OCR A-Level Chemistry Paper H432/02: 6 Must-Know Topics That Maximise Marks
If you're taking the OCR A-Level Chemistry Paper 2 (H432/02 Synthesis and Analytical Technqiues) soon, it's tempting to try to revise every topic equally.
The problem is that Paper 2 doesn't test topics in isolation.
Many questions combine several areas of organic chemistry into one larger synthesis, mechanism or analysis problem. That's why students who understand the links between topics often outperform those who simply memorise individual facts.
Here are 6 topics worth prioritising in the final days and weeks before your exam.
Alkenes
Alkenes sit at the centre of many organic reaction pathways.
You should be confident with electrophilic addition and know the products formed when alkenes react with:
| Reagent | Conditions | Organic Product Formed |
|---|---|---|
| Br₂ | Room temperature | Dibromoalkane |
| HBr | Room temperature | Bromoalkane* |
| H₂ | Nickel catalyst, heat | Alkane |
| H₂O (steam) | H₃PO₄ catalyst, high temperature and pressure | Alcohol |
*Unsymmetrical alkenes can form major and minor products depending on where the H and Br add across the double bond.Why does this matter?
Because alkene reactions frequently appear as intermediate steps in longer synthesis questions. If you struggle here, you can lose marks throughout an entire pathway.
Exam insight: Make sure you can identify the major product and recognise when more than one product could form.
Alcohols
Alcohols connect multiple areas of the OCR specification.
Students should be comfortable with:
Oxidation reactions
Nucleophilic substitution
Elimination reactions
You need to know how alcohols react with:
| Reagent | Conditions | Organic Product Formed |
|---|---|---|
| Cr₂O₇²⁻/H⁺ | Distillation (primary alcohol) | Aldehyde |
| Cr₂O₇²⁻/H⁺ | Reflux (primary alcohol) | Carboxylic acid |
| Cr₂O₇²⁻/H⁺ | Reflux (secondary alcohol) | Ketone |
| NaBr/H₂SO₄ | Heat under reflux | Bromoalkane |
| Concentrated H₂SO₄ | Heat | Alkene |
When examiners create multi-step synthesis questions, alcohols often act as the bridge between different functional groups.
Stereoisomerism
Stereochemistry regularly appears inside larger questions rather than as a standalone topic.
Make sure you can:
Identify chiral centres
Recognise optical isomers
Draw E-Z isomers correctly
Explain why molecules show stereoisomerism
Students often know the chemistry but forget to consider stereochemistry, which can cost valuable marks.
| Compound Type | Possible Isomerism | What to Check |
|---|---|---|
| Alkene | E-Z isomerism | Two different groups attached to each carbon of the C=C |
| Amino Acid* | Optical isomerism | Presence of a chiral carbon |
| Transition Metal Complexes | Cis-trans / Optical isomerism | Arrangement of ligands around the metal ion |
*Remember: Glycine does not contain a chiral centre.
Benzene
Benzene questions are often highly structured and tend to be predictable. From structure and stability to reactions, make sure you can compare reactivity of benzene to alkenes, phenols and other substituted arenes.
Focus on understanding electrophilic substitution, with each of these reagents:
| Reagent | Conditions | Organic Product Formed |
|---|---|---|
| HNO₃/H₂SO₄ | Warm, under reflux | Nitrobenzene |
| Cl₂/AlCl₃ | Anhydrous catalyst | Chlorobenzene |
| CH₃Cl/AlCl₃ | Anhydrous catalyst | Methylbenzene |
| CH₃COCl/AlCl₃ | Anhydrous catalyst | Phenylethanone |
One common mistake is confusing electrophilic substitution with electrophilic addition.
The benzene ring remains intact throughout the reaction. Examiners expect you to recognise and explain this.
Carbonyl Compounds
Aldehydes and ketones appear regularly in OCR A-Level Chemistry.
You should be confident with:
| Reagent | Conditions | Organic Product Formed |
|---|---|---|
| NaBH₄ | Aqueous solution | Alcohol |
| Cr₂O₇²⁻/H⁺ | Reflux (aldehydes only) | Carboxylic acid |
| 2,4-DNPH | Room temperature | Orange precipitate (carbonyl identified) |
| Tollens' Reagent | Warm gently | Silver mirror (aldehydes only) |
Reduction using sodium borohydride
Oxidation of aldehydes
Nucleophilic addition mechanisms
Qualitative tests for carbonyl compounds
Carbonyl chemistry often forms part of larger synthesis pathways, making it a high-value revision area.
Combined Analysis
Many of the highest-mark questions in Paper 2 involve interpreting evidence from multiple analytical techniques.
Make sure you can confidently use:
| Technique | Key Information to Identify |
|---|---|
| ¹³C NMR | Number of carbon environments, chemical shifts |
| ¹H NMR | Chemical shifts, integration, splitting patterns |
| IR Spectroscopy | Functional groups (O-H, C=O, N-H) |
| Mass Spectrometry | Molecular ion peak (M⁺), fragmentation patterns |
Students who can combine all four techniques quickly often gain a significant advantage in Paper 2.
What Examiners Are Actually Looking For
OCR examiners are not simply testing whether you can memorise reactions.
They're assessing whether you can:
Link topics together
Apply knowledge in unfamiliar contexts
Predict reaction outcomes
Analyse evidence logically
Communicate mechanisms accurately
This is why these six topics are so valuable. They appear repeatedly across the paper and often connect several areas of the specification, leading to a series of quick wins.
Action Steps Before Your Paper 2 Exam
✅ Learn the key reagents and conditions for each topic
✅ Practise drawing mechanisms from memory
✅ Complete synthesis pathway questions under timed conditions
✅ Review stereochemistry mistakes from past papers
✅ Practise combined NMR, IR and mass spectrometry questions
Tutor Insight
The students who make the biggest jump from a B to an A grade usually don't revise more. They revise smarter. Instead of treating organic chemistry as a collection of separate topics, they learn how the reactions connect. That kind of application is what sets the A grade students apart from the B grade students. To revise strategically for paper 3, start early.
Next Step
If you're preparing for A-Level Chemistry exams and want structured support with exam technique, and A/A* model answers to commonly asked exam questions, download my Free 5 Most Examined A-Level Chemistry Topics Guide with Model A/A* Answers to help you revise strategically.
FAQs
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There isn't a single most important topic, but alkenes, alcohols, carbonyls and analytical techniques consistently appear and often connect multiple concepts. As a general rule, make sure you understand how to synthesise different compounds from different reactants, and the core A-Level mechanisms and common reagents.
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Focus on reaction pathways, mechanisms and combined analysis questions where you identify an unknown compound. These areas often carry a large number of marks and reward deeper understanding, and are examined year on year.
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Many students memorise reactions in isolation, but struggle to link topics together. Paper 2 frequently tests synthesis pathways that require knowledge from several parts of the specification. And of course, sound knowledge of how curly arrows work in mechanisms is key.
