Alkenes

• Unsaturated hydrocarbons?


  Contain c=c bonds and only contain c-h atoms.

  CnH2n
• Physical properties?

  Insoluble as similar electronegativity between c-h.

  Double bond has restricted rotations so fixed shape and orientation.
• Reactivity?


  Too valuable to burn and burn with sootier flame. Double bond is very reactive as electron rich.

  Alkenes + water > alcohol (high temp/pressure H3PO4 catalyst)
• Electrophilic addition?


  Electrophile- negative seeking. Lone pair acceptor.

  Tertiary carbocation is most stable as 3 alkyl groups push electrons towards carbocation.
• Testing for alkenes?


  Add bromine water and it should go from orange > colourless.
• Polymer types?


  Natural- starch, proteins, cellulose, DNA.

  Synthetic- Plastics, fibres.
• Addition polymerisation?


  Alkene > polyalkane.

  
• Properties of polymers?


  Plasticisers- Small molecules that get between polymer chains allowing them to slide over eachother. (make them flexible)

  PVC- made into chain pipes or aprons using plasticisers.
• Polythene?


  High density:

  Strong, higher bp/mp

  Forms with low temp/pressure, ziegler catalyst.

  eg buckets, bottles.

  Low density:

  Flexible and stetchy.

  Forms in high temp/pressure. Chains are branched.

  eg plastic bags, electrical insulators.
• Biodegradability?


  Ability to breakdown polymer via biological agents eg water, enzymes.

  Polymers are saturated, unreactive and non-polar.

  You can either burn them or dispose in landfill.
• Environmentally friendly disposal?


  Mechanical: Sort, wash, ground into pellets, melted, remoulded.

  Feedstock: Heat, reproduce monomers, recombine.

  Repeated heating/melting can damage chains, degrading plastic properties.
• what is an alkene?

  unsaturated hydrocarbons with c=c double bond
• general formula for alkene?

  CnH2n
• why is there no rotation around c=c bond?

  due to pi orbital as electron density is above and below bond which holds carbon atoms in place
• are alkenes more or less reactive than alkanes?

  More due to higher electron density of double bond
• what is an electrophile?

  electron deficient atoms which accept a pair of electrons
• what is the most stable carbocation intermediate?

  alkyl groups have a positive inductive effect.

  Tertiary are most stable as bonded to most other carbon atoms
• mechanism for addition of water to ethene?

  electrophilic addiciton

  
• how does a molecule with a non polar bond react as an electrophile?

  c=c bond induces a temporary dipole in the halogen molecule.
• mechanism for reaction of bromine with ethene?

  electrophilic addition

  
• mechanism for reaction of sulfuric acid with butane?

  electrophilic addition

  
• what is an addition polymer?

  many monomers bonded together via rearrangement of bonds
• what are monomers?

  molecules which combine to form a polymer
• draw the polymerisation of ethene?

  ta da

  
• give uses of PVC? poly(chloroethene)

  drain pipes

  vinyl

  aprons
• example of plasticiser?

  ester
• what are plasticisers?

  small molecules that get between polymer chains to force them apart and allow them to slide over eachother
• what is mechanical recycling?

  plastics are separated into dif types, washed, ground down, melted and re-moulded
• what is mechanical recycling used for?

  soft drink bottles

  fleeces
• what is feedstock recycling?

  plastics heated to a temp which breaks polymer bonds, leaving original monomers can made into new plastics
• problem with recycling?

  each time plastics are melted and remoulded, properties degrade