14 Arenes

Question 1

Arenes

Answer 1

Hydrocarbons that possess at least one benzene ring

Question 2

Resonance structure in a benzene ring

Answer 2

Continuous overlap of unhybridised p-orbitals resulting in the delocalisation of π electrons above and below the ring

Question 3

Stability of benzene

Answer 3

Delocalisation of π electrons results in high stability of benzene.
Stronger electrophile required for electrophilic attack

Question 4

Physical properties of benzene

Answer 4

1. Colourless
2. Insoluble in water, soluble in non-polar solvents
3. Less dense than water

Question 5

Nitration of benzene

Answer 5

conc. HNO3, conc. H2SO4
maintained at 55°C
(temp changes with presence of activating/deactivating groups)

Question 6

Halogenation of benzene

Answer 6

X2, Fe/anhydrous FeX3/anhydrous AlX3
(Only for Br and Cl)

Question 7

Friedal-Crafts alkylation

Answer 7

RCl, anhydrous AlCl3/FeCl3

Question 8

Friedal-Crafts acylation

Answer 8

RCOCl, anhydrous AlCl3

Question 9

Physical properties of methylbenzene

Answer 9

1. Colourless liquid
2. Insoluble in water, soluble in non-polar solvents
3. Higher boiling point than benzene
4. Lower melting point than benzene

Question 10

Oxidation of alkylbenzenes

Answer 10

Acidified KMnO4, heat under reflux
Benzoic acid, H2O, CO2 (except methylbenzene) formed