Alkenes

• What are alkenes?

  Unsaturated hydrocarbons that contain at least one C=C bond
• What is the general formula of alkenes?

  CnH2n
• How is a 𝜋 bond formed?

  Electrons in adjacent p orbitals overlap above and below the carbon atoms
• What bond restricts the rotation of carbon atoms?

  𝜋 bond
• What is the angle and shape of a double bond?

  Trigonal planar with an angle of 120°
• Are alkenes more or less reactive than alkanes? Why?

  More reactive due to high electron density of double bond
• What intermolecular forces of attraction do alkenes have?

  Only London forces due to non-polar bonds
• Are alkenes soluble in water? Why?

  No, due to non-polar bonds
• Write an equation for the complete combustion of pent-2-ene.

  CH3CH=CHCH2CH3 + 7½O2 → 5CO2 + 5H2O
• What are the types of isomers that can be formed using alkenes?

  E/Z isomers and cis-trans isomers
• What is an electrophile?

  Species that are electron pair acceptors
• What is the most stable type of carbocation intermediate? Why?

  Tertiary carbocation due to positive inductive effect of alkyl groups
• Major products will be formed from which kinds of carbocations?

  Tertiary (or the most stable available)
• What conditions are needed for the electrophilic addition of H2O to an alkene? What is this type of reaction called?

  Steam in the presence of an acid catalyst, called hydration
• What are the product(s) of the hydration reaction?

  An alcohol
• What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

  Hydrogen halide gases must be at room temperature
• What is the reaction called when a halogen is added to alkene?

  Halogenation
• How does a molecule with a non-polar bond react as if it is an electrophile?

  C=C double bond induces a temporary dipole in the halogen molecule
• How can an alkene be converted into alkane? What is the reaction called and what are the required conditions?

  Alkene + hydrogen = Alkane, called hydrogenation at 150°C with nickel catalyst
• What is an addition polymer?

  Many monomers bonded together without the loss of any atom or molecule
• What are monomers? What form do they usually take?

  Molecules which combine to form a polymer, usually with a C=C bond
• What are the ways in which plastics can be disposed?

  Landfill, combustion, electricity generation, reuse, recycle, organic feedstock
• What are the disadvantages of recycling?

  Plastics must be sorted, expensive, labor-intensive, requires high technology
• How do photodegradable polymers break down?

  They break down chemically using energy with wavelengths similar to light
• Explain what happens in organic feedstock.

  Plastics are separated and broken down into small organic molecules
• Give a disadvantage of photodegradable polymers.

  May not be exposed to sufficient light