addition reactions of alkenes

• electrophiles are electron pair acceptors
• nucleophiles are electron pair donors
• electrophilic addition reactions

  • in addition reactions, two or more molecules become bonded to make one product
  • for alkenes , the pi bond + a small molecule is added across the two carbon atoms to make a saturated organic product
• Hydrogenation

  addition reaction where H atoms are added

  • at 150 degrees, with a suitabble catalyst like nickel, gaseous hydrogen + an alkene mixed
  • passed over a catalyst in a reactio chamber

  ALKENE + H2 - Nickel 150 -> ALKANE
• Halogenation

  addition reaction where halogen atoms are added, producing dihalogenalkane -> saturated

  • can be used to test for saturation

  when bromine solution or iodine solution is mixed with a saturated compound there is no reaction. However, when either reacts with an unsaturated compound decolourisation results because an addition reaction occurs.
• table 1
• Hydration

  addition reaction between gaseous alkene + steam

  conditions :

  • steam in the presence of an acid catalyst, usually phosphoric acid
• Addition of hydrogen halides

  addition reaction in which a hydrogen halide is added across the C=C bond

  • this produces a class of compounds called haloalkanes
  • these are saturated organic compounds based on alkane chain skeletons - at keast one hydrogen is replaced by a halogen atom
  • Hydrogen halides are gases at room temperature. These reactants are bubbled through the alkene to cause a reaction
• reaction mechanism is a model that shows the movement of electrons in an orgaanic reaction