Aromatic Compounds
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What can bonding in benzene be described in terms of?
sp2 hybridisation, sigma and pi bonds, and electron delocalisation
What is the simplest aromatic compound?
benzene
What is benzenes unexpected stability attributed to?
the presence of delocalised electrons
In benzene, what does the overlap of p-orbitals above and below the planar ring make?
circular electron clouds
Describe how the delocalised electrons form in benzene?
Each carbon atom is sp2 hybridised - the three orbitals on each carbon atoms form a planar ring. The remaining p orbitals overlap in both directions to give a ring of delocalised electrons above and below the plane of the molecule.
Explain why Kekules structures can be discounted.
X-ray analysis confirms the bonds between the carbon atoms are all the same length, and are intermediate in length between a single and a double bond.
What does the lack of double bonds in benzene explain?
the resistance of benzene to undergo addition reactions
What are compounds which show electron delocalisation known as?
aromatic compounds
What type of reactions can aromatic compounds undergo?
electrophilic substitutions
In benzene what are the 6 delocalised electrons readily available to ?
attacking electrophiles
What 3 electrophilic substitutions can benzene undergo?
Halogenation Nitration Sulphonation
Give examples of catalysts used in halogenation?
iron (III) bromide Aluminium chloride
Describe how the catalyst works in halogenation?
it polarises the halogen by accepting a pair of electrons from one of the atoms creating an electrophilic centre
Describe nitration.
A mixture of conc sulphuric acid and conc nitric acid to generate a nitronium ion NO2+. This is the attacking electrophile
What is the attacking electrophile in sulphonation?
HSO3+