Aromatic chemistry
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
The topic on one screen
- Benzene is a planar ring of six carbons; each carbon's p-orbital overlaps to form a delocalised ring of pi electrons above and below the plane.
- Evidence for delocalisation: all C-C bonds are equal length; the enthalpy of hydrogenation is less exothermic than the Kekulé model predicts (so benzene is more stable); it resists addition.
- Because the ring is electron-rich but stable, benzene reacts by electrophilic SUBSTITUTION (keeping the ring), not addition.
- Nitration: conc. HNO3 with conc. H2SO4 (catalyst); electrophile is the nitronium ion NO2+.
- Friedel-Crafts acylation: acyl chloride with an AlCl3 catalyst (a halogen carrier) to make an aromatic ketone.
- Nitrobenzene → phenylamine using tin and concentrated HCl (then NaOH); aromatic amines are used to MANUFACTURE dyes.
Where students actually lose marks
Common mistakes in drawing the nitration intermediate have been covered many times in past reports, yet keep recurring: show the positive intermediate with the horseshoe (partial ring) and the C bonded to both H and NO2, then H+ lost to restore the ring.
June 2024 Paper 2 examiner report (Q10.3)
Fewer than 10% scored the 'use of aromatic amines' mark because they said the amines are used AS dyes. The specification says they are used to MANUFACTURE dyes — the wording matters.
June 2024 Paper 2 examiner report (Q10.5)
On a familiar electrophilic substitution, a disappointing number could not write the equation and name the organic product. Practise the full equation, not just the mechanism arrows.
June 2022 Paper 2 examiner report (Q08.1)
Try it — exam-style
Give two pieces of evidence that benzene has a delocalised ring of electrons rather than three localised C=C double bonds.
Write an equation to show how the nitronium ion, NO2+, is generated from concentrated nitric acid and concentrated sulfuric acid.
In the nitration of benzene the electrophile NO2+ attacks the ring. Describe what happens next, including how the aromatic ring is restored.
State the reagents and conditions to convert nitrobenzene into phenylamine.
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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Stuck on aromatic chemistry?
Examiners flag the same nitration-intermediate error year after year — I make sure you draw it the way the mark scheme wants, and the first lesson is free.