Give two pieces of evidence that benzene has a delocalised ring of electrons rather than three localised C=C double bonds.
[2 marks]
Total for this question: 2
Chemistry
Aromatic chemistry
AQA 3.3.10
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
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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
Medium
ORIGINAL · after June 2024 Paper 2 Q10.1
Medium
ORIGINAL · after June 2022 Paper 2 Q08.2
Write an equation to show how the nitronium ion, NO2+, is generated from concentrated nitric acid and concentrated sulfuric acid.
[1 mark]
Total for this question: 1
Hard
ORIGINAL · after June 2024 Paper 2 Q10.3
In the nitration of benzene the electrophile NO2+ attacks the ring. Describe what happens next, including how the aromatic ring is restored.
[2 marks]
Total for this question: 2
Medium
ORIGINAL · after June 2024 Paper 2 Q10.4
State the reagents and conditions to convert nitrobenzene into phenylamine.
[2 marks]
Total for this question: 2
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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