12.2 Chemical reaction of alkanes

• • Combustion occurs with diatomic oxygen
  • Complete combustion produces carbon dioxide and water
  • When oxygen is scares incomplete combustion form carbon monoxide, can also form carbon (soot)
• Haloalkane reaction:

  Alkanes can react with halogens if high energy ultraviolet is present

  The reaction takes place in three step:

  • initiation
  • propagation
  • termination

  This reaction mechanism is an example of radical substitution
• Initiation:

  Reaction is started when the covalent bond in the bromine molecule is broken by homolytic fission
• Propagation:

  Reaction propagates through two steps in a chain reaction

  • propagation step 1: CH4 + Br• — •CH3 + HBr
  • propagation step 2: •CH3 + Br2 — CH3Br + Br•

  This process continues for a long time because the radicals are highly reactive
• Termination:

  Radicals collide to form molecules that have fully paired electrons