- Created by: Em
- Created on: 04-10-10 11:43
Arenes are aromatic hydrocarbons containing on or more benzene rings.
A benzene is a ring of 6 carbons, each of which are bonded to one hydrogen atom.
Kekules model failed to explain benzene's low chemical reactivity;
- If C=C double bonds were presemt then benzene would react in a similar way to alkenes
- each C=C double bond would be expected to react with bromine water, decolourising it.
Benzene doesn't take part in other electrophilic addition reactions expected from the C=C bond in alkenes.
Kekule refinde his structure of benzene, he suggested benzene had two forms, differing only by the positions of the double bonds. He suggested that these two forms of benzene were in such a rapid equilibrium that an approaching bromine molecule couldn't be attracted to a double bond before the structure change.
However the C=C, and C-C bonds have different lengths, wheras Kekule said they were symmetrical.
The structure of benzene has much less energy than the propose kekule structure, the real structure of benzene is 152 KJ mol-1 more stable than the kekule structure - this energy is known as the delocalisation energy of benzene.
The evidence suggests that the real structure of benzene is more stable than a structure containing C=C bonds. This helps to explain why benzne is less reactive than alkenes.
Delocalise electrons are shared between more than two atoms.
The weaknesses in Kekules structure led to the development of the delocalised model…