AS Chemistry A OCR - Haloalkanes

  • Created by: Shipreck
  • Created on: 11-02-16 23:49

Hydrolysis of Halogenoalkane by Aqueous Alkali

  • Nucleophile
    • A species that donates a pair of electrons.
  • Alkali
    • When added to water, OH- ions are formed.
    • Examples are NH3 and NaOH
  • Example