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Halogenoalkanes

AQA AS-level ChemistryTopic 13 of 1616 lessons

Revision notes for Halogenoalkanes in AQA Chemistry (7404). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. General FormulaHalogenoalkanes are alkanes in which one or more hydrogen atoms have been replaced by halogen atoms.
  2. Naming HalogenoalkanesHalogenoalkanes are named using a prefix for the halogen: fluoro-, chloro-, bromo- or iodo-, added to the name of the parent alkane.
  3. Bond PolarityHalogens are more electronegative than carbon, so the carbon-halogen bond in a halogenoalkane is a polar bond.
  4. Physical PropertiesThe boiling point of a halogenoalkane depends mainly on the strength of the van der Waals forces between its molecules.
  5. Reactivity of the Carbon-Halogen BondHalogenoalkanes react when the carbon-halogen bond breaks.
  6. NucleophilesA nucleophile is an electron pair donor.
  7. Nucleophilic SubstitutionIn nucleophilic substitution a nucleophile replaces the halogen atom in a halogenoalkane.
  8. Reaction with Aqueous Sodium HydroxideHalogenoalkanes react with warm aqueous sodium hydroxide to form alcohols.
  9. Reaction with Cyanide IonsHalogenoalkanes react with potassium cyanide dissolved in aqueous ethanol to form nitriles.
  10. Reaction with AmmoniaHalogenoalkanes react with ammonia to form primary amines.
  11. Uses of Nucleophilic SubstitutionNucleophilic substitution is useful in organic synthesis because it swaps the halogen for a new functional group.
  12. Elimination ReactionIn an elimination reaction a halogenoalkane loses a molecule of hydrogen halide (HX) and forms an alkene.
  13. Mechanism of EliminationThe elimination mechanism is shown with three curly arrows.
  14. Conditions for Substitution vs EliminationHydroxide ions can react with halogenoalkanes by nucleophilic substitution or by elimination.
  15. Classification of HalogenoalkanesHalogenoalkanes are classified as primary, secondary or tertiary.
  16. Chlorofluorocarbons and the EnvironmentOzone, O3, in the upper atmosphere absorbs much of the Sun's harmful ultraviolet radiation, which can cause skin cancer and cataracts.

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