6.1.1 Aromatic Compounds

State the formula of Benzene?

C6H6

which 2 models represent benzene?

• the kekule model

• the delocalised model

what does a benzene molecule consist of?

• a cyclic structure with 6 carbon atoms joined together in a ring

what type of compound is benzene classified as?

an aromatic compound/arene

what did kekule suggest benzene was made up of?

• that benzene was made up of a planar ring of carbon atoms with alternating double and single bonds between them

why is kekule’s model incorrect?

• if benzene consisted of alternating double and single bonds it would react like an alkene

• by electrophilic addition

• but benzene does not carry out electrophilic addition

• also doesn’t give positive bromine water test

• therefore benzene does not contain double bonds

• x ray diffraction tells us that single carbon bonds are longer than double carbon bonds

• however in benzene both have same length

• structure of benzene is more stable than kekules proposed model

state the name of the catalyst used to create an electrophile?

• a halogen carrier

what is the name of the reaction when benzene reacts with an electrophile?

electrophilic substitution

why is benzene unable to directly react with a molecule of bromine?

because the pi electrons are delocalised, the electron density between any two adjacent carbon atoms is not enough to induce a dipole in the bromine molecule

what catalyst is needed so that benzene can react with bromine?

a halogen carrier- FeBr₃ or AlBr₃

under what condition is bromination carried out under/

RTP

what type of reaction is bromination

• electrophilic substitution

what occurs during alkylation?

a methyl group is added to the benzene ring

in alkylation what are the reactants refluxed with?

refluxed with aluminium chloride

what does aluminium chloride act as?

a halogen carrier catalyst

what group does phenol have directly bonded to the benzene ring?

a hydroxyl group

why does phenol react more readily with electrophiles than benzene

• a lone pair of electrons in a p orbital on the oxygen atom is donated into the delocalised electron structure of the benzene ring

• this increased the electron density in the benzene ring

• therefore there is a greater attraction between the benzene ring and electrophiles

under what conditions does phenol react readily with bromine water

• RTP

what change happens to the bromine water in the bromination of phenol?

the bromine water decolourises from orange to colourless

why does bromination of phenol not require a halogen carrier catalyst?

due to the increased electron density of the benzene ring in phenol the phenol molecule can induce a dipole in a molecule of bromine

what are the reactants and conditions for the nitration of phenol?

• dilute nitric acid at RTP

why is phenol less soluble in water compared to other alcohols?

due to the non polar benzene ring

when dissolved in water why is phenol a weak acid?

because a proportion of phenol molecules reversibly dissociate