haloalkanes

• Halogenoalkanes


  Insoluble in water as C-H bonds are non-polar, not compensated for enough by C-X bond polarity
• Halogenoalkanes


  Have a polar bond due to halogen having higher electronegativity than carbon (halogen is δ-, carbon is δ+)
• Halogenoalkanes


  • Have permanent dipole-dipole and van der Waals forces of attraction due to C-X bond polarity
• Halogenoalkanes


  Have higher boiling points with increase in carbon chain length and halogen further down group 7
• Haloalkanes


  Have greater mass than alkanes of the same chain length as mass of halogen > mass of H
• Reactivity of halogenoalkanes


  Most important factor is carbon-halogen bond enthalpy, which decreases down the group so reactivity increases down the group

  
• Nucleophile


  A negatively charged ion/δ− atom with a lone pair of electrons which can be donated to an electron deficient atom
• Nucleophiles


  • :OH-
  • :CN-
  • :NH3
• Nucleophilic substitution


  A reaction where a nucleophile donates a lone pair of electrons to δ+ C atom, δ− atom leaves molecule (replaced by nucleophiles)
• Reaction of bromoethane with NaOH (aq)


  Mechanism

  
• Reaction of bromoethane with KCN


  Mechanism

  
• Reaction of bromoethane with NH3

  Mechanism

  
• Reaction of bromoethane with NaOH in ethanol

  Mechanism

  
• CFCs


  Chlorine-fluoro-carbons - haloalkanes containing C, F and Cl only (no H)
• Although unreactive under normal conditions, CFCs catalyse the breakdown of ozone in the atmosphere via free radical substitution
• Replacements for CFCs


  • HCFCs (hydrogen, chlorine, fluorine, carbon)
  • HFCs (hydrogen, fluorine, carbon)
• Elimination reaction of haloalkanes

  Conditions/reactants: NaOH or KOH dissolved in ethanol (no water present), heated

  
• Elimination reaction of haloalkanes

  Forms an alkene, water and halogen ion