benzene

Kekule model

Proposed that benzene was made up of a planar ring of carbon atoms with alternating double and single carbon bonds with each carbon atom being bonded to a singular H atom. He stated that Benzene was constantly flipping between two isomers by switching the double bonds over

Why was the kekule model inaccurate

X-ray diffractions studies have shown that all the carbon-carbon bonds have the same length even though single and double carbon bonds have different lengths. If benzene contained double bonds it would be able to de colourise bromine water but it doesn’t as benzene doesn’t u Sergio electrophilic addition reactions. Benzene should also have an ent halos change of hydrogenation 3 times that of cyclohexane (-360Kjmol) when in actuality it has a lower one (-208Kjmol)

Delocalised model

States that in benzene all the P-orbitals of the six carbons overlap to form a delocalised pie ring. This pie ring system is made up of two ring-shaped clouds one above and one below the plane. All the bonds have the same length.

Phenol aromatic compounds

When benzene is added to an alkyl chain with a functional group or a carbon chain over 7 carbon atoms long the prefix phenol is used to name the compound

Nitration of benzene reagents

Recquires a H2SO4 catalyst which reacts with HNO3 to form NO2+ and HSO4- and H20

Halogenation of benzene reagents

Needs a halogen carrier to occur such as AlCl3, AlBr3, FeBr3 or FeCl3

Alkylation of benzene

The substitution of a hydrogen atom with an alkyl group in a benzene ring to increase the length of the carbon chain. Needs AlCl3 as a catalyst

Acylation of benzene

When benzene reacts with an acyl chloride in the presence of and AlCl3 catalyst to form an aromatic ketone

Alkene Vs Benzene reactivity

Alkene is more reactive than benzene as it is able to decolourise bromine water while benzene can’t as the pie bond on alkene contains localised electrons above and below the plane of the two carbon atoms in the double bond creating an area of high electron density capable of inducing a dipole in the Br2 molecule whereas in benzene the pie ring contains delocalised electrons so has a lower electron density

Neutralisation reaction of phenol

Phenol reacts with NaOH to form the salt sodium phenoxide and water

Bromination of phenol

Reacts with an an aqueous solution of bromine to form a white precipitate of 2,4,6-tribromophenol. No halogen carrier is required

Nitration of phenol

Phenol reacts with a dilute nitric acid at room temperature to make of mixture of 2-nitrophenol and 4-nitrophenol

Why is phenol a weak acid

Because in water phenol partially dissociates to form a phenoxide ion and a proton

Phenol Vs benzene reactivity

Phenol is more reactive than benzene because a lone pair in the P-orbital of the oxygen atom in the OH group is donated into the pie ring system increasing its electron density making phenol more susceptible to attack by an electrophili