How is Unit 4 examined in WJEC A-Level Chemistry?

Unit 4 is an A2 written paper at higher demand. Expect mechanism questions on electrophilic substitution and nucleophilic addition, the distinguishing tests for functional groups, explanations of optical isomerism and the acidity of phenol, multi-step synthesis routes, and the interpretation of mass, infrared and NMR spectra. A calculator and a periodic table are provided.

What is the most predictable extended question in Unit 4?

Structure determination from spectra. Be ready to combine the molecular mass and fragments from mass spectrometry, the functional groups from infrared, and the hydrogen environments, integration and splitting from proton NMR to deduce a complete structure. This synoptic skill is tested almost every year.

How should I revise the organic reactions?

Build a single reaction map linking every functional group by reagents, conditions, mechanism and product. Drill the distinguishing tests (Tollens', Fehling's, bromine water and iron(III) chloride) and the mechanisms of electrophilic substitution, nucleophilic addition and substitution, so you can plan a synthesis in either direction.

Why is benzene so important in Unit 4?

Benzene's delocalised structure makes it stable and explains why it undergoes electrophilic substitution rather than addition. Aromatic chemistry, including nitration and the comparison with alkenes, recurs through the unit and links to the phenol chemistry and to structure determination.

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WJEC A-Level Chemistry Unit 4 Organic Chemistry and Analysis: a deep dive on stereoisomerism, aromaticity, the functional groups, synthesis and spectroscopy

Q: What does Unit 4 of WJEC A-Level Chemistry cover?

Unit 4, Organic Chemistry and Analysis, is the final A2 unit. It covers stereoisomerism (E-Z and optical), aromaticity and the reactions of benzene, alcohols and phenols, aldehydes and ketones, carboxylic acids and their derivatives, amines and amino acids, the planning of multi-step organic synthesis with purification, and the analytical techniques of mass spectrometry, infrared, NMR and chromatography.

A deep-dive WJEC A-Level Chemistry guide to Unit 4. Covers stereoisomerism, aromaticity and benzene, alcohols and phenols, aldehydes and ketones, carboxylic acids and their derivatives, amines and amino acids, organic synthesis and analysis, and spectroscopy and chromatography.

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What Unit 4 actually demands
Isomerism and aromaticity
The functional groups
Synthesis and analysis
Check your knowledge

What Unit 4 actually demands

Unit 4 completes the course with advanced organic chemistry and analysis. Examiners want fluent mechanism work, the distinguishing tests at your fingertips, confident synthesis planning, and the ability to deduce a structure from combined spectra. The reaction map you build here is the single most useful revision tool.

This guide ties together the eight topics of the unit, each with a matching dot-point page.

Isomerism and aromaticity

Stereoisomerism covers E-Z isomerism about a double bond and optical isomerism at a chiral centre, with enantiomers rotating plane-polarised light. Aromaticity explains benzene's delocalised stability and its electrophilic substitution reactions such as nitration.

The functional groups

Alcohols and phenols, aldehydes and ketones, carboxylic acids and their derivatives, and amines and amino acids each have characteristic reactions and tests. Phenol's acidity, the carbonyl tests, ester formation and hydrolysis, and amino-acid zwitterions and peptide bonds are all examined.

Synthesis and analysis

Organic synthesis plans multi-step routes through functional-group interconversions, with recrystallisation and melting-point checks for purity. Analysis combines mass spectrometry, infrared, NMR and chromatography to identify unknown compounds.

Check your knowledge

Attempt these under timed conditions, then check against the solutions.

Explain what gives a carbon atom a chiral centre. (1 mark)
Explain why benzene undergoes substitution rather than addition. (2 marks)
Explain why phenol is more acidic than ethanol. (2 marks)
Describe a test to distinguish an aldehyde from a ketone. (2 marks)
Give the conditions for esterification of a carboxylic acid. (1 mark)
Explain why amines are basic. (2 marks)
Describe how to purify an impure organic solid. (2 marks)
State what the molecular ion peak in a mass spectrum gives. (1 mark)

Sources & how we know this

WJEC A-level Chemistry specification — WJEC (2015)