Organic chemistry can feel overwhelming when you have to remember dozens of reactions, reagents, conditions and mechanisms for your A Level Chemistry exams. One question might ask you to convert an alcohol into an alkene, while another requires you to identify a reaction pathway involving a halogenoalkane, nitrile or carboxylic acid.
The key to mastering organic chemistry is to understand how functional groups change during reactions rather than memorising isolated equations.
This guide provides an A Level Organic Chemistry reaction map covering the major functional groups, important reagents, reaction conditions, mechanisms and exam techniques. It is designed for UK students studying AQA, OCR or Pearson Edexcel, although the precise requirements differ between specifications.
Whether you are preparing for your next mock exam or revising for your final A Level Chemistry papers, use this guide to connect reactions and practise multi-step synthesis questions.
1. A Level Organic Chemistry Reaction Map
The first step is to understand how different organic compounds connect. Most organic synthesis questions require you to identify the starting functional group, determine the required product and select a suitable reaction.
Use the following map as your starting point.
| Starting compound | Reagent and conditions | Product |
|---|---|---|
| Alkane | Halogen, UV light | Halogenoalkane |
| Alkene | Hydrogen, nickel catalyst, heat | Alkane |
| Alkene | Steam, phosphoric acid catalyst, high temperature and pressure | Alcohol |
| Alkene | Hydrogen halide, such as HBr | Halogenoalkane |
| Alkene | Bromine water, room temperature | Dibromoalkane |
| Halogenoalkane | Aqueous NaOH or KOH, heat under reflux | Alcohol |
| Halogenoalkane | Ethanolic KOH, heat | Alkene |
| Halogenoalkane | KCN in ethanol, heat under reflux | Nitrile |
| Nitrile | Dilute acid or aqueous alkali, heat | Carboxylic acid or carboxylate, followed by acidification where needed |
| Nitrile | Reducing agent, such as LiAlH₄ under suitable conditions | Primary amine |
| Primary alcohol | Acidified potassium dichromate(VI), distil product | Aldehyde |
| Primary alcohol | Acidified potassium dichromate(VI), heat under reflux | Carboxylic acid |
| Secondary alcohol | Acidified potassium dichromate(VI), heat | Ketone |
| Alcohol | Concentrated sulfuric acid or phosphoric acid, heat | Alkene |
| Aldehyde or ketone | NaBH₄ in aqueous solution | Alcohol |
| Aldehyde or ketone | KCN followed by dilute acid | Hydroxynitrile |
| Carboxylic acid + alcohol | Concentrated sulfuric acid catalyst, heat | Ester |
| Acyl chloride + water | Room temperature | Carboxylic acid |
| Acyl chloride + alcohol | Suitable conditions, often room temperature | Ester |
| Acyl chloride + ammonia | Room temperature | Primary amide |
| Benzene | Concentrated nitric acid and concentrated sulfuric acid, warm | Nitrobenzene |
Important: This is a revision overview, not a complete list of every reaction required by every exam board. Check your own specification for the exact reagents, conditions and mechanisms you need to learn.
2. Alkanes: Substitution Reactions
Alkanes are saturated hydrocarbons containing only carbon–carbon single bonds. They are relatively unreactive, but they can react with halogens under ultraviolet light.
Reaction: Alkane to halogenoalkane
Example:
Methane + chlorine → chloromethane + hydrogen chloride
CH₄ + Cl₂ → CH₃Cl + HCl
Reagents and conditions: Chlorine and ultraviolet light.
Reaction type: Free-radical substitution.
The reaction proceeds through three stages:
- Initiation: ultraviolet light breaks the Cl–Cl bond by homolytic fission, forming chlorine radicals.
- Propagation: radicals react with molecules to generate new radicals, allowing the chain reaction to continue.
- Termination: radicals combine, removing radicals from the reaction mixture.
Exam tip
Do not confuse free-radical substitution with electrophilic addition. In substitution, a hydrogen atom is replaced by a halogen atom. In addition, atoms are added across a multiple bond.
3. Alkenes: Addition Reactions
Alkenes contain a carbon–carbon double bond. The double bond allows them to undergo addition reactions, making them useful starting materials for synthesising other organic compounds.
Hydrogenation: Alkene to alkane
Example:
Ethene + hydrogen → ethane
CH₂=CH₂ + H₂ → CH₃CH₃
Reagents and conditions: Hydrogen gas and a nickel catalyst, with heating.
Reaction type: Addition.
Hydration: Alkene to alcohol
Example:
Ethene + steam → ethanol
CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH
Reagents and conditions: Steam, phosphoric acid catalyst, elevated temperature and pressure.
This reaction is important because it demonstrates how an alkene can be converted into an alcohol.
Addition of a hydrogen halide
Example:
Propene reacts with hydrogen bromide to form bromopropanes, with 2-bromopropane generally favoured under ordinary conditions.
CH₃CH=CH₂ + HBr → CH₃CHBrCH₃
The product distribution depends on the structure of the alkene and the reaction conditions.
