Benzene Chemistry

Question 0

Benzene’s stability Is due to…

Answer 0

delocalised pi Structure
All electrons in p orbitals on parallel carbon atoms
Allows overlap
Therefore there is a high electron density above and below
Makes benzene sucesptible to electrophillic attack

Question 1

Enthalpy of Hydrogentation

Answer 1

Enthalpy change when 1 mole of c=c double bonds are reduced to single bonds using gaseous hydrogen

Question 2

Combustion of Benzene

Answer 2

Complete: C6H6 + 7 1/2O2 –> 6CO2 + 3H2O

Incomplete: C6H6 + 1 1/2O2 –> 6C + 3H2O

Question 3

Hydrogenation

Answer 3

Randy Nickel (large surface area)
200'C

Turns benzene into cyclohexane

Question 4

Free radical addition of chlorine

Answer 4

UV light - to create radicals
Cl is bubbled through boiling benzene

NB if Methyl group present then it take precedent and reacts with chlorine

Question 5

Halogentation

Answer 5

Only happens in light–> free radicals formed from UV

Bromine
Warm Al/ Fe to make FeBr3/ AlBr3

*bromo compounds more synthetically useful as they are more reactive

Question 6

Nitration of Benzene

Answer 6

Conc H2SO4 and HNO3
Reflux, 55’C

*at temps higher than 55’C, a second group is added

Question 7

Freidal - Crafts ( alkylation)

Answer 7

Haloalkane RCl ( DRY otherwise complex ion forms)
Catalyst AlCl3

Diffucult to stop therefore formation of multiple products

Question 8

Acylation of Benzene

Answer 8

Acid Chloride

DRY AlCl3 or FeCl3

Question 9

Sulphonation of Benzene

Answer 9

SO3 (H2S2O7 from oleum) –> 40’c 20-30mins

OR

conc H2SO4 –> reflux for many hours

Question 10

Electron donating

Answer 10

-OH, -CH3

Activates ring
Increases electron density
Substitution is therefore easier

Question 11

Electron withdrawing

Answer 11

-NO2

Deactivates ring
Electron density decreases