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Edexcel A-Level Chemistry A2 18.3 Why Benzene Is Resistant to Bromination Compared to Alkenes in Terms of Delocalisation of Bonds in Benzene Compared Questions

The direct evidence asks for comparison: benzene needs a catalyst and undergoes substitution, unlike alkenes where localised π electrons support addition.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Compare benzene substitution with cyclohexene addition when reacting with bromine.
  • Explain benzene’s lower bromination reactivity through delocalised π electrons.
  • Contrast benzene and phenol bromination conditions when the comparison is requested.

Edexcel A-Level Chemistry A2 18.3 Why Benzene Is Resistant to Bromination Compared to Alkenes in Terms of Delocalisation of Bonds in Benzene Compared Questions question 1

[Maximum number: 2]

This question is about benzene, C_6 H_6, a colourless liquid first isolated in 1825, and some related compounds.

Three C_6 H_6 structures proposed in the 1860 s are shown.

Table for Question Edexcel A-Level Chemistry A2 18.3 Why Benzene Is Resistant to Bromination Compared to Alkenes in Terms of Delocalisation of Bonds in Benzene Compared Questions question 1 — Edexcel A-Level Chemistry A2

The delocalised model for the structure of benzene has been accepted since the 1930s following the study of its X-ray diffraction pattern and the understanding of electron delocalisation in bonding theory.

The Dewar and Ladenburg structures have since been isolated as stable compounds but there is no compound with the Kekulé structure.

Figure for Question Edexcel A-Level Chemistry A2 18.3 Why Benzene Is Resistant to Bromination Compared to Alkenes in Terms of Delocalisation of Bonds in Benzene Compared Questions question 1 — Edexcel A-Level Chemistry A2

Describe a chemical test, including the result, that could distinguish the Dewar structure from benzene.

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