synthesis of halogenoalkanes

• what mechanism is chlorination?

  free radical substitution
• what is a free radical?

  species with single unpaired electron
• what is a substitution reaction?

  atom is replaced with different atom
• why can halogens act as radicals?

  halogen atom has 7 outer electrons

  3 pairs of electrons

  1 lone unpaired electron to act as radical
• how is a radical represented?

  X.
• what is the process of free radical substitution?

  1. initiation
  2. propagation
  3. termination
• what do initiation require?

  UV light to provide energy to break X-X
• what type of reaction is initiation?

  homolytic fission
• what is an example of initiation?

  UV

  Cl2 --> 2Cl.
• what is an example of propagation?

  Cl. + CH4 --> HCl + .CH3

  .CH3 + Cl2 --> CH3Cl + Cl.
• what is the process of termination?

  any 2 radicals coming together to form stable molecules
• what is an example of termination?

  Cl. + .CH3 --> CH3Cl
• what is the overall equation for this given reaction?

  CH4 + Cl2 --> HCl + CH3Cl
• why can free radical substitutions make multiple products?

  termination reactions

  further substitution reactions
• what is a further substitution reaction?

  halogenoalkane product attacked by free radical
• what is further substitution caused by?

  excess Cl
• how can further substitution be prevented?

  excess alkane
• what is an example of further substitution?

  CH4 + Cl2 --> CH3Cl + HCl

  CH3 + Cl2 --> CH2Cl2 + HCl

  CH2 + Cl2 --> CHCl3 + HCl

  CH + Cl2 --> CCl4 + HCl