‹ Chemistry simulationsChemistry · A Level 9701 · 30 ArenesFive simulations covering Topic 30: the delocalised ring of benzene built from six p orbitals in 3D, electrophilic substitution stepped through with curly arrows and the Wheland intermediate for nitration and bromination, a reagent bench for nitration, halogenation and the Friedel-Crafts reactions, methylbenzene reacting at the ring or on the side chain depending on the conditions, and the directing effects that decide where a second group goes.
Each carbon in benzene uses three sp² orbitals to make sigma bonds, all in one flat plane at 120°. That leaves one p orbital per carbon pointing straight up and down. Switch on the p orbitals, then let them overlap sideways and watch the six electrons spread into a ring above and below the plane.
The pi cloud above the ring is rich in electrons, so benzene attacks electrophiles. Choose nitration or bromination and step through it: make the electrophile, let the ring attack it, see the horseshoe intermediate with its delocalised positive charge, then lose H⁺ to get the ring back.
Every electrophilic substitution of benzene follows the same pattern: a catalyst makes a strong electrophile from a reagent that is not electrophilic enough by itself. Pick a reagent set, see the conditions, the electrophile and the product, then try leaving the catalyst out.
Methylbenzene has two places to react: the ring and the methyl group. The conditions decide which. UV light with chlorine attacks the side chain by free radicals; a halogen carrier in the dark attacks the ring by electrophiles; hot alkaline potassium manganate(VII) oxidises the side chain to a carboxylic acid.
A group already on the ring decides where the next one goes. Electron-donating groups push the next electrophile to positions 2, 4 and 6; electron-withdrawing groups push it to 3 and 5. Choose a group, then choose a position to attack and see whether the intermediate can cope with it.
Five interactive simulations for Cambridge A Level Chemistry 9701 topic 30 Arenes: the sigma skeleton, p orbitals and pi doughnut of benzene in 3D with bond lengths and the 150 kJ per mole delocalisation energy, electrophilic substitution of benzene by NO2+ and Br+ stepped through with curly arrows and the horseshoe intermediate, a reagent bench for nitration, bromination and Friedel-Crafts alkylation and acylation with the electrophile each one generates, methylbenzene showing side-chain free-radical substitution in UV light against ring substitution with a halogen carrier plus oxidation to benzoic acid, and a 2,4-directing against 3-directing explorer that names the product of a second nitration.
Five simulations covering Topic 30: the delocalised ring of benzene built from six p orbitals in 3D, electrophilic substitution stepped through with curly arrows and the Wheland intermediate for nitration and bromination, a reagent bench for nitration, halogenation and the Friedel-Crafts reactions, methylbenzene reacting at the ring or on the side chain depending on the conditions, and the directing effects that decide where a second group goes.
Arenes is a free, browser-based simulation for Cambridge International AS & A Level Chemistry 9701 (topic 30 Hydrocarbons). The course is assessed in Paper 1 (Multiple Choice (AS)), Paper 2 (AS Structured), Paper 3 (Advanced Practical), Paper 4 (A Level Structured), Paper 5 (Planning, Analysis, Evaluation). Syllabus for examination in 2025-2027. There are 5 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.
Full syllabus map: A Level Chemistry 9701 topic 30.
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