Structure of Benzene

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What was the Kekule model of benzene?
A ring with 3 double bonds constantly flipping between 2 different isomers.
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What were the problems with Kekule's structure of benzene?
Unreactive compared to alkenes. Bond lengths are all the same, not different. Enthalpy change of hydrogenation is much lower than expected.
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What type of reaction takes place between alkenes and bromine?
Nucleophilic Substitution
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What is the enthalpy change of hydrogentation of cyclohexane?
-120kJ per mol
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What is the expected and actual enthalpy change of hydrogenation?
Expected: -360kJ per mol Actual: -208kJ per mol
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What is the delocalisation or resonance energy of benzene?
152 kJ per mol (benzene is 152kJ per mol more stable than the Kekule structure)
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What are the lengths of a C=C and a C-C bond
C=C 0.134nm C-C 0.153nm
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What technique was used to show all the bond lengths in benzene are the same?
X-ray studies showed that benzene has a regular hexagon shape.
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Card 2

Front

What were the problems with Kekule's structure of benzene?

Back

Unreactive compared to alkenes. Bond lengths are all the same, not different. Enthalpy change of hydrogenation is much lower than expected.

Card 3

Front

What type of reaction takes place between alkenes and bromine?

Back

Preview of the front of card 3

Card 4

Front

What is the enthalpy change of hydrogentation of cyclohexane?

Back

Preview of the front of card 4

Card 5

Front

What is the expected and actual enthalpy change of hydrogenation?

Back

Preview of the front of card 5
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