Benzene

Question 1

Structure of benzene

Answer 1

• each c atom uses 3 electrons to form 3 sigma bonds with neighbours 2 carbons 1 hydrogen
• leaving extra electron in p-orbital
• p orbitals are perpendicular to carbon ring
• p orbital overlap
• electrons delocalised over entire molecule
• form circular clouds of negative charge (delocalised pi electrons free to move around) above and below the carbon chain

Question 2

Why benzene is stable

Answer 2

Charge is spread over larger region with delocalised electrons

Needs to be attacked by electrophile

Question 3

Electrophilic substitution

Answer 3

replaces hydrogen with electrophile

Question 4

Nitration

Answer 4

Reagents: conc H2SO4, conc HNO3
Conditions: 50-55 degrees

replaced hydrogen with NO2

Question 5

Sulphonation

Answer 5

Reagents: conc H2SO4
Conditions: reflux or 40 degrees

replace hydrogen with SO3H and produce water

Question 6

Alkylation

Answer 6

Reagent: halogenalkane
Conditions: catalyst AlCL3 or FeBr3

replace hydrogen with CnHn+1

Question 7

Alcylation

Answer 7

Reagent: acyl chlorides
Conditions: catalyst AlCl3

replace hydrogen with COR
produce HCl

Question 8

Fiedel Crafts reaction

Answer 8

AlCl3 forms an electrophile

Then substitution occurs

Then AlCl4- reforms halogen carrier to HCl

Question 9

Halogenation

Answer 9

Reagent: halogen

Conditions: FeCL3 or Alcl3 catalyst

replace H with halogen

Question 10

Kekule structure

Answer 10

Alternating single and double bonds in carbon ring

Question 11

Evidence for delocalised structure

Answer 11

1. Doesn’t decolourise when reacted with bromine water
2. Hydrogenation is less exothermic -208 then Kekule predicted -360
3. All C-C bonds are same length and structure