ChemistryCode 9701
Halogenoalkanes
What this topic asks you to be able to do
- state the reagents and conditions used to make halogenoalkanes: (a) free-radical substitution of alkanes with Cl2 or Br2 under ultraviolet light, for example with ethane (b) electrophilic addition to an alkene using a halogen, X2, or hydrogen halide, HX(g), at room temperature (c) substitution of an alcohol, e.g. with HX(g); with KCl and concentrated H2SO4 or concentrated H3PO4; with PCl3 and heat; with PCl5; or with SOCl2
- classify halogenoalkanes as primary, secondary or tertiary
- describe these nucleophilic substitution reactions: (a) producing an alcohol when heated with NaOH(aq) (b) forming a nitrile when KCN in ethanol is heated (c) forming an amine when NH3 in ethanol is heated under pressure (d) the reaction with aqueous silver nitrate dissolved in ethanol, used to identify which halogen is present, using bromoethane as an example
- describe the elimination reaction in which NaOH dissolved in ethanol, with heating, forms an alkene, using bromoethane as an example
- describe and explain the mechanisms SN1 and SN2 by which halogenoalkanes undergo nucleophilic substitution, including the inductive effects arising from alkyl groups
- state that primary halogenoalkanes usually follow the SN2 mechanism; tertiary ones follow the SN1 mechanism; and secondary ones use a mix of both, depending on their structure
- describe and explain why halogenoalkanes differ in reactivity, focusing on how the strengths of their C–X bonds compare, as shown by their reactions with aqueous silver nitrates