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6 Cards in this Set

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Benzene

Molecular Formula = C6H6


Molecules containing benzene rings are called aromatic compounds


Bonding in Benzene

Benzene is a planar hexagon w/ a π cloud of electrons above and below the ring.


The electrons are fused together p-orbitals.


Spreading the electrons stabilises the molecule.


The bonds aren't in fixed positions (resonance theory)

Kekule vs Benzene structure

1) Expected ∆H of hydrogenation in kekule is -360 kJmol-1 (3 x ∆H of cyclohexene).


Actual ∆H of hydrogenation is -208kJmol-1.


"Enthaply of hydrogenation is less exothermic than the theoretical cyclohexatriene."


2) benzene doesn't react with bromine water at room temp. Cyclohexene does


3) X-ray crystallography shows the bond length to be all the same at 0.139nm, between the length of a


C-C and a C=C bond

Electrophilic Substitution

The first stage of the process is slow and is known as the rate determining step (RDS) of the reaction the second stage is fast as the unstable intermediate breaks down.

Nitration of benzene

Benzene is refluxed in a water bath at 60°C with a mixture of concentrated sulphuric acid (catalyst) and concentrated nitric acid

Halogenation of Benzene

Requires a halogen carrier catalyst (FeBr3 or AlCl3)