substitution reactions

• Why are alkanes very unreactive?

  Their CC and CH bonds are very strong and therefore require lots of activation energy to break these bonds. Secondly, they don't have any dipoles meaning they can only form london forces which are realitvely weak.
• However, what type of reaction can alkanes take part in? What is made in these reactions?

  They can take part in addition reactions.

  When alkanes react with chlorine or bromine, haloalkanes are made, such as bromoethane.
• What are the key conditions required for substitution reactions to occur?

  • the reaction cannot occur in the dark
  • the reaction can occur at room temperature at exposure to UV light.
• What are the observations that can be made from addition reactions?

  Bromine is decolorised (Br2 is orange, but the products are colourless.)

  Steamy, acidic HBr fumes are produced.
• When pentane undergoes monobrominisation, what are the three structural isomers that can be made? (THESE ARE ALL CALLED ISOMERIC BROMOALKANES OF ONE ANOTHER).

  1 bromopentane

  2 bromopentane

  3 bromopentane
• When doing these substitution reactions, you can control the yield received by what the excess product you put in is going to be.

  For example, a large excess of CH4 results in CH3Cl as main organic product

  But a large excess of Cl2 or Br2 results to a high yield of CCl4 or CBr4.
• A reaction of an alkane with chlorine and an alkane with bromine is very similar, but the reaction with chlorine is more vigorous.