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

• Designing a reaction pathway involves planning a sequence of reactions to convert a starting molecule into a target molecule

• Synthetic routes are designed to form this compound as efficiently as possible from the given starting material

• Begin by drawing the structures of both the starting molecule and the target molecule

• Compare the number of carbon atoms in each compound

  • If the target molecule contains more carbon atoms, the carbon chain may need to be extended

  • One method is to introduce a nitrile group (–CN) via nucleophilic substitution, which increases the carbon chain length by one carbon atom

• Next, identify the functional groups present in the starting compound and determine which reactions it can undergo

  • Then consider which functional groups are present in the target molecule and how they can be formed

• Look for possible intermediate compounds that could link the starting material to the target molecule

  • Match functional groups carefully and specify the appropriate reagents and conditions for each step in the pathway