Module 6

Question 1

Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekule model and the delocalised model of benzene.

Answer 1

Both have sideways overlap of p orbitals

They both havre a pi bond above and below the bonding carbon atoms

Kekule has alternating pi bonds and delocalised has pi ring system

Question 2

Describe two pieces of evidence to support the delocalised model of benzene.

Answer 2

The c-c bond length are the same
Enthalpy change of hydrogenation is less exothermic than expected
Benzene is less reactive than alkenes

Question 3

Draw the mechanism and any equations of the Electrophilic substitution of the nitration of benzene.

Answer 3

Equation for formation: HNO3 +H2SO4 —> NO2+ + HSO4- + H2O

Drawn mechanism

H+ + HSO4- —> H2SO4

Question 4

Draw the mechanism and equations for the Electrophilic substitution of the halogenation of benzene.

Answer 4

Equation for formation:
AlCl3 + Cl2 —> AlCl4- + Cl+
Or
FeBr3 + Br2 —> FeBr4- + Br+

Drawn mechanism

H+ + AlCl4- —> AlCl3 + HCl
Vice versa

Question 5

Describe the acidity of phenols.

Answer 5

They are weakly acidic
They are weaker acids than carboxylic acids
They both will react with sodium metal and sodium hydroxide but only carboxylic acid will react with sodium carbonate as phenol is not strong enough an acid to react with