Free radical substitution

• State a use for chloroalkanes and chlorofluoroalkanes

  chloroalkanes and chlorofluoroalkanes can be used as solvents
• What gaseous product is always formed when a halogen reacts with an alkane in a free radical substitution reaction

  a hydrogen halide is always formed i.e. methane + chlorine -> chloromethane + hydrogen chloride
• State what occurs during propagation

  1. a halogen radical reacts with an alkane molecule. A C-H bond in the alkane breaks by homolytic fission. An alkyl radical and hydrogen halide form.
  2. The alkyl radical reacts with a halogen molecule, haloalkane is formed together with a halogen radical which reacts with another molecule of alkane
  3. Repeat first 2 steps
• what occurs during initiation?

  UV light breaks covalent bond in halogen molecule by homolytic fission (both atoms gaining 1 electron each from the shared bonding pair of electrons). Two very reactive radicals are formed.
• State the three steps in free radical substitution

  1.initiation 2.propagation 3.termination
• what does substitution mean

  replacement of one group with another
• what does the . represent on a free radical

  an unpaired electron
• What is a radical

  a species with an unpaired electron
• What are the limitations of free radical substitution?

  • further substitution
  • substitution at different positions in a carbon chain
• What occurs during termination?

  Two radicals collide forming a molecule
• Equation for initiation: Cl2 -> (UV light)

  .Cl +.Cl
• Equation for step 1 of propagation: .Cl + CH4 ->

  HCl + .CH3 (radical methyl - carbon loses 1 electron)
• Equation for step 2 of propagation: .CH3 + Cl2 ->

  CH3Cl + .Cl
• An example equation for termination: .Cl + .Cl -> Cl2