Aromatic Chemistry

Question 1

What is the molecular formula for benzene?

Answer 1

C6H6

Question 2

What is the structure of benzene?

Answer 2

Planar cyclic.

Question 3

How does the ring of delocalized electrons form in benzene?

Answer 3

The two lone pair of electrons on the carbon are in a p-orbital. The p-orbitals stick out above and below the plane of the ring. They then combine to form a ring of delocalised electrons.

Question 4

Use numerical data to explain why benzene is more stable than expected.

Answer 4

The bond enthalpy of the theoretical compound is -360 kJ mol -1 and the bond enthalpy of the bonds in benzene is -208 kJ mol-1. The fact that the actual bond enthalpy is 152 kJ mol -1 less than the theoretical compound means that benzene is much more stable than theorised. This is because the reaction is less exothermic than expected and more energy was put in to break bonds.

Question 5

What is the functional group of an aromatic compound?

Question 6

Why do benzene rings attract electrophiles?

Question 7

What is the name of the mechanism where a benzene ring reacts with an electrophile?

Answer 7

electrophilic substitution.

Question 8

Name and draw the mechanism for when a benzene ring reacts with a nitronium ion.

Question 9

What are the conditions needed for nitration?

Answer 9

1. concentrated sulfuric acid and nitric acid.
2. temperatures below 55 degrees for monosubstitution.

Question 10

Write down the equation for the reaction of sulfuric acid and nitric acid to form a nitronium ion.

Answer 10

NO2 +

Question 11

What are the uses for nitration reactions?

Answer 11

1. Nitro compounds can be reduced to form amines. These can then be used to make dyes and pharmaceuticals.

Question 12

What is the acylation of benzenes?

Answer 12

Adding an acyl group to a benzene ring.

Question 13

What is an acyl group?

Question 14

Why is the acylation of benzene rings needed?

Answer 14

Many pharmaceuticals and dyes need benzene rings but since benzene is so stable is fairly unreactive. Adding an acyl group to the benzene rings allows them to react with other compounds.

Question 15

What are the conditions needed for acylation?

Answer 15

1. Heated under reflux
2. AlCl3

Question 16

What is the role of AlCL3 in the acylation of benzene rings?

Answer 16

It accepts a lone pair of electrons from the acyl chloride so that the acyl chloride becomes a much stronger electrophile.

Question 17

Why does the electrophile need to be very positive?

Answer 17

So that it is strong enough to attack the benzene ring.

Question 18

Write the equation for the formation of the carbocation from the reaction of an acyl chloride and AlCl3.

Question 19

Name and draw the mechanism for when ethanoyl chloride reacts with benzene to produce phenyl ethanoate.