Test for unsaturation
Bromine water can be used to test for a carbon–carbon double bond. An alkene typically changes bromine water from orange to colourless.
Remember that a positive test indicates unsaturation under the test conditions; it does not identify the complete structure of an unknown compound.
4. Halogenoalkanes: Substitution and Elimination
Halogenoalkanes are particularly important in organic synthesis because they can form alcohols, alkenes, nitriles and amines.
Nucleophilic substitution: Halogenoalkane to alcohol
Example:
CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻
Reagents and conditions: Aqueous sodium hydroxide or potassium hydroxide, heated.
The hydroxide ion acts as a nucleophile, donating a lone pair to form a bond with the carbon atom attached to the halogen.
Elimination: Halogenoalkane to alkene
Example:
CH₃CH₂Br + OH⁻ → CH₂=CH₂ + H₂O + Br⁻
Reagents and conditions: Ethanolic potassium hydroxide and heat.
The base removes a hydrogen atom while the halide leaves, forming a carbon–carbon double bond.
How to distinguish the two reactions
The reaction conditions are essential:
- Aqueous hydroxide favours substitution to form an alcohol.
- Ethanolic hydroxide with heat favours elimination to form an alkene.
These are useful general rules for standard examination questions, although the precise outcome can depend on the halogenoalkane’s structure and other conditions.
5. Alcohols: Oxidation and Elimination
Alcohol reactions are frequently used in multi-step synthesis questions. You should know how primary, secondary and tertiary alcohols behave.
Oxidation of primary alcohols
A primary alcohol can be oxidised to an aldehyde or a carboxylic acid.
Primary alcohol → aldehyde → carboxylic acid
For example:
Ethanol → ethanal → ethanoic acid
Use acidified potassium dichromate(VI) as the oxidising agent.
- To obtain an aldehyde, heat gently and distil the aldehyde as it forms.
- To obtain a carboxylic acid, heat under reflux with excess oxidising agent.
The distinction matters because reflux allows the volatile aldehyde to remain in the reaction mixture and undergo further oxidation.
Oxidation of secondary alcohols
A secondary alcohol is oxidised to a ketone.
Propan-2-ol → propanone
Secondary alcohols are not normally oxidised to ketones and then further oxidised under these standard conditions in the same way that aldehydes are oxidised to carboxylic acids.
Tertiary alcohols
Tertiary alcohols resist oxidation by acidified potassium dichromate(VI) under ordinary A Level conditions.
Dehydration: Alcohol to alkene
Alcohols can also lose water to form alkenes.
Example:
Ethanol → ethene + water
Reagents and conditions: A suitable acid catalyst, such as concentrated sulfuric acid or phosphoric acid, and heat.
This is an elimination reaction because a small molecule, water, is removed from the organic compound.
6. Aldehydes and Ketones: Reduction and Identification
Aldehydes and ketones contain the carbonyl group, C=O. Both can undergo reduction using sodium borohydride.
Reduction reactions
Aldehyde → primary alcohol
Ketone → secondary alcohol
For example:
Ethanal → ethanol
Propanone → propan-2-ol
Reagent: Sodium borohydride, NaBH₄, in a suitable aqueous medium.
These reactions are examples of nucleophilic addition. In the mechanism, hydride attacks the partially positive carbon atom of the carbonyl group, followed by protonation.
Oxidation tests
Aldehydes can be oxidised to carboxylic acids, whereas ketones do not normally give the same positive results with the standard aldehyde tests.
- Tollens’ reagent: an aldehyde produces a silver mirror under suitable conditions.
- Fehling’s solution: an aldehyde typically produces a brick-red precipitate on warming.
- Ketones generally give negative results in these tests.
Learn both the observation and the chemical reason behind it.
7. Carboxylic Acids, Esters and Acyl Derivatives
Carboxylic acids contain the –COOH functional group. Their reactions are important for preparing esters and understanding organic synthesis.
Esterification
Carboxylic acid + alcohol ⇌ ester + water
Example:
Ethanoic acid + ethanol ⇌ ethyl ethanoate + water
Conditions: Concentrated sulfuric acid catalyst and heating.
Esters often have characteristic fruity smells and are used in flavourings, fragrances and solvents.
Reactions of acyl chlorides
Acyl chlorides are reactive compounds that undergo nucleophilic addition–elimination.
| Reactant | Organic product |
|---|---|
| Water | Carboxylic acid |
| Alcohol | Ester |
| Ammonia | Primary amide |
| Primary amine | N-substituted amide |
For example, ethanoyl chloride reacts with ethanol to form ethyl ethanoate and hydrogen chloride.
These reactions are useful in questions asking you to select a reagent that introduces a particular functional group.
8. Nitriles and Amines: Extending the Reaction Map
Nitriles provide an important route to compounds containing additional carbon atoms.
Halogenoalkane to nitrile
A halogenoalkane reacts with cyanide ions to form a nitrile.
Example:
CH₃CH₂Br + CN⁻ → CH₃CH₂CN + Br⁻
Conditions: Potassium cyanide in ethanol, heated under reflux.
