The stucture of benzene

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  • Created by: mgb495
  • Created on: 02-11-13 17:45
What was the problem with Kekule's original structure?
It did not explain benzene's low chemical reaction because benzene would react in a similar way to alkenes and would react with bromine water if C=C bonds were present.
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What was Kekule's refined structure off benzene?
He suggested that benzene had 2 forms that were in rapid equilibrium. The forms differ by the position of the double bonds.
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What is the true length of the C-C bonds in benzene and how was this discovered?
0.139nm and this was determined by x-ray crystallography. This length is between that of C-C and C=C bonds.
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What is the expected enthalpy change of hydrogenation of benzene and why?
-360kJ mol-1 because the enthalpy change of hydrogenation of cyclohexene which has one C=C bond is -120kJ mol -1. It would be expected that Kekule's structure has an enthalpy change 3 times that.
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What is the actual enthalpy change of benzene and why is it different to Kekule's proposed structure?
-208kJ mol-1 because the actual structure is more stable than Kekule's structure.
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What would you expect to see if cyclohexene reacted with benzene and what is the equation for this?
The bromine would be decolourised. C6H10 + Br2 --> C6H10Br2
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What type of reaction takes place between alkenes and bromine?
Electrophilic addition
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Card 2

Front

What was Kekule's refined structure off benzene?

Back

He suggested that benzene had 2 forms that were in rapid equilibrium. The forms differ by the position of the double bonds.

Card 3

Front

What is the true length of the C-C bonds in benzene and how was this discovered?

Back

Preview of the front of card 3

Card 4

Front

What is the expected enthalpy change of hydrogenation of benzene and why?

Back

Preview of the front of card 4

Card 5

Front

What is the actual enthalpy change of benzene and why is it different to Kekule's proposed structure?

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