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H2 Chemistry 9729 · Nov 2023Chemistry (H2)Paper 1Most challenging

Paper 1 Q20 — Benzene has no alternating bonds

Aromaticity — delocalised π system vs the Kekulé alternating-bond picture

What the examiners said

“The most common incorrect choice, option D, highlights a popular misconception that a benzene molecule has alternating double and single bonds in addition to the ring of delocalised electrons.”

Try the question (reconstruction)

Which statement about the bonding in benzene, C₆H₆, is correct?
Examiner report: “The popular misconception adds alternating double/single bonds on top of the delocalised ring.”

Explore — Kekulé vs the real benzene

Switch between the Kekulé drawing (alternating bonds) and the delocalised model. Compare the predicted bond lengths — experiment matches the delocalised, equal-length picture.

The single strongest evidence: all six C–C bond lengths are equal — impossible if the bonds alternated.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H2 Chemistry 9729 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org