Alkenes

• What type of bond prevents rotation in alkenes?

  Carbon-carbon double bond
• Why can the carbon-carbon double bond not rotate?

  Pi bond causes restricted rotation
• What is a position isomer in alkenes?

  Double bond in different positions
• What is stereoisomerism in alkenes?

  Same structural formula, different atom arrangement
• What phrase helps determine E or Z isomers?

  Priority groups are on the 'Zame Zide'
• Are alkenes soluble in water?

  No
• Why do we get major and minor products in alkene reactions?

  Major product forms on more stable carbocations
• What is produced when an alkene reacts with steam under a phosphoric acid catalyst?

  Alcohol
• What is a polymer?

  A chain of monomers
• Why are alkenes and alkanes not biodegradable?

  They are extremely unreactive
• How do we produce low density polyethene?

  Polymerising ethene at high pressure and temperature
• What is the result of polymerising ethene at high pressure?

  Produces branched polymers that are stretchy
• How do we produce high density polyethene?

  Using room temperature and a Ziegler-Natta catalyst
• What is the characteristic of high density polyethene?

  Less branched and can pack together
• What are the two methods of recycling plastics?

  • Mechanical recycling:
  • Separate, wash, sort, grind, melt, remake
  • Feedstock recycling:
  • Heat plastics to break polymer bonds, produce monomers
• What happens to polymer chains in feedstock recycling?

  Chains become shorter and lose properties
• What is an electrophile?

  An electron pair acceptor
• Why can alkenes undergo addition reactions?

  They are unsaturated
• Why are electrophiles attracted to the carbon-carbon double bond?

  Area of high electron density
• Why do we get major and minor products in electrophilic addition reactions?

  Secondary and tertiary carbocations are more stable than primary ones
• Explain why there is an attraction between c=c and br-br

  • c=c is electron rich
  • Br-Br becomes polarised
  • Delta positive region of br-br is attraction to electron rich area of c=c
• Why are plasticisers added to molecules?

  To make them more flexible
• Why is more of isomer E formed than isomer F?

  • E is formed via more stable carbocation
  • Secondary carbocation more stable than primary carbocation
• Whats the test for unsaturated alkenes?

  Decolourises bromine water from reddish-brown to clear
• How may we obtain three isomers from an electrophilic addition reaction?

  • Two exist as enantiomers
  • One is formed as the minor product via the primary carbocation
• What are the conditions for an electrophilic addition reaction with sulfuric acid?

  • Concentrated sulfuric acid
  • Room temperature
• How can we convert the products of an electrophilic addition reaction with conc sulfuric acid to an alcohol?

  Add water

  Produces an alcohol

  Acid acts as a catalyst
• What happens when monomers polymerise?

  Double bond opens
• How do we represent addition polymers?

  $-\left[CH2-CH2\right]-_n$
• What are the typical uses of PVC?

  Aprons, vinyl records, drainpipes
• Why are polymers unreactive?

  • C-C backbones
  • Strong non-polar C-H bonds
• Why would PVC not react with bromine water?

  It is saturated
• E-Z isomers form the same....


  Repeating unit
• What are more stable, E or Z isomers? Why does this isomerism arise?

  E are more stable

  C=C bond cannot rotate

  Each carbon in the double bond has two different groups attached