Benzene

Question 1

Structure of benzene

Answer 1

planar molecule- C6H6, Bond angle of 120 degrees
1 unpaired electron on the P orbital of each carbon, perpendicular to the plane of the ring
Form a delocalised Pi system above and below the molecule

Question 2

Why is the enthalpy of hydrogenation of Benzene lower than predicted based on its theoretical structure with 3 double bonds?

Answer 2

Should be 3x the enthalpy of cyclohexene
Actually lower than this
Electrons not arranged in double bonds, delocalised, increase in stability-

Question 3

why does the enthalpy of hydrogenation of cyclohex-1,3-diene differ from that of cyclohex-1,4-diene?

Answer 3

In 1,3- some delocalisation with the Pi electrons relativel close together so they overlap, less negative hydrogenation

In 1,4 would not have delocalisation because the Pi electrons are too far away from eachother- don’t overla, more negative hydrogenation

Question 4

Formation of electrophile in electrophilic substitution of NO2 +

Answer 4

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

Question 5

Types of reactions of benzene

Answer 5

Electrophilic substitution of NO2 +
Electrophilic substitution of Acyl Chlorides (Friedel Craft acylation)
Reduction of Nitrobenzene to aromatic amine

Question 6

conditions for electrophilic substitution of NO2 +

Answer 6

Conc HNO3 (NO2 +)
H2SO4 catalyst

Question 7

conditions for friedel craft acylation

Answer 7

Acyl chloride
AlCl3 catalyst
heat under reflux 50 degrees

Question 8

conditions for reduction of nitrobenzene

Answer 8

Sn and HCl or Fe and HCl
Heating
ALTERNATIVE: H2 with Ni catalyst