Halogenoalkanes

• Halogenoalkanes contain polar bonds as the halogens are more electronegative than carbon atoms
• Electron density is drawn towards the halogen forming ∂+ and ∂- regions
• Nucleophiles are species that contain a lone electron pair attracted to ∂+ regions of molecules
• Common nucleophiles include:

  • CN:
  • NH3
  • OH
• Nucleophilic substitution is the reaction mechanism where nucleophiles attack halogenoalkanes
• It can produce alcohols or amines from halogenoalkanes - Nucleophilic Sub
• In nucleophilic substitution reactions, the greater the Mr of the halogen in the polar bond, the lower the bond enthalpy, making it easier to break
• Nucleophilic substitution reactions can only occur for 1o (primary) and 2o (secondary) halogenoalkanes
• Elimination reactions occur when a halogenoalkane is heated to high temperatures under alcoholic conditions
• The nucleophile acts as a base and accepts a proton, removing a hydrogen atom from the molecule - Elimination
• This results in the elimination of the halide, producing a carbon-carbon double bond (alkene) - Nucleophile is a base
• Elimination reactions can only occur from 2o and 3o (tertiary) halogenoalkanes
• Ozone in the atmosphere absorbs UV radiation
• CFCs absorb UV radiation, breaking down the carbon-halogen bonds to form free radicals that catalyse ozone depletion
• CFC-free solvents are being produced to prevent ozone depletion and global warming