reactions of alkenes

• Alkenes


  Unsaturated hydrocarbons that contain at least one carbon-carbon double bond
• Alkenes


  • They can undergo addition reactions due to their carbon-carbon double bond
• Addition reactions of alkenes

  1. Double bond opens up

  2. Atoms of another molecule bond to the carbons
• Types of addition reactions of alkenes

  • With hydrogen
  • With water
  • With halogens
• Reaction of alkene (propene) with hydrogen

  1. Double bond breaks apart

  2. Hydrogen atoms bond to the carbons

  3. Product is propane (saturated alkane)
• Reaction of alkene (ethene) with water

  1. Double bond opens up

  2. Water molecule splits into H and OH

  3. H and OH bond to the carbons

  4. Product is ethanol (alcohol)
• Ethanol is the same alkyl used in alcoholic drinks and some industrial processes
• Separating ethanol and water after reaction

  1. Ethene has low boiling point, stays as gas

  2. Water and ethanol condense as liquids

  3. Fractional distillation separates water and ethanol
• Reaction of alkenes with halogens (e.g. bromine)

  1. No catalyst required

  2. Bromine reacts with alkene to form dibromoalkane

  3. Bromine colour disappears
• Alkenes can decolorize bromine water


  Alkanes cannot
• This bromine test is used to distinguish alkenes from alkanes
• Alkene


  A molecule with a carbon-carbon double bond
• Alkenes


  • Unsaturated
  • Double bond can break into a single bond, allowing new bonds to form
• Addition polymerization of alkenes

  1. Monomers (e.g. ethene) form new bonds with each other

  2. Resulting in a long chain polymer
• Monomer


  The smaller units that make up a polymer
• Repeating unit


  The group of atoms that is repeated throughout the polymer, containing the same atoms as the monomer
• To draw the reaction, show a single monomer on the left and a single repeating unit on the right</b>
• Bonds of the monomer should be drawn facing up and down, while bonds of the repeating unit should point left and right through the brackets
• The 'n' represents the number of monomers and repeating units in the polymer
• Butane


  A 4-carbon alkene
• Drawing the monomer of butane

  1. Identify the double bond

  2. Rearrange the groups attached to the double-bonded carbons to be above and below

  3. Simplify the larger group to C2H5
• The bonds in the repeating unit extend through the brackets
• Polymer naming


  Poly + monomer name (e.g. polybutane, polyethylene, polychloroethylene)
• Addition polymerization requires high pressure and a catalyst