M6 Aromatic Compounds

Evidence to disprove Kekulés Model

Benzene does not react with bromine water at room temperature & pressure

The carbon-carbon bond lengths in benzene are all the same

The enthalpy of hydrogenation of benzene is less exothermic than expected

Orbital overlap in benzene

Kekulé model

Delocalised Model

Similarities between Kekulé & delocalised model

Both models show sideways overlap of p orbitals

Both models have a pi bond which lies above and below the plane of the carbon atoms

Differences between Kekulé & delocalised model

Delocalised - p orbitals overlap forming a delocalised pi system

Kekulé - there are 3 pi bonds.Each is localised over one carbon to carbon bond

Benzene

Delocalised electrons in a pi system

Lower electron density

Less able to polarise an electrophile (requires halogen carrier

Cyclohexene

Localised electrons in a pi bond between two carbon atoms

Higher electron density

More anle to polarise an electrophile

Nitration of benzene

Nitration of benzene (mechanism)

Reduction of nitrobenzene (+ conditions)

Halogenation of benzene

Halogenation of Benzene (mechanism)

Alkylation of benzene

Alkylation of benzene (mechanism)

Acylation of benzene

Acylation of benzene (mechanism)