A2: Aromatics

Question 1

Define arene

Answer 1

An aromatic hydrocarbon containing a benzene ring

Question 2

What is benzene?

Answer 2

The simplest aromatic hydrocarbon, found in crude oil, petrol, cigarette smoke. It is a colourless, sweet, flammable liquid

Question 3

Describe the delocalised model

Answer 3

Has a sideways overlap of p-orbitals above and below the plane, causing a π-system, with 3 electrons per bond

Question 4

Evidence to disprove Kekule’s model - explained

Answer 4

1) From x-ray diffraction the bonds were measured to be in between the length of a single and double bond
2) Kekule’s model predicts the enthalpy of hydrogenation to be -360kJmol-1, but is actually less negative, so more stable
3) It doesn’t decolourise bromine water so doesn’t undergo addition under normal conditions as it more stable

Question 5

Summary - evidence disproving Kekule’s model

Answer 5

Bond length, hydrogenation, no addition

Question 6

Nitration of benzene

Answer 6

Reacts with nitric acid to form nitrobenzene and water (sulfuric acid catalyst, 50 degrees c)

Question 7

Common halogen carriers

Answer 7

AlCl3, FeCl3, AlBr3 and FeBr3