Aromatics Flashcards
What was wrong with Kerkule’s idea for the structure of benzene?
4
- It should show addition reactions
- Should give rise to Z isomeric di-substituted compounds
- Double bonds are shorter so it would be an irregular hexagon
- Would expect increased hydrogenation
What was Kerkule’s suggestion for the structure of benzene?
Hexagonal
Alternating single and double bonds
What did Kerkule suggest to account for the problems in his theory and what theory did it lead to?
3
- Suggested Benzene switched structures (placements of double bonds) in rapid equilibrium
- Led to the idea of resonance between the two structures
- Thought the structure to be an average/ resonance hybrid between the two
What is the formula of benzene?
C6H6
What happens when benzene is burnt?
Smoky flame
Unburnt carbon
What is the shape of benzene?
1
-Flat regular hexagon of C atoms, each one bonded to one H atom
What is the bonding and structure of benzene?
5
- Each C has three covalent bonds
- Fourth electron sits in pi orbital
- The pi orbitals overlap
- Leads to region of electron density above and below
- Means very stable
- (delocalised charge)
What are the physical properties of benzene?
4
- High melting point
- Non-polar
- Doesn’t dissolve with water
- Dissolves with hydrocarbons and non-polar solvents
Why does benzene have a high melting point?
1
The flat hexagonal molecules pack together well in solid state
How does benzene react?
(why electrophilic substitution?)
4
- The ring of high electron density / delocalised charge
- Means that it is attacked by electrophiles
- Benzene is very stable so needs delocalisation energy to break the ring
- The ring is almost always intact therefore electrophilic substitution
How does benzene undergo further substitution?
How do the groups on benzene affect further substitution?
2
- Some groups release electrons towards the ring which makes it more susceptible to electrophilic substitution
- Some groups withdraw electrons towards the ring which makes it less susceptible to electrophilic substitution
How do the groups on benzene withdrawing/releasing electrons affect further substitution?
3
- This directs further substitution to specific positions
- If electrons are released, substitution on 2,4,6
- If electrons are withdrawn, substitution on 3,5
What does nitration produce?
2
Aromatic amines - used for dyes
Explosives like TNT
What are the conditions for nitration?
1
50*C
What reagents are used in nitration?
2
Conc. HNO3
Conc. H2SO4
