chem unit 1

• Alkenes


  Unsaturated hydrocarbons with at least one carbon-carbon double bond
• Homologous series of alkenes


  • C​n​H​2n
• Cycloalkenes


  Type of alkene hydrocarbon where the carbon atoms are arranged in a closed ring
• Carbon double bond


  • Area of high electron density making it susceptible to attack from electrophiles
  • Consists of a normal covalent σ bond and a π bond
• Bromine water test


  • Used to identify an alkene double bond and other unsaturated compounds
  • Alkenes cause bromine water to change colour from orange-brown to colourless
• Stereoisomers


  Have the same structural formula but different spatial arrangement of atoms and bonds
• 1. Z isomerism


  Type of stereoisomerism that occurs due to the limited rotation around a double carbon bond
• E isomer


  Groups attached to the C=C are apart
• Z isomer


  Groups attached to the C=C are together on the same side
• Cahn-Ingold-Prelog (CIP) priority rules


  Used to determine if a molecule is the E or Z isomer based on the priority of different groups
• Cis- and trans- isomers

  Stereoisomers named based on whether the groups are on the same side or different sides, when there are hydrogen atoms present
• Electrophilic addition


  Double bond opens up to form single bonds to other atoms
• Alkanes


  Formed when alkenes undergo electrophilic addition with hydrogen, requiring a nickel catalyst
• Halogenoalkanes


  Formed when alkenes undergo addition reactions with halogens or hydrogen halides
• Alcohols


  Formed when alkenes undergo addition reactions with steam, requiring an acid catalyst
• Diols


  Alcohols with two hydroxyl functional groups, formed by oxidation of alkenes with acidified potassium manganate(VII)
• Common electrophiles


  • HBr
  • Br​2
  • H​2​SO​4
• Electrophilic addition mechanism: Alkene + Halogen


  Bromine molecule gains a temporary dipole, electrons are transferred, forming a dihalogenoalkane
• Electrophilic addition mechanism: Alkene + Hydrogen Halide

  Hydrogen halide is polar, the electron pair in the double bond attracts H​δ+​, forming a carbocation intermediate which attracts the halide ion
• Inductive effects of alkyl groups

  Carbocations with more alkyl groups are more stable due to the positive inductive effect, making them the major product
• Addition polymers


  Produced from alkenes, where the double bond is broken to form a repeating unit
• Monomers


  Short chain alkenes that join together to form long chain polymers
• Repeating unit

  Must be shown with extended bonds through the brackets, bonding to other repeating units on both sides
• Polymers


  • Unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds, making them useful for manufacturing many everyday plastic products
  • Not biodegradable and cannot be broken down by species in nature
• Disposal methods for polymers


  • Recycling
  • Using as feedstock for cracking
  • Incineration to produce energy, but can release toxic gases
• Scientists are developing biodegradable polymers to overcome the various disposal issues