AQA A Level Chemistry

Revision Notes

7.8.1 Organic Synthesis

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:

Organic reaction pathways- aliphatic, downloadable AS & A Level Chemistry revision notes

The diagrams shows the main reaction pathways in aliphatic chemistry

Aliphatic Reactions Table

Organic reaction pathways Aliphatic Table 2, downloadable AS & A Level Chemistry revision notes

Aromatic Reaction Pathways

  • The key aromatic reactions are summarised here:

Organic reaction pathways- aromatic, downloadable AS & A Level Chemistry revision notes

Some of the key reaction pathways in aromatic chemistry

Aromatic Reactions Table

Organic reaction pathways- Aromatic Table, downloadable AS & A Level Chemistry revision notes

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, downloadable AS & A Level Chemistry revision notes

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

Worked Example

Suggest how the following syntheses could be carried out:

a) Chloroethane to ethanoic acid

b) Ethene to 1-aminopropane

Answer 1

Organic synthesis WE Answer 1, downloadable AS & A Level Chemistry revision notes

 

Answer 2

Organic synthesis WE Answer 2, downloadable AS & A Level Chemistry revision notes

Exam Tip

You could be required to design a synthesis with up to four steps.

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