Benzene

Question 1

Structure of benzene

Answer 1

1. C has one extra electron in p orbital
2. p orbitals overlap
3. cloud negative charge above and below carbon ring
4. electrons are delocalised
5. ring is planar
6. bond angle 120°
7. carbon bonds are equal length and strength

Question 2

Stability of benzene

Answer 2

1. low electron density
2. p electrons delocalised
3. need to be attacked by electrophile

Question 3

Evidence for delocalised structure

Answer 3

1. No decolourisation when reacted with bromine water
2. hydrogenation is less exothermic -208 then Kekule structure -360
3. carbon bonds are same length and structure

Question 4

Benzene to nitrobenzene

Answer 4

Reagents: HNO3
Conditions: c.H2SO4, 55°C
Mechanism: electrophilic substitution / nitration

Question 5

Nitration catalyst reactions

Answer 5

2H2SO4 + HNO3 -> HSO4- + H3O+ + NO2+

H+ + HSO4- -> H2SO4

Question 6

Benzene to halo-benzene

Answer 6

Reagents: X2
Conditions: AlX3(s), reflux
Mechanism: electrophilic substitution / halogenation

Question 7

Benzene to alkyl-benzene

Answer 7

Reagents: alkyl chloride
Conditions: AlCl3
Mechanism: electrophilic substitution / alkylation

Question 8

Benzene to acyl-benzene

Answer 8

Reagents: acyl chloride
Conditions: AlCl3
Mechanism: electrophilic substitution / alkylation

Question 9

Cyclohexene vs benzene

Answer 9

1. high electron density C=C
2. electrons are localised
3. induces a dipole
4. benzene low electron density
5. p electrons delocalised
6. can’t induce a dipole