Chemistry · 9701 · 6 min read · Updated 2026-05-11
Synthetic route planning — CIE A-Level Chemistry
CIE A-Level Chemistry · 9701 · 6 min read
1. Retrosynthetic Analysis Basics★★☆☆☆⏱ 10 min
Retrosynthesis simplifies complex planning problems by reducing the size of the target molecule step-by-step, making it easier to identify viable starting materials and reaction sequences.
Exam tip: Always use retrosynthetic arrows (not standard reaction arrows) for retrosynthetic analysis to earn full marks
2. Selecting Reagents and Conditions★★★☆☆⏱ 15 min
After mapping your route, you need to specify the correct reagents and conditions for every step. CIE marking schemes award heavy marks for correct conditions, so they must not be omitted.
3. Planning a Full 3-Step Synthetic Route★★★★☆⏱ 20 min
To plan a full forwards route, combine the results of your retrosynthetic analysis with your knowledge of reagents. Always check that existing functional groups are not affected by each step, and adjust the order of reactions if needed.
Exam tip: Always write reagents and conditions clearly for every step, even if the step seems obvious
4. Evaluating Alternative Synthetic Routes★★★★☆⏱ 15 min
CIE questions often ask you to select the best route from multiple options. Evaluate routes based on these key criteria:
Overall yield: Fewer steps generally give higher yield, but high-yield multiple steps are better than low-yield single steps
Side reactions: Routes that avoid unwanted reactions at other functional groups are preferred
Cost: Cheaper starting materials and reagents are better
Safety: Less toxic reagents are preferred
Purity: Routes that produce easily purified product are better
Common Pitfalls
Why: Examiners expect correct notation to demonstrate understanding of backwards planning
Why: Without reflux and excess oxidant, only the aldehyde intermediate will form
Why: CIE marking schemes award 1 mark per step for correct conditions, which are easy marks to lose
Why: A one-step reversible route with low yield is worse than a two-step route with high yield per step
Why: Oxidising agents will react with double bonds and alcohols, leading to unwanted side products