Arenes are aromatic hydrocarbons. The term “aromatic” originally referred to their pleasant smells (e.g., from cinnamon bark, wintergreen leaves, vanilla beans and anise seeds), but now implies a particular sort of delocalized bonding. Aromatic hydrocarbons (or sometimes called arenes or aryl hydrocarbon) are hydrocarbons with sigma bonds and delocalized π electrons between carbon atoms forming rings.
Course Contents
- Arenes (exemplified by benzene and methylbenzene)
- (i) influence of delocalised π electrons on structure and properties
- (ii) electrophilic substitution reactions
- (iii) oxidation of side-chain
Learning Outcomes
Candidates should be able to:
- (a) explain, in terms of delocalisation of π electrons, the difference between benzene and alkene:
- (b) reactivity towards electrophiles
- (ii) preference of benzene to undergo substitution rather than addition reaction
- (i) describe the chemistry of the benzene ring as exemplified by the following reactions of benzene and methylbenzene:
- (c) electrophilic substitution reactions with chlorine and with bromine (recognise the use of Lewis acid as catalysts; see also Section 4)
- (ii) nitration with concentrated nitric acid (recognise concentrated sulfuric acid as a Brønsted-Lowry acid catalyst; see also Section 4)
- (iii) Friedel-Crafts alkylation with halogenoalkanes (recognise the use of Lewis acid as catalysts; see also Section 4)
- (d)
- (i) describe the mechanism of electrophilic substitution in arenes, using the mono-bromination of benzene as an example
- (ii) describe the effect of the delocalisation of electrons in arenes in such reactions
- (e) describe the chemistry of the alkyl side-chain of benzene ring as exemplified by the following reactions of methylbenzene:
- (i) free-radical substitution by chlorine and by bromine
- (ii) complete oxidation to give benzoic acid
- (f) predict whether halogenation will occur in the side-chain or aromatic nucleus in arenes depending on reaction conditions
- (g) apply the knowledge of positions of substitution in the electrophilic substitution reactions of monosubstituted arenes