Organic Synthesis (AQA A Level Chemistry): Revision Note

Organic synthesis

• A wide range of organic products can be made from just a few starting compounds, given the right reagents and conditions.

• Understanding how different organic functional groups interconvert is key to designing synthetic routes.

• The main functional groups you need to know are:

  • Alkanes

  • Alkenes

  • Halogenoalkanes

  • Alcohols

  • Carbonyls (aldehydes & ketones)

  • Carboxylic acids and derivatives

  • Amines

  • Nitriles

  • Arenes

Aliphatic reaction pathways

• The key transformations between these functional groups are summarised in the diagram and table below:

Aliphatic reactions table

Aromatic reaction pathways

• The most important reactions of aromatic compounds are summarised below:

Aromatic reactions table

Choosing a reaction pathway

• Chemists often have several possible ways to make a target molecule

  • The best route balances efficiency, safety, and sustainability

• Choosing a route with fewer steps reduces waste and energy use

  • This is better for the environment and more cost-effective

• Reactions with high atom economy are preferred

  • They maximise the use of starting materials

• Safer solvents and less hazardous reagents are also key considerations

Designing a reaction pathway

• The compound you are trying to make is called the target molecule

• Synthetic routes are designed to make it as efficiently as possible from a given starting molecule

• Start by drawing both structures

• Check whether the target has more carbon atoms than the starting material:

  • If so, a nitrile group can be introduced via nucleophilic substitution to lengthen the chain

• Then:

  • Work out what molecules the starting compound can be converted int

  • Work out what molecules can be converted into the target

  • Look for overlap

    • Match functional groups and map out the reagents and conditions

• Being able to combine these reactions in multi-step syntheses is a key exam skill

  • Practise working backwards from target molecules