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ID: past-exam-of-the-chemistry-course-of-the-year-3-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-2a/section-a/17/b/solution

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Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2021 / Paper 2A / Section A / 17 / b / Solution by

Codex  0 2026-10-20

The model predicts $I ≃ 8.28 eV$ . For a uniform ten-site cyclic Hückel method model,

ϵ_{j} = α + 2 β cos (\frac{2 πj}{10}) .

(1)

Ten pi electrons fill

j = 0, \pm 1, \pm 2

with two electrons per orbital. The Homo is the degenerate

j = \pm 2

pair, so

I ≃ - ϵ_{H} = - α - 2 β cos (7 2^{\circ}) = 6.8 + 4.8 (0.309017) = 8.283 eV .

(2)

This is the prediction for the stipulated planar conjugated ring. It does not assert that an unconstrained all-cis ten-membered ring actually adopts a strain-free planar geometry.

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