Chemistry- Arenes

Question 1

Why would we expect Benzene (C6H6) to be very reactive and why is it not the case?

Answer 1

Since the molecule has lots of double bonds it should be very reactive for addition reactions (electrophilic addition). Due to the system of delocalised electrons this means that Benzene is unusually stable.

Question 2

What was Kekule’s structure for Benzene?

Answer 2

(CH)=(CH)-(CH)=(CH)-(CH)=(CH) in a cyclic formation.

Question 3

Give the IPAC name for Kekule’s structure of Benzene

Answer 3

Cyclohexa-1,3,5-triene

Question 4

What are the porblems with Kekule’s structure of benzene?

Answer 4

1) Would expect a lot of electrophilic addition reactions! However Benzene does not react like this.
2) Bond length - Due to C-C and C=C bonds being different lengths we would expect Benzene to be an irregular hexagon. This is not the case as Benzene is regular and therefore there must be an average bond length suggesting a resonating bond (system of delocalised electrons). In Benzene all the bonds are of equal length.

Question 5

How is the system of delocalised electrons useful?

Answer 5

The resonance of the 4th bond of each carbon atom creates a system of delocalised electrons which is unusually stable.