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- 1What did Kekule propose was the structure of benzene?He suggested that benzene has 3 double bonds.
- 2Why were there problems with this structure?If benzene had double bonds it would undergo addition reactions, but it did not. Benzene does not decolourise when added to bromine.
The enthalpy of hydrogenation of cyclohexene, with one double bond, is -120 Kjmol-1. Benzene should be -360 but it is only -208.
Benzene is more stable than Kekule suspected. - 3Describe the structure of benzeneBenzene has a hexagonal planar structure.
Each of the 6 carbon atoms have a spare p-orbital.
The spare p- orbitals overlap sideways to form pi bonds.
Benzene has thermodynamic stability due to the delocalised electrons from the spare p- orbitals. - 4How does benzene maintain the delocalisation of electrons?It undergoes electrophilic substitution reactions rather than addition.
As the pi bonds have a high electron density, benzene is attractive to electrophiles. - 5What is the equation for the nitration of benzene?C6H6+HNO3----> C6H5NO2+H2O
- 6What are the reagents and conditions in this reaction?The reagents are concentrated H2SO4 and HNO3. These make up the nitrating mixture.
A temperature lower than 55 degrees Celsius.
Fractional distillation. - 7What is the equation for the generation of the electrophile (nitronium ion)?HNO3+H2SO4----> NO2+ HSO4-+H2O
- 8What is the equation for the chlorination of benzene?C6H6+CL2----> C6H5CL+ HCL
- 9What are the reagents?CL2 and a Halogen carrier (FE, AL)
- 10Write an equation for th generation of the electrophile.CL2+FECL3----> CL+ + ALCL4-
CL2+ ALCL3----> CL+ + FECL4- - 11What is the role of the halogen carrier?To act as a catalyst.
- 12Compare the reactivity of alkenes with benzene.The double bond of the alkene readily reacts with electriphiles.
Due to the ring of delocalisation in benzene, it is less reactive than alkenes.
The ring of delocalised electrons is not easily disrupted so the activation energy of benzene is higher than alkenes.
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- Fichas sobre Sin título, creado por georgialula4 el 31/12/2015.
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- georgialula4 · dic 2015
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- 22 mar 2016
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