ASRJC 2025 H2 Chem Halogen Derivatives Notes

2025 JC2 H2 Halogen Derivatives 2025/ASRJC/Chemistry 1 Anderson Serangoon Junior College JC2 H2 Chemistry HALOGEN DERIVATIVES Learning Outcomes Candidates should be able to: (a) recall the chemistry of halogenoalkanes as exemplified by (i) the following nucleophilic substitution reactions of bromoethane: hydrolysis; formation of nitriles; formation of primary amines by reaction with ammonia (ii) the elimination of hydrogen bromide from 2−bromopropane (b) describe and explain the mechanisms of nucleophilic substitutions in halogenoalkanes (i) SN1, in terms of stability of the carbocation intermediates (ii) SN2, in terms of steric hindrance of the halogenoalkanes (c) explain the stereochemical outcome in nucleophilic substitution involving optically active substrates: (i) inversion of configuration in SN2 mechanism (ii) racemisation in SN1 mechanism (d) interpret the different reactivities of halogenoalkanes, with particular reference to hydrolysis and to the relative strengths of the C−Hal bonds (e) explain the unreactivity of chlorobenzene compared to halogenoalkanes towards nucleophilic substitution, in terms of the delocalisation of the lone pair of electrons on the halogen and steric hindrance (f) suggest characteristic reactions to differentiate between: (i) different halogenoalkanes (ii) halogenoalkanes and halogenoarenes e.g. hydrolysis, followed by testing of the halide ions (g) explain the uses of fluoroalkanes and fluorohalogenoalkanes in terms of their relative chemical inertness (h) recognise the concern about the effect of chlorofluoroalkanes (CFCs) on the ozone layer [the mechanistic details of how CFCs deplete the ozone layer are not required] References 1. Chemistry for Advanced Level by P. Cann & P. Hughes 2. Organic Chemistry (6th edition) by McMurry 3. A−Level Chemistry by E.N. Ramsden 4. Understanding Chemistry for Advanced Level by Ted Lister and Janet Renshaw 5. Chemistry in Context by Graham Hill and John Holman

2025 JC2 H2 Halogen Derivatives 2025/ASRJC/Chemistry 2 1. INTRODUCTION • Halogen derivatives are a homologous serie s of organic compounds containing one or more halogen atoms. • General formula: CnH2n+1X (where X = F, Cl, Br or I). • They are important intermediates in organic synthesis. • 2 types: halogenoalkanes and halogenoarenes Haloge