1. Aromatic Compounds

Describe the structure of benzene - 2

• planar

• cyclic

• (six carbon atoms joined together in a flat ring)

What is an aromatic compound

Aromatic compounds all contain a benzene ring.

draw the formation of a delocalised ring of electrons in benzene.

in textbook page 446

How to use hydrogenation to validate that benzene is more stable than an alkene?

Compare the enthalpy change of hydrogenation for benzene with the enthalpy change of hydrogenation of cyclohexene.

What is the enthalpy change of hydrogenation for a single H atom on cyclohexene

-120 kj mol^-1 

What is the enthalpy change of hydrogenation for a benzene ring compared to cyclohexene

• -208 kj mol^-1 and not -360

• 152 less exothermic than expected.

What is the reasoning behind why the enthalpy change of hydrogenation is lower in benzene

In a delocalised ring, the electron density is shared over more atoms, which means the energy of the molecule is lowered and it becomes more stable.

How does benzene being less exothermic than cyclohexene prove that it is more stable

It is less exothermic which means more energy must have been put in to break the bonds in benzene than in cyclohexene making it more stable.