OCR A-Level Chemistry A: Module 6 (Organic chemistry and analysis) overview

What this module demands

Module 6 of OCR A-Level Chemistry A completes the organic course and brings together the analytical techniques used to confirm structure. It adds the chemistry of the benzene ring, the carbonyl group, carboxylic acids and their derivatives, and nitrogen-containing compounds and polymers, then equips you to deduce structures from chromatography and NMR. It rewards confident mechanism work, precise recall of reagents, conditions and tests, and careful interpretation of spectra.

This guide walks through Module 6 in specification order and sets out the exam patterns OCR repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Aromatics, carbonyls, acids and esters (6.1)

Aromatic compounds (6.1.1) establish the delocalised structure of benzene (which explains its stability and its preference for substitution over addition) and the electrophilic substitution reactions: nitration, halogenation and Friedel-Crafts acylation.

Carbonyl compounds (6.1.2) cover aldehydes and ketones: their oxidation (aldehydes only) and reduction, nucleophilic addition with hydrogen cyanide, and the tests that distinguish them (2,4-DNPH for any carbonyl, Tollens' reagent and Fehling's solution for aldehydes).

Carboxylic acids and esters (6.1.3) cover the acidity of carboxylic acids, esterification, ester hydrolysis, and the more reactive acyl chlorides and acid anhydrides.

Nitrogen, polymers and synthesis (6.2)

Amines (6.2.1) act as bases (the nitrogen lone pair accepts a proton) and are made from haloalkanes or by reducing nitriles. Amino acids, amides and chirality (6.2.2) introduce zwitterions, the amide link, and optical isomerism (a chiral centre is a carbon with four different groups). Polyesters and polyamides (6.2.3) are condensation polymers. Carbon-carbon bond formation (6.2.4) uses nitriles to lengthen a chain, and organic synthesis (6.2.5) plans multi-step routes.

Analysis (6.3)

Chromatography (6.3.1) separates mixtures by thin-layer (TLC, with $R_f$ values) and gas chromatography (retention times). NMR spectroscopy (6.3.2) uses carbon-13 and proton NMR (chemical shift, integration and the n+1 splitting rule, with TMS as reference). Combined techniques (6.3.3) bring NMR, infrared, mass spectrometry and chemical tests together to identify unknowns.

How this module is examined

A typical OCR profile for Module 6:

• Mechanisms. Electrophilic substitution on benzene (nitration, Friedel-Crafts) and nucleophilic addition to carbonyls.
• Reagents, conditions and tests. Distinguishing aldehydes and ketones, making and hydrolysing esters, and acyl chloride reactions.
• Polymers and isomerism. Drawing condensation polymer repeat units and identifying optical isomers.
• Synthesis. Planning multi-step routes across Modules 4 and 6.
• Structure determination. Reading carbon-13 and proton NMR with integration and splitting, combined with infrared and mass spectra.

Check your knowledge

A mix of mechanism, recall and analysis across Module 6. Attempt them under timed conditions, then check against the solutions.

1. State why benzene undergoes substitution rather than addition. (2 marks)
2. Give the reagents and conditions for the nitration of benzene. (2 marks)
3. Name the reagent that gives a silver mirror with an aldehyde but not a ketone. (1 mark)
4. State the reagents and conditions to make an ester from a carboxylic acid and an alcohol. (2 marks)
5. State what the integration trace in a proton NMR spectrum tells you. (1 mark)
6. Apply the n+1 rule to predict the splitting of the $\text{CH}_3$ protons in $\text{CH}_3\text{CH}_2\text{Br}$. (2 marks)