27.2 Arenes: Physical properties, naming and reactivity

Question 1

What state and colour is benzene at room temperature

Answer 1

. Colourless liquid at room temperature

Question 2

Why does benzene have a much higher melting point than hexane

Answer 2

. It has flat hexagonal molecules which pack together very well in the solid state

They are therefore harder to separate and this must happen for the solid to melt

Question 3

Are arenes soluble in water

Answer 3

. No because they are non-polar so don’t mix with water but do with other hydrocarbons and non polar solvents

Question 4

How do you name aromatic compounds

With one substituent

Answer 4

Arenes are usually derivatives of benzene, so benzene forms root of the name

With one substituent eg CH3 in replace of H, C6H5CH3 is methylbenzene
Or with substituent Cl in replace of H it is chlorobenzene

Question 5

How do you name aromatic compounds

With two substituents

Answer 5

Here, the ring is numbered.

So if two chlorines are added:
So 1,2-dichlorobenzene
Or 1,4-dichlorobenzene

Question 6

Are aromatic compounds reactive

Answer 6

. The ring is an area of high electron density because of the delocalised bonding, and is therefore attacked by electrophiles

. The aromatic ring is very stable and needs energy to be put in to break the ring before the system can be destroyed.
This is called delocalisation energy, so the ring almost always remains intact in the reactions of arenes

So this means aromatic systems can undergo electrophilic substitution reactions