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*Revision Materials* 1 Atomic Structure 2 Atoms, molecules and stoichiometry 3 Chemical Bonding 4 States of matter 5 Chemical energetics 6 Electrochemistry 7 Equilibria 8 Reaction kinetics 9 The Periodic Table, chemical periodicity 10 Group 2 11 Group 17 12 Nitrogen and sulfur 13 Organic 14 Hydrocarbons 15 Halogen compounds 16 Hydroxy compounds 17 Carbonyl compounds 18 Carboxylic acids and derivatives 19 Nitrogen compounds 20 Polymerisation 21 Organic synthesis 22 Analytical techniques 23 Chemical energetics 24 Electrochemistry 25 Equilibria 26 Reaction kinetics 27 Group 2 28 Chemistry of transition elements 29 Organic 30 Hydrocarbons 31 Halogen compounds 32 Hydroxy compounds 33 Carboxylic acids and derivatives 34 Nitrogen compounds 35 Polymerisation 36 Organic synthesis 37 Analytical techniques

21 Organic synthesis

21.1 Organic synthesis

Organic synthesis

Specification Reference Organic Chemistry, Organic synthesis 21.1

Quick Notes

  • You need to be able to identify functional groups using tests and reactions covered in previous organic modules.
  • Predict how compounds will react based on their functional groups.
  • Use known reactions to build multi-step synthesis routes
    • (e.g. alcohol → halogenoalkane → nitrile → carboxylic acid).
    For each step, determine:
    • Reagents and conditions
    • Type of reaction (e.g. substitution, oxidation, reduction)
    • Any possible by-products (e.g. HCl, H2O, salts)

Full Notes

Identification of Functional Groups

Use the reactions and tests covered across the syllabus to identify key functional groups, such as:

Functional Group Test or Reaction Example Observation
Alkene Bromine water Orange to colourless
Alcohol Na metal, PCl5, acidified K2Cr2O7 Effervescence, steamy fumes, colour change
Aldehyde Tollens’ or Fehling’s solution Silver mirror or red precipitate
Ketone 2,4-DNPH Orange precipitate
Carboxylic acid Na2CO3 Effervescence (CO2 released)
Amine Reaction with HCl, ethanoyl chloride Fishy smell, white fumes
Ester Hydrolysis + pH check / smell Fruity smell, changes in pH

Predicting Properties and Reactions

Use known reactivities of functional groups:

Understand reaction patterns:

Devising Synthetic Routes

Break complex synthesis into smaller steps, and select appropriate reactions to move between functional groups.

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Matt’s exam tip

Synthesis questions can look overwhelming! Focus on one thing at a time and remember that no matter how complicated the molecules may look, the functional group conversions will only be ones you have seen and learnt about before. Focus on the functional groups in the molecules that are changing, rather than focusing on the whole molecules overall.

Example Synthesising Ethylamine (C2H5NH2) from Ethene (C2H4)

A typical exam question may get you to fill in missing steps for a synthesis. Such as making ethylamine from ethene.

CIE A-Level Chemistry multi-step synthesis prompt showing ethene converting through three steps to ethylamine, with missing reagents to be filled in.

A possible route may be.

  1. Hydration of Ethene to Ethanol
    Reagents: Steam, H3PO4 catalyst
    C2H4 + H2O → C2H5OH
  2. Conversion of Ethanol to Bromoethane
    Reagents: HBr
    C2H5OH + HBr → C2H5Br + H2O
  3. Nucleophilic Substitution with Ammonia
    Reagents: Excess NH3
    C2H5Br + NH3 → C2H5NH2 + HBr
CIE A-Level Chemistry completed route showing ethene hydrated to ethanol, converted to bromoethane, then to ethylamine using excess ammonia.

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