The nitrile product contains one more carbon atom than the original halogenoalkane because the carbon in the cyanide ion becomes part of the carbon chain.
Nitrile to carboxylic acid
Nitriles can be hydrolysed by heating with dilute acid or aqueous alkali. Acidification may be required when hydrolysis is performed under alkaline conditions.
Preparing amines
Primary amines can be prepared by reducing nitriles or by reacting halogenoalkanes with ammonia under suitable conditions.
Ammonia acts as a nucleophile in substitution reactions with halogenoalkanes. Further substitution can occur, so the reaction can produce a mixture of amines and ammonium salts.
Always check the specified reagent and conditions before writing the final product.
9. Benzene: Electrophilic Substitution
Benzene behaves differently from ordinary alkenes because its delocalised pi-electron system provides additional stability.
Instead of readily undergoing addition reactions that disrupt this system, benzene commonly undergoes electrophilic substitution.
Nitration of benzene
Benzene → nitrobenzene
Reagents: Concentrated nitric acid and concentrated sulfuric acid.
Conditions: Warm carefully under the conditions specified by your course.
Sulfuric acid helps generate the nitronium ion, NO₂⁺, which acts as the electrophile.
Other aromatic reactions in A Level Chemistry can include halogenation and Friedel–Crafts reactions, depending on the specification.
10. How to Solve Multi-Step Organic Synthesis Questions
Organic synthesis questions test whether you can connect several reactions rather than recall individual equations.
Consider the following route:
Bromoethane → ethanol → ethanoic acid → ethyl ethanoate
Step 1: Bromoethane to ethanol
Use aqueous sodium hydroxide and heat to carry out nucleophilic substitution.
Step 2: Ethanol to ethanoic acid
Use acidified potassium dichromate(VI), heating under reflux with excess oxidising agent.
Step 3: Ethanoic acid to ethyl ethanoate
React ethanoic acid with ethanol in the presence of concentrated sulfuric acid and heat.
This example illustrates a practical way to plan a synthesis:
- Identify the functional group in the starting compound.
- Identify the functional group required in the product.
- Work backwards if the final product is unfamiliar.
- Select a reaction that changes the functional group appropriately.
- Write the reagent and conditions above each reaction arrow.
- Check the carbon skeleton and ensure that the final structure is correct.
The final step is important: a reaction pathway may contain chemically valid transformations but still produce the wrong number of carbon atoms or the wrong structural isomer.
11. Common A Level Organic Chemistry Exam Mistakes
Even when students remember the correct reaction, they can lose marks through incomplete answers.
Confusing aqueous and ethanolic hydroxide: These conditions can lead to different major products.
Forgetting distillation versus reflux: The apparatus affects whether a primary alcohol is oxidised mainly to an aldehyde or further to a carboxylic acid.
Writing incomplete mechanisms: Curly arrows should start from a lone pair or a covalent bond and point towards where the electron pair moves.
Ignoring carbon-chain changes: Converting a halogenoalkane into a nitrile adds one carbon atom to the chain.
Learning products without reagents: You need to know the complete transformation, including the conditions required.
Memorising without practising: Apply each reaction to unfamiliar structures and past-paper-style problems.
12. Frequently Asked Questions
What are the most important organic reactions in A Level Chemistry?
Focus on alkene addition, halogenoalkane substitution and elimination, alcohol oxidation and dehydration, carbonyl reduction, esterification, acyl chloride reactions and multi-step organic synthesis. The exact list depends on your exam board.
How can I memorise A Level organic chemistry reactions?
Create a reaction map organised by functional group. Use active recall to test the starting compound, reagent, conditions and product separately. Then practise drawing complete pathways without looking at your notes.
Do AQA, OCR and Edexcel have the same organic chemistry reactions?
They share many core concepts, but the required reactions, mechanisms, depth and assessment expectations differ. Always use the specification and data booklet for your own exam board.
How do I improve in organic chemistry exam questions?
Practise identifying functional groups, writing balanced equations, drawing mechanisms and planning multi-step synthesis. Review your mistakes and identify whether the problem was the reagent, conditions, mechanism or product structure.
When should I get help from an A Level Chemistry tutor?
If you repeatedly struggle to connect reactions, select suitable conditions or solve unfamiliar synthesis questions, working with an A Level Chemistry tutor can help you identify gaps in your understanding and practise the reasoning required for exam questions.
Final Thoughts
The most effective way to learn A Level Organic Chemistry is to see it as a connected system of reactions. Once you understand how alkanes, alkenes, halogenoalkanes, alcohols, carbonyl compounds, carboxylic acids and other functional groups interconvert, multi-step synthesis becomes easier to approach.
Keep this reaction map alongside your revision notes, practise applying the reactions to unfamiliar compounds, and check every transformation against your exam-board specification.
If you need additional support with organic mechanisms, reaction conditions or exam-style synthesis questions, explore Bright Mind Tutors’ A Level Chemistry tutoring to find support with your Chemistry studies.
For further specification-specific revision, refer to the official AQA A Level Chemistry specification or the relevant OCR or Pearson Edexcel specification.