Start with the two structures
Begin by drawing or identifying the structures of the starting molecule and the target molecule. This makes changes in carbon number and functional group easier to recognise.
- Count the carbon atoms in the starting molecule and the target molecule.
- Identify the functional groups present in each.
- Ask which known reaction could produce the target functional group.
- Identify a possible intermediate linking the starting material to the target.
- Specify the reagent and essential conditions for every step.
Plan backwards, then check forwards
The target functional group can suggest a suitable compound immediately before it in the synthesis. Continue this reasoning until the proposed intermediates connect back to the given starting molecule.
Planning direction: start from the target and ask which known functional-group transformation could have produced it. Repeat this for each proposed intermediate until the given starting material is reached.
Then read the route forwards. Every intermediate must genuinely be obtainable from the compound before it and must be able to undergo the next proposed reaction.
Exam Tip: Show a clear sequence of structures and give the reagent and essential condition for every arrow. Starting from the target and identifying the previous functional group can make a route easier to construct.