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
Worked example
Suggest how the following syntheses could be carried out:
a) Chloroethane to ethanoic acid
b) Ethene to 1-aminopropane
Answer 1
Answer 2
Exam Tip
You could be required to design a synthesis with up to four steps.