organics 2

Question 1

describe the difference between the delocalised model of benzene and kekules model

Answer 1

Kekules model -
3 alternating double carbon bonds
expected to easily undergo addition reactions
carbon bonds different lengths

Delocalised model -
carbon bonds all the same length
each C atoms forms a 3 sigma bond and the spare P orbital overlaps sideways to create a delocalised ring system which forms 2 clouds of electron density above and below the ring

Question 2

what is the evidence for the delocalised model

Answer 2

enthalpy is hydrogenation is less exothermic than the C–C enthalpy of hydrogenation

carbon bonds are all the same lenght

Question 3

explain why benzene does not react readily with bromine compared with alkenes

Answer 3

benzene has a delocalise Pi system which is unable to induce a dipole into the non-polar Br2
this means it cannot act as an electrophile

alkenes have localised electron density in the Pi bond which can induce a dipole