Aromatics

Question 1

Explain the bonding in and shape of a benzene molecule (6)

Answer 1

Bonding
* each C has 3 covalent bonds
* spare electrons (in a p orbital) overlap (to form pi cloud)
* delocalisation

Shape
* planar
* 6 carbon ring (hexagon)
* C-C bonds equal in length

Question 2

Reasons Kekule model was wrong (3)

Answer 2

• didn’t readily undergo electrophilic substitution
• all 6 C–C bonds similar in length (smaller than single and longer than double)
• ring more thermodynamically stable than expected (AH hydrogenation less exo than expected)

Question 3

Equation for Formation of electrophiles:

Answer 3

AlCl3 + Cl2 -> AlCl4– + Cl+
FeBr3 + Br2 -> FeBr4– + Br+