Multi-step Synthetic Routes (Cambridge International A-Level Chemistry)

Spec point — 21.1.2

Multi-Step Synthetic Routes

• A large number of organic products are made from a few starting compounds using appropriate 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
  • Haloalkanes
  • Nitriles
  • Amines
  • Alcohols
  • Carbonyls (aldehydes & ketones)
  • Hydroxynitriles
  • Carboxylic acids
  • Esters
  • Acyl chlorides
  • Primary and secondary amides

Exam Hint You also need to be able to identify the functional groups of these chemicals in structures that are given to you

Aliphatic Reaction Pathways

• The key interconversions between functional groups are summarised here:

Aliphatic Reactions Table

Aromatic Reaction Pathways

• The key aromatic reactions are summarised here:

Aromatic Reactions Table

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

Worked Example Suggest how the following synthesis could be carried out:

Ethene to 1-aminopropane

Answer

Exam Hint Sound knowledge of all of the different reactions is beneficial as the A-level course simply states that you should be able to design a multistage synthesis

Past papers generally go to four steps in a multistep reaction although there is no clear limit stated