Chapter 27 - Aromatic chemistry

Question 1

Describe how addition reactions support the delocalised structure of benzene

Answer 1

If benzene instead contained 3 C=C, it would readily undergo addition reactions

But it doesn’t

Question 2

Describe how bond lengths support the delocalised structure of benzene

Answer 2

Measurements from x-ray diffraction show that carbon carbon bonds in benzene are all the same length

If the original structure was right there would be 3 long bonds (C-C) and 3 short (C=C)

Question 3

Describe how enthalpy of hydrogenation values support the delocalised structure of benzene

Answer 3

Benzene is 152 kJ per mol stable than the original structure would be

This is because of the ‘electron cloud’ and the delocalisation stability

Question 4

Describe the melting and boiling point of benzene

Answer 4

• Boiling point is similar to hexane
• Melting point is much higher than hexane because the flat molecules pack together very well in solid state

Question 5

Describe the solubility of arenes in water

Answer 5

Non-polar so are not soluble

Question 6

Describe the combustion of arenes

Answer 6

• Burn in air with smoky flame
• Higher carbon:hydrogen ratio than alkanes
• Unburnt hydrocarbons are seen as smoke

Question 7

What are the uses of nitration?

Answer 7

• Production of explosives
• Producing aromatic amines which are then used to make industrial dyes