ASRJC 2024 H2 Chem Arenes

2024 ASRJC JC1 H2 Arenes 2024/AndersonSerangoonJC/Chemistry 1 Anderson Serangoon Junior College JC1 H2 Chemistry ARENES CONTENT 1 Introduction 2 Benzene 3 Reactions of Benzene 4 Reactivity of Mono-substituted Aromatic Rings 5 Methylbenzene 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 Bronsted-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. References 1. A-Level Chemistry by E.N. Ramsden 2. Understanding Chemistry for Advanced Level by Ted Lister and Janet Renshaw 3. Chemistry in Context by Graham Hill and John Holman

2024 ASRJC JC1 H2 Arenes 2024/AndersonSerangoonJC/Chemistry 2 1 Introduction Arenes, also known as aromatic hydrocarbons, are hydrocarbons which are derivatives of benzene, C6H6. The word ‘aromatic’ was initially associated with pleasant smell, but it was later accepted as structures that are stabilised by a ring of delocalised  electrons. The simplest arene is benzene itself. Benzene Naphthalene 2 Benzene 2.1 Properties • A colourless liquid at room temperature with a characteristic smell. • C:H ratio is 1:1. • Burns with a smoky and luminous flame due to its high carbon content. • Non-polar in nature hence is immiscible with water but mix with other hydrocarbons and ot