10.2 Functional group chemistry

  1. Alkanes
    1. Combustion
      1. Alkanes undergo complete combustion in presence of excess oxygen
      2. Alkanes undergo incomplete combustion in limited supply of oxygen (producing carbon monoxide or even just carbon atoms)
    2. Halogenation (Substitution and elimination. Free radical substitution)
      1. Alkanes undergo freeradical substitution and elimination to form unsaturated alkenes and alkynes
    3. Free-Radical substitution
      1. Occurs in presence of UV light
      2. Free-radical refers to species formed when molecule undergoes homolytic fission
      3. Homolytic fission: The two electrons of a covalent bond are split evenly between two atoms resulting in two free-radicals that each have a single electron
      4. Heterolytic fission: The bond creates a cation and an anion because the electrons are unevenly split (both electrons go to one atom)
      5. There are three steps involved in free-radical substitution reaction between methane and chlorine:
        1. Initiation: The homolytic fission of the chlorine molecule in the presence of UV light.
        2. Propagation: The radicals react with neutral atoms in attempt to gain stability. The target neutral atom then becomes a radical in the process.
        3. Termination: Radicals join together creating new compounds in the process. This occurs either when:
          1. Emission of UV light is stopped preventing creation of radicals
          2. Concentration of hydrocarbons decrease because they “mop up” the radicals
  1. Alkenes
    1. Hydrogenation
        • Alkenes undergo addition reactions
        • A mixture of alkene and bromine water will undergo a colour change from brown to colourless. This indicates the presence of unsaturated moleculesAlkene_to_alkane
    2. Halogenation
      1. Electrophilic halogenation of symmetrical alkenes involves addition of elemental halogens resulting in dihalogenated alkaneHalogenation
      2. Addition of hydrogen halide (HX) to a symmetrical alkene results in single mono-halogenated alkaneHalogenation 2
      3. (Addition to Asymmetrical alkenes is covered in topic 20.1)
    3. Polymerization
      1. Addition polymerization is the reaction of many small monomers that contain carbon-carbon double bond, linking together forming a polymerPolymerization
  1. Alcohols
    1. Can undergo complete combustion releasing CO2 and H2O
    2. Oxidation
      • Oxidation of primary alcohols is a two step process
      • The oxygen donor [O] is normally acidified K2Cr2O7
      • Primary Alcohols:
      • Oxidation
      • Secondary Alcohols:Secondary Alcohol
    3. Condensation
      1. Between alcohol and carboxylic acid
        1. The catalyst used is normally H2SO4
        2. Esterification is a reversible processCondensation

Nucleophilic Substitution Reactions

  • Halogenoalkanes contain a polar carbon – halogen bond (C-X)
  • This electron deficient carbon is open to attack by electron rich species known as nucleophiles
  • Nucleophile contain a lone pair of electrons and sometimes have a full negative charge

Nucleophilic Substitution Mechanism

Electrophilic Substitution

  • Used for aromatic or compounds with double/triple bonds
  • Benzene does not readily undergo addition reactions. Instead, it undergoes electrophilic substitution reactions.
  • Electrophile is an electron poor species capable of accepting an electron pair
  • Arrows show movement of electrons

 Electrophillic Substitution

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