Haloalkanes

• Halo alkanes


  Alkanes with one or more halogen atoms attached
• Naming halo alkanes


  1. Find the longest carbon chain

  2. Prefix the names and positions of the halogens

  3. Halogens must be in alphabetical order

  4. Use prefixes like tri, di, tetra for multiple halogens
• Bond polarity


  Halogens are electronegative and pull electrons towards themselves, creating a polar bond
• Nucleophile


  An electron pair donor that attacks the delta positive carbon of the halo alkane
• Nucleophilic substitution reaction of halo alkanes with hydroxide

  1. Warm aqueous sodium hydroxide

  2. Nucleophile attacks delta positive carbon

  3. Halogen is kicked off

  4. Produces an alcohol
• Reaction of halo alkanes with water

  1. Heat the reaction

  2. Water is a weaker nucleophile than hydroxide

  3. Produces an alcohol and hydrogen halide
• Halo alkane reactivity


  • Increases down the halogen group as the carbon-halogen bond strength decreases
  • Iodine alkanes are the most reactive and hydrolysed fastest
• CFCs (chlorofluorocarbons) break down ozone in the atmosphere
• UV radiation breaks the carbon-chlorine bonds in CFCs, producing radical species</b>
• CFCs


  Chlorofluorocarbons that break down ozone (O3) in the atmosphere
• CFCs have all hydrogens replaced by chlorine and fluorine, making them stable molecules</b>
• UV radiation


  Breaks down CFC-C-Cl bonds, forming radicals
• Ozone destruction by CFCs

  1. Initiation: UV breaks down CFC to form Cl radical

  2. Propagation: Cl radical reacts with O3 to form ClO radical and O2

  3. Propagation: ClO radical reacts with more O3 to reform Cl radical and produce O2

  4. Termination: Two Cl radicals collide to form Cl2
• CFCs were previously used as refrigerants and propellants, but are now banned due to ozone damage
• Ozone layer absorbs harmful UV radiation from the sun, protecting living organisms
• Montreal Protocol bans use of CFCs in most products by 2000


  1989
• HFCs


  Hydrofluorocarbons used as temporary CFC alternatives, but are potent greenhouse gases
• Hydrocarbons


  Used as refrigerants, but are also greenhouse gases
• Ammonia


  Used as a relatively stable and less damaging refrigerant
• Ozone layer is slowly recovering due to reduced CFC use
• Reaction with hydroxide ions

  1. Warm aqueous sodium hydroxide as source of OH- ions
  2. Carried out under reflux
  3. A nucleophile will attack the slightly positive carbon and will replace the halogen
• CFCs break down to form chlorine radicals

  
• General equation for other radicals

  -