3.10 Aromatic

Question 1

The rule of cyclics

Answer 1

All benzene are cyclic compounds; but not all cyclic compounds are benzene

Question 2

What is benzene?

Answer 2

C6H6
Flat hexagon of carbon atoms
Delocalised rings of electrons

Question 3

What is the thermochemical evidence of Benzene structure?

Answer 3

Cyclohexene + H2 → ∆H -120
Expected + H2 → ∆H -360
Benzene + H2 → ∆H -208

so we learn that benzene is 152 kJ more stable than predicted due to delocalised field

Question 4

What is delocalisation of Benzene?

Answer 4

overlapping of electron density

sandwiched between 2 rings

Question 5

How does bond length affect stability?

Answer 5

c=c is most stable 0.134
(B) c-c is 0.140
c-c is 0.154, the weakest

Question 6

What is electrophilic substitution?

AROMATIC

Answer 6

Using benzene delocalised ring to donate electrons

Question 7

How to prepare the Nitration of Benzene species?

Answer 7

H2SO4 + HNO3 → H2NO3+ + HSO4-

H2NO3+ → NO2+ +H2O

We use NO2+

H2SO4 is a catalyst as it is replenished at the end by H+ from benzene

Question 8

What is nitrobenzene used for?

Answer 8

TNT
Bombs
Dyes

Question 9

What is Friedel Craft acylation?

Answer 9

Adding a carbonyl group to benzene, with AlCl3 as a catalyst

RCOCl + AlCl3 → RCO+ + AlCl4-

Question 10

Why does electrophilic substitution occur on benzene?

Answer 10

The delocalised repels nucleophiles

If addition occurred the ring would have to break which requires a lot of energy