Organic Synthesis (Oxford AQA International A Level Chemistry)

Organic Synthesis

• 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

  • Halogenoalkanes

  • Nitriles

  • Amines

  • Alcohols

  • Carbonyls (aldehydes & ketones)

  • Hydroxynitriles

  • Carboxylic acids

  • Esters

  • Acyl chlorides

  • Primary and secondary amides

Aliphatic reaction pathways

• The key interconversions between functional groups are summarised here:

Aliphatic reactions map

Aliphatic reactions table

Aromatic reaction pathways

• The key aromatic reactions are summarised here:

Aromatic reactions map

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 principles of green chemistry

• The key principles to consider are:

  • Not using a solvent, if possible

    • Solvents typically require removing at the end of a reaction

    • This has energy and environmental implications

  • Using non-hazardous starting materials

    • The use of hazardous materials means that there are health, safety and environmental considerations, which often impact the overall time and financial cost of a synthetic scheme

  • Using fewer steps

    • Choosing a pathway that has fewer steps prevents waste, reduces energy demands (which is better for the environment) and can reduce production costs

  • Using steps / reaction that have a high percentage atom economy

    • Higher atom economy means that there is less waste and the reaction is more chemically efficient, which often results in lower costs

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

• 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