# Organic synthesis

> CIE A-Level Chemistry · CIE 9701 (2022-2024)
> Source: https://www.owlsprep.com/study/cie-9701-u27-overview/
> Weight: n/a

This unit builds on your existing knowledge of organic functional groups to teach core problem-solving and calculation skills for organic synthesis, a key topic for structured CIE A-Level exam questions.

**Prerequisites:** [Knowledge of organic functional groups and their reactions](https://www.owlsprep.com/study/cie-9701-u18-functional-groups-overview/)

## Learning objectives

- Plan multi-step organic synthetic routes to convert starting materials to target products, including identifying correct reagents and conditions
- Calculate percentage yield and percentage purity for products of organic synthesis reactions
- Solve structured exam-style synthesis problems by combining prior functional group knowledge with core synthesis skills

## Unit at a Glance

Organic synthesis connects all the individual organic reaction concepts you have learned across your course into one applied skill set. This unit follows a logical learning arc: you will first master how to plan synthetic routes, then learn how to quantify how successful a given synthesis reaction is.

Both sub-topics are regularly assessed in structured paper 2 and 4 questions, so take time to practice planning and calculation skills as you work through the unit.

The unit is split into two core sub-topics:
- [Synthetic route planning](https://www.owlsprep.com/study/cie-9701-u27-synthetic-route-planning/) — Learn to construct multi-step synthetic routes, including retrosynthesis approaches to solve complex planning problems.
- [Yield and purity calculations](https://www.owlsprep.com/study/cie-9701-u27-yield-and-purity-calculations/) — Master common calculation types for yield and purity that are regularly tested in CIE exams.

## Common pitfalls

- **Wrong:** Omitting reaction conditions when writing synthetic routes
  - Why it fails: Examiner mark schemes award separate marks for correct conditions, not just correct reagents.
  - Correct: Always note specific reagents, catalysts, temperatures and solvents for each reaction step.
- **Wrong:** Mixing up percentage yield and percentage purity formulas
  - Why it fails: The two calculations use different reference values, so confusion leads to incorrect final answers.
  - Correct: Remember yield compares actual product to theoretical product, while purity compares pure product mass to total impure sample mass.

## Cheatsheet

| Concept / Formula | Description |
| --- | --- |
| $\text{Percentage yield} = \frac{\text{actual mass of product}}{\text{theoretical mass of product}} \times 100\%$ | Measures how much product is produced compared to the maximum expected from reactants |
| $\text{Percentage purity} = \frac{\text{mass of pure product}}{\text{total mass of impure sample}} \times 100\%$ | Measures how much of a collected sample is pure product, rather than contaminants |
| Retrosynthesis rule | Work backwards from the target product when stuck to identify required reaction steps |
| Always check functional group change | Confirm what type of reaction (oxidation, substitution, addition etc.) is needed before selecting reagents |
| Yield vs atom economy | Yield measures how much product you get; atom economy measures how much reactant mass is incorporated into the desired product |

## What's next

Begin this unit by working through the first sub-topic on synthetic route planning to build core problem-solving skills. Once you complete both sub-topics in this unit, you can move on to the next unit covering analytical techniques for organic compound identification.

- [Synthetic route planning](https://www.owlsprep.com/study/cie-9701-u27-synthetic-route-planning/)
- [Yield and purity calculations](https://www.owlsprep.com/study/cie-9701-u27-yield-and-purity-calculations/)
- [Nuclear magnetic resonance spectroscopy](https://www.owlsprep.com/study/cie-9701-u28-overview/)

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