Alkenes

• What is the double covalent bond in alkenes a centre of?

  high electron density
• What is an electrophile?

  An electrophile is a chemical species that accepts an electron pair and is attracted to an area of high electron density
• What is the positive test for alkenes?

  bromine water decolourises
• What happens to the reacitivity of alkenes with halogens?

  decreases as the larger molecules less polarised by carbon double bond
• What happens to the rate as you go from HF-HI when reacting with alkenes and why?

  Increases as the strength of the hydrogen and halogen bond decreases so more easily broken
• What happens to the rate when you change the alkene when reacting with hydrogen halides?

  increases
• Why does rate of reaction increase when alkenes become more complicated when reacting with hydrogen halides?

  Alkyl groups push electrons towards carbon double bond making it a higher region of electron density

  More stable intermediate
• What is the rule for identifying the major products when unsymmetrical alkenes react with hydrogen halides?

  hydrogen becomes attached to carbon with the most hydrogen attached to it already
• Name the one case where Markovnikovs Rule is an exception?

  if hydrogen bromide and alkene contain traces of organic peroxides
• Explain why there is an attraction between carbon double bond and Br2?

  carbon double bond is an area of high electron density

  Br-Br becomes polarised

  delta positive Br attracted to carbon double bond
• A carbocation in which the positive carbon has one alkyl neighbour is called a?

  primary carbocation
• A carbocation in which the positive carbon has two alkyl neighbour is called a?


  secondary carbocation
• A carbocation in which the positive carbon has three alkyl neighbour is called a?

  tertiary carbocation
• What is the product formed when alkenes react with concentrated sulfuric acid?

  alkyl hydrogensulfate
• How can alkyl hydrogensulfate be turned into an alcohol?

  React with water and distill
• Why are plasticisers added to polymers?

  makes them more flexible and reduces melting point
• What are the conditions, mechanisms, and properties of the synthesis of LDPE?

  High temperatures and pressure

  Free radical mechanism

  Branched chains

  Low density
• What is LDPE used in?

  plastic bags and electrical cable insulation
• What are the conditions needed for the synthesis of HDPE?

  Temperature just above room temperature and pressure just above atmospheric

  Ziegler Natta catalyst

  Less branching

  High density
• What are the 2 ways in which plastics are recycled?


  mechanical

  feedstock
• What is a limitation of mechanical recyling?

  limited number of products can be produced
• What is a limitation of feedstock recycling?

  Can only be done a few times before polymer biodegrades
• Give one use of HDPE?

  Buckets
• Give one use of PVC?

  drainpipes and window frames