Aromatic Chemistry

Question 1

Benzene vs kekules structure

Answer 1

Benzene: 0.14nm bond length, -208 enthalpy of hydrogenation
Kekules: 0.153 and 0.134 bond length, -360 enthalpy of hydrogenation
Benzene is more stable than predicted structure
Due to delocalised ring of electrons

Question 2

Benzene structure

Answer 2

P orbitals overlap sideways to form ring of charge above and below ring
Delocalisation of p electrons makes more stable as fewer electron repulsion
Bond angles 120° so no strain in arrangement

Question 3

Nitration of benzene

Answer 3

Sulfuric acid and nitric acid at 50°C ( prevent further nitration)
H2SO4 + HNO3 <=> HSO4- + H2NO3+
H2NO3+ -> NO2+ + H2O
NO2 replaces H atom on benzene
Nucleophilic substitution
Can manufacture explosives (TNT)
Reduced to form amines

Question 4

Acylation of benzene

Answer 4

CH3COCl + AlCl3 -> CH3CO+ + AlCl4-
CH3CO+ acts as nucleophile replacing H atom
Catalyst regenerated H+ + AlCl4- -> AlCl3 + HCl
Anhydrous conditions to prevent hydrolysis