Aromatic Compounds

Question 1

Formula of benzene

Answer 1

C6H6

Question 2

What was Kekule’s model of benzene?

Answer 2

Benzene was made up of a planar (flat) ring of carbon atoms with alternating single and double bonds between them.

He later adapted the model to say that the benzene molecule was constantly flipping between two forms (isomers) by switching over the double and single bonds.

Question 3

Evidence for the delocalised model of benzene

Answer 3

Bond length – X-ray diffraction patterns show the C-C bond lengths in benzene are all the same, being in between the length of carbon single and double bonds

Hydrogenation – The enthalpy change of hydrogenation for benzene is less exothermic than that of theoretical cyclohexa-1,3,5-triene, showing that benzene is more stable than the Kekule model

Resistance to reaction – benzene does not decoulorise bromine water like normal alkenes do, and it does not undergo electrophilic substitution addition reactions