Aromatic Compounds

Question 1

Formula for number of pi electrons?

Answer 1

4n + 2 pi electrons (Huckel’s rule)

Question 2

What does ortho, meta, para mean?

Answer 2

Ortho = side by side (1,2-dimethylbenzene)
Meta = one apart (1,3-dimethylbenzene)
Para = opposite sides (1,4-dimethylbenzene)

Question 3

Two steps of electrophilic aromatic substitution?

Answer 3

1) Electrophilic attack

2) Loss of hydrogen

Question 4

Why doesn’t benzene undergo addition reactions?

Answer 4

Because that would disturb the stabilizing aromaticity of the compound

Question 5

Explain sulfonation of benzene

Answer 5

Benzene + hot SO3/H2SO4 to produce sulfonic acid (Benzene + SO3H)

Question 6

Explain nitration of benzene

Answer 6

Benzene + HNO3 + H2SO4 –> benzene + NO2. Mixture of acids creates NO2+ ion, strong electrophile. Nitronium reacts with the ring.

Question 7

Explain benzene acylation (Friedel-Crafts reaction)

Answer 7

Lewis acid turns acyl group into a carbocation which attacks ring to add acyl group.

Question 8

Where do activators direct new substituents?

Answer 8

To ortho or para positions

Question 9

Where do deactivators direct new substituents?

Answer 9

To meta positions, with the exception of halogens.

Question 10

Explain catalytic reduction of benzene

Answer 10

Benzene + H2 + Rh/C + high heat/pressure –> reduction to cyclohexane

Question 11

Explain halogenation of benzene?

Answer 11

Br2 or Cl2 in presence of corresponding Lewis acid (FeBr3/AlBr3/FeCl3/AlCl3) and heat produce good yield of monosubstituted product.