactions.
  • Diazotisation and azo dye formation.

Amino Acids

• Structure: RCH(NH2)COOH.
• Properties: Form zwitterions, can act as buffers.
• Reactions:
  • Form dipeptides through condensation.

Amides

• Formation: Reaction of acyl chlorides with NH3 or amines.
• Hydrolysis: Produces carboxylic acid and amines or ammonia.

Acyl Chlorides

• Reactivity: High, used in synthesis.
• Reactions:
  • Hydrolysis to form carboxylic acids.
  • Esterification with alcohols.
  • Nucleophilic substitution with amines.