6.1 aromatic compounds

Question 1

what does the kekule model suggest:

Answer 1

that benzene has alternating structure of double and single bonds

Question 2

what does the delocalised model suggest:

Answer 2

that benzene has a delocalised ring of electrons

Question 3

evidence that supports the delocalised model (3)

Answer 3

1. resistance to reactions
   it doesn’t undergo electrophilic additions/decolourise bromine water
2. intermediate bond length
   if it had alternating the bonds would be 0.134nm and 0.153nm. bonds in benzene have the same length of 0.139nm
3. enthalpy change of hydration
   cyclohexane = -120kJmol so kekule model shows it would be -360kJmol but it is -208kJmol

Question 4

aromatic compound

Answer 4

contains a benzene ring

Question 5

when is the prefix ‘phenyl’ used

Answer 5

when a benzene is substituted with a carbon chain longer than 6 carbons or the carbon chain has another functional group.

Question 6

why is benzene more likely to undergo electrophilic sub. than addition?

Answer 6

1. the ring structure remains intact as its very stable so large amounts of energy is required to break the ring system
2. the high electron density of the pi-system means electrophiles are readily attracted to it, more than the electron density of the pi-bond in alkenes