Arenes

Question 1

What is benzene and how can it be represented?

Answer 1

Benzene is the simplest arene, with the formula: C6H6.
Represented by Kekulé model: benzene is a 6 membered ring with alternating single and double bonds & the bonds are different lengths.
Also, be represented by the delocalised model.

Question 2

Why does benzene have a delocalised structure?

Answer 2

1) X-Ray diffraction has shown that all the bonds are the same length.
2) Delta H hydrogenation is less exothermic than expected compared to the Kekulé’s model. So it’s more thermodynamically stable.
3) Shows resistance to react with bromine, it will only do so in the presence of a halogen carrier.

Question 3

1) What are the conditions necessary for the nitration of benzene?
2) What are the conditions necessary for the halogenation of benzene?

Answer 3

1) Concentrated HNO3 in the presence of concentrated H2SO4. Mechanism: Electrophilic substitution. Electrophilic: NO2+.

Question 4

What’s the difference in the halogenation reaction in benzene and phenol?

Answer 4

1) Electrophilic substitution reactions occur more readily with phenol than with benzene. This is due to the lone electron pair on the O (of the OH group), which is delocalised into the ring, which increases the electron density inside the ring.
So, it’s more electron rich; can depolarise the electrophile without the use of on halogen carrier.

2) Benzene has 6 p electrons delocalised into the ring above and below the plane of carbons atoms = benzene is stable.
So, it’s unwilling to undergo addition reactions as it would destroy the stable ring.

Question 5

What type of mechanism occurs with the halogenation of cyclohexene - alkene?

Answer 5

Electrophilic addition. The C double bond C area is an area of high electron density. So, it’s strongly attracted to the electrophile.

Question 6

What is phenol?

Answer 6

Phenol has the formula: C6H5OH. It’s a weak acid; weaker than carboxylic acids.
However, it can react with Na metal and NaOH.

Question 7

What are the products when phenol reacts with:

1) Na metal
2) NaOH

Answer 7

1) Sodium phenoxide: O-Na+ & hydrogen

3) Sodium phenoxide & water.

Question 8

What are Arenes?

Answer 8

Arenes are compounds which contain unsaturated rings with delocalised electrons within the ring.