AlKENES

• Alkenes


  Unsaturated hydrocarbons containing a carbon-carbon double bond
• Carbon-carbon double bond in alkenes

  • Area of high electron density
  • Consists of a normal covalent bond and a π bond
• Bromine water


  • Turns from orange-brown to colourless if a double bond is present
• Electrophiles


  Electron acceptors attracted to areas of high electron density
• Common electrophiles


  • HBr
  • Br2
  • H2SO4
• Electrophilic addition


  Reaction mechanism showing how electrophiles attack the double bond in alkenes
• Carbocation


  Carbon atom with only three bonds, meaning it has a positive charge
• Carbocation stability


  • Tertiary most stable, primary least stable
  • More stable carbocation more likely to form
  • Major product will be the most stable possible
• Mechanism for halogenoalkanes


  Bromine molecule gains temporary dipole so electrons are transferred
• Mechanism for sulphuric acid


  Alkene reacts with sulphuric acid to produce ethyl hydrogensulphate
• Addition polymers


  Produced from alkenes where the double bond is broken to form a repeating unit
• Repeating unit in addition polymers

  • Shown with extended bonds through the brackets
• Reaction conditions for addition polymers

  • High pressures and temperatures produce branched chain polymers with weak intermolecular forces
  • Lower pressures and temperatures produce straight chain polymers with strong intermolecular forces
• Uses of polymers

  • Unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds, useful for manufacturing many everyday plastic products
  • Unreactive nature means they are not biodegradable and cannot be broken down by species in nature
• PVC (Poly(chloroethene))


  Addition polymer with waterproof properties gained by addition of plasticisers