Organic Synthesis (AQA A Level Chemistry)

Organic Synthesis

• It is possible to make a large number of organic products from a few starting compounds and the necessary reagents and conditions

• Knowing how organic functional groups are related to each other is key to the synthesis of a given molecule

• The main functional groups you need to know are

  • Alkanes

  • Alkenes

  • Halogenoalkanes

  • Alcohols

  • Carbonyls (aldehydes & ketones)

  • Carboxylic acids

  • Carboxylic acid derivatives

  • Amines

  • Nitriles

  • Arenes

Aliphatic Reaction Pathways

• The key functional groups and their interconversions are summarised here:

The diagram shows the main reaction pathways in aliphatic chemistry

Aliphatic Reactions Table

Aromatic Reaction Pathways

• The key aromatic reactions are summarised here:

Some of the key reaction pathways in aromatic chemistry

Aromatic Reactions Table

Choosing A Reaction Pathway

• Chemists will often have several choices of reaching a target molecule and those choices need to take into the principles of green chemistry

The twelve principles of green chemistry

• By choosing a pathway that has fewer steps, you can prevent waste and reduce energy demands which is better for the environment

  • This also reduces production costs

• By analysing the atom economy of each step, you can select reactions that give a higher atom economy

• Choosing alternative safer solvents also follows the principles of green chemistry

Designing a Reaction Pathway

• The given molecule is usually called the target molecule and chemists try to design a synthesis as efficiently as possible

• Designing a reaction pathway starts by drawing the structures of the target molecule and the starting molecule

• Determine if they have the same number of carbon atoms

  • If you need to lengthen the carbon chain you will need to put on a nitrile group by nucleophilic substitution

• Work out all the compounds that can be made from the starting molecule and all the molecules that can be made into the target molecule

  • Match the groups they have in common and work out the reagents and conditions needed