VJC 2024 Arenes Lesson Student Notes

1 VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT Mrs Mah Ai Ling / poh.ailing@vjc.edu.sg JC1 H2 CHEMISTRY ARENES (AROMATIC HYDROCARBON) Lecture 1 2 Pages 1 – 11 12 – 21 Complete by T3W10 T3W10 Tutorial questions 1 – 5 6 – 9 ______________________________________________________________________________ LECTURE OUTLINE 1 Introduction 1.1 Structure of Benzene 1.2 Nomenclature 2 Physical Properties of Arenes 3 Benzene 3.1 Preparation 3.2 Electrophilic Substitution Reactions 3.2.1 Halogenation 3.2.2 Nitration 3.2.3 Friedel-Crafts Alkylation 3.3 Addition of Hydrogen Reaction (Reduction) 4 Methylbenzene 4.1 Structure of Methylbenzene 4.2 Preparation 4.3 Reactions 4.3.1 Effect of Substituent Groups 4.3.2 Electrophilic Substitution Reactions (similar to benzene) 4.3.3 Addition of Hydrogen Reaction (Reduction) (similar to benzene) 4.3.4 Free Radical Substitution Reaction (side-chain reaction similar to alkanes) 4.3.5 Oxidation Reaction (side-chain reaction) 5 Summary REFERENCES 1 Modern Organic Chemistry by R.O.C. Norman and D.J.Waddington 2 Principles of Organic Chemistry by Peter R.S. Murray 3 A-Level Chemistry by E.N. Ramsden 4 Chemistry in Context by Hill and Holman

2 LEARNING OUTCOMES Candidates should be able to: (a) explain, in terms of delocalisation of π electrons, the difference between benzene and alkene: (i) reactivity towards electrophiles (ii) preference of benzene to undergo substitution rather than addition reaction (b) describe the chemistry of the benzene ring as exemplified by the following reactions of benzene and methylbenzene: (i) electrophilic substitution reactions with chlorine and with bromine (recognise the use of Lewis acid as catalysts) (ii) nitration with concentrated nitric acid (recognise concentrated sulfuric acid as a Br ønsted- Lowry acid catalyst) (iii) Friedel-Crafts alkylation with halogenoalkanes (recognise the use of Lewis acid as catalysts) (c) (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 (d) 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 (e) predict whether halogenation will occur in the side- chain or aromatic nucleus in arenes depending on reaction conditions (f) apply the knowledge of positions of substitution in the electrophilic substitution reactions of mono-substituted arenes

3 1 Introduction 1.1 Structure of Benzene • The molecular formula of benzene is C6H6. • The six carbon atoms of benzene are arranged in a hexagonal ring. Each carbon atom of the benzene molecule is sp 2 hybridised and uses two of the three sp 2 hybrid orbitals to