Topic 4 Alkenes

• What is the general formula for alkanes? [1]

  CnH2n
• Alkenes are all unsaturated
• Alkenes have high electron density
• Define electrophile [2]

  Electrophile are electron pair acceptors - they’ll usually short of electrons so are attracted to areas filled with electrons
• Cold concentrated sulphuric cid reacts with an alkanes in electrophilic addition. Then add cold water and warm the products, it hydrolyses to form an alcohol. The sulphuric cid acts as a catalyst
• What is the test for unsaturation? [3]

  When you shake an alkanes with orange bromine water, the solution quickly decolourises. Bromine is added across the c+c double bond to form colourless dibromoalkane
• For addition of alkenes, two products can be formed and that is dependent on how stable the carbocation is.
• If a product of addition has more alkyl groups, the more stable the carbocation will be. The more stable the more likely it is to form
• What is the order of stability of carbocations? [3]

  primary<secondary<tertiary

  least stable. most stable
• edition reactions occur when a hydrogen halide adds to an unsymmetrical alkene
• What is an addition polymer? [1]

  It is when an alkene can act as a monomer to form polymers as they can open up and join together to make long chains
• Why are addition polymers very unreactive? [2]

  Polyalkene chains are saturated molecules it is also non polar
• What are the properties of an addition polymer? [3]

  Non-polar

  Held together by van der waals forces

  Longer the chains and the closer together they are means the stronger the forces
• What are polyalkenes made up of? [2]

  short branches chains and tend to be weaker and more flexible
• What are plasticsers? [2]

  Makes polymers more flexible. the plasticer molecules get between the polymer chains and push them apart. This reduces the strength of the intermolecular forces between the chains, making them easier to bend
• PVC is hard and brittle at room temperature. Rigid PVC is used to make drainpipes and window frames. Plasticised PVC is flexible and is used to make electrical cable insulation, flooring tiles and clothing