IGCSE organic chemistry reaction map: alkanes, alkenes, alcohols, carboxylic acids, esters and polymers

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• 1. Cracking · Core

  From → toLong alkane → Alkene

  Conditions and catalystHigh temperature + a catalyst (4CH1: silica or alumina at 600–700 °C); a shorter alkane or H₂ forms too

  Example equationC₁₀H₂₂ → C₈H₁₈ + C₂H₄

• 2. Hydrogenation · Extended

  From → toAlkene → Alkane

  Conditions and catalystH₂ with a nickel catalyst

  Example equationC₂H₄ + H₂ → C₂H₆

• 3. Hydration (steam) · Core

  From → toAlkene → Alcohol

  Conditions and catalystSteam, 300 °C, 6000 kPa (60 atm), acid catalyst (usually phosphoric acid)

  Example equationC₂H₄ + H₂O → C₂H₅OH

• 4. Addition polymerisation · Core

  From → toAlkene → Addition polymer

  Conditions and catalystMany monomers: each C=C opens and they join into a long chain

  Example equationn CH₂=CH₂ → –(CH₂–CH₂)ₙ–

• 5. Substitution by chlorine · Extended

  From → toAlkane → Chloroalkane

  Conditions and catalystCl₂ and ultraviolet light (provides the activation energy)

  Example equationCH₄ + Cl₂ → CH₃Cl + HCl

• 6. Fermentation · Core

  From → toGlucose → Alcohol

  Conditions and catalystYeast, 25–35 °C, in the absence of oxygen

  Example equationC₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

• 7. Oxidation · Extended

  From → toAlcohol → Carboxylic acid

  Conditions and catalystWarm with acidified aqueous potassium manganate(VII) (purple → colourless), or bacterial oxidation in making vinegar

  Example equationC₂H₅OH + 2[O] → CH₃COOH + H₂O

• 8. Esterification · Extended

  From → toCarboxylic acid + Alcohol → Ester

  Conditions and catalystAlcohol + carboxylic acid, warm, acid catalyst (usually concentrated H₂SO₄)

  Example equationCH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O

• Combustion · Core

  From → toAlkane / alcohol → CO₂ + H₂O

  Conditions and catalystEnough oxygen = complete; too little gives toxic CO and soot (C)

  Example equationC₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

• Ethanoic acid + metal / base / carbonate · Core

  From → toCarboxylic acid → an ethanoate salt

  Conditions and catalystMetal → salt + H₂ · base → salt + water · carbonate → salt + water + CO₂

  Example equation2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂

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• Alkane

  Functional groupC–C single bonds only (saturated)

  General formulaCₙH₂ₙ₊₂

  Examplemethane CH₄ · ethane C₂H₆

  Name ends in-ane

• Alkene

  Functional groupC=C (unsaturated)

  General formulaCₙH₂ₙ

  Exampleethene C₂H₄ · propene C₃H₆

  Name ends in-ene

• Alcohol

  Functional group–OH

  General formulaCₙH₂ₙ₊₁OH

  Exampleethanol C₂H₅OH

  Name ends in-ol

• Carboxylic acid

  Functional group–COOH

  General formulaCₙH₂ₙ₊₁COOH

  Exampleethanoic acid CH₃COOH

  Name ends in-oic acid

• Ester

  Functional group–COO–

  General formula—

  Exampleethyl ethanoate CH₃COOC₂H₅

  Name ends in-yl -oate

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• An alkene (unsaturated)

  TestShake with aqueous bromine

  Result (exam wording)orange to colourless (the bromine is decolourised)

• An alkane (saturated)

  TestShake with aqueous bromine

  Result (exam wording)stays orange (no colour change)

• A carboxylic acid

  TestAdd sodium carbonate

  Result (exam wording)effervescence; the gas turns limewater milky

• An alcohol being oxidised (Extended)

  TestWarm with acidified potassium manganate(VII)

  Result (exam wording)purple to colourless

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• Raw material

  FermentationGlucose from plants: renewable

  Hydration of etheneEthene from crude oil (cracking): non-renewable

• Conditions

  FermentationYeast, 25–35 °C, no oxygen

  Hydration of ethene300 °C, 6000 kPa, acid catalyst

• Rate

  FermentationSlow, batch process

  Hydration of etheneFast, continuous process

• Purity

  FermentationA dilute solution that needs fractional distillation

  Hydration of etheneHigh-purity ethanol

• Energy

  FermentationLow temperature, little energy

  Hydration of etheneHigh temperature and pressure, a lot of energy

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• methanol

  Acidethanoic acid

  Ester (name)methyl ethanoate

  FormulaCH₃COOCH₃

• ethanol

  Acidethanoic acid

  Ester (name)ethyl ethanoate

  FormulaCH₃COOC₂H₅

• ethanol

  Acidmethanoic acid

  Ester (name)ethyl methanoate

  FormulaHCOOC₂H₅

• propan-1-ol

  Acidethanoic acid

  Ester (name)propyl ethanoate

  FormulaCH₃COOC₃H₇

• methanol

  Acidpropanoic acid

  Ester (name)methyl propanoate

  FormulaC₂H₅COOCH₃

• butan-1-ol

  Acidmethanoic acid

  Ester (name)butyl methanoate

  FormulaHCOOC₄H₉

1. 1Draw the monomer as a displayed formula, showing the C=C and all 4 groups on it.
2. 2Open the double bond: C=C becomes a C–C single bond, and a bond (arm) comes out of each carbon.
3. 3Put brackets round the 2 carbons with the arms through the brackets, and write n at the bottom right. Other groups (CH₃, Cl) stay where they were.
4. 4Join them into a chain: 3 repeat units in a row, the backbone carbons in one line, no double bond left.

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• Ester from ethanol + methanoic acid

  Loses the markmethyl ethanoate

  Scoresethyl methanoate

• Bromine water with an alkene

  Loses the markturns clear

  Scoresorange to colourless

• Hydration conditions

  Loses the markheat ethene with water

  Scoressteam, 300 °C, 6000 kPa, acid catalyst

• Fermentation conditions

  Loses the markyeast at 100 °C in air

  Scoresyeast, 25–35 °C, in the absence of oxygen

• Hydrogenation catalyst

  Loses the markiron / platinum catalyst

  Scoresnickel catalyst

• Substitution by chlorine

  Loses the markheat methane with chlorine

  Scoresultraviolet light (provides the activation energy)

• Addition polymer repeat unit

  Loses the markkeeps the C=C inside the brackets

  ScoresC–C single bond, with the bonds extending through the brackets

• Addition vs condensation

  Loses the markaddition polymerisation also gives water

  Scoresaddition: only one product · condensation: polymer + a small molecule (water)