arenes

Question 1

what are the physical properties of benzene

Answer 1

1. insoluble in water - consider the type of of bonds they form with polar water molecules vs the strong hydrogen bonds between water molecules
2. mp increases with increase in Mr as id-id int become stronger with more electrons

Question 2

what do benzene react with

Answer 2

1. NaOH or KOH both aq to form alcohol - anhydrous FeCl3 at rtp
2. RX to undergo Friedel-crafts alkylation - anhydrous AlCl3 at rtp
3. nitric acid to form nitrobenzene - conc H2SO4 and conc HNO3 both aq and heat at 60 degrees
4. addition of hydrogen to break the bring - H2 gas plus ni catalyst at high temp and pressure

Question 3

what type of mechanism does benzene undergo and how does it differ from alkenes

Answer 3

• electrophilic sub not addition in order to preserve its ring structure
• delocalisation of pi electrons renders the benzene ring less nucleophilic than alkenes so they are only attacked by strong electrophiles

Question 4

how does the electrophilic sub mechanism work

Answer 4

1. Generate strong electrophile with the use of acid catalyst eg H2SO4 or FeCl3
2. Electrophilic attack forming intermediate ( not full circle with a plus opp where the electrophile attacks)
3. Proton loss by intermediate regenerating catalyst

Question 5

why does further alkylation of benzene occur more readily

Answer 5

The existing alkyl group exerts an electron donating inducting effect which increases the electron density of the benzene ring.
This makes electrophilic attack much easier

Question 6

difference in reactions between methylbenzene and benzene

Answer 6

Nitration only requires heating at 30 degrees but needs the same catalyst H2SO4
Able to be oxidised to aldehydes with weak OA and carboxylic acids if there is a benzylic H and strong OA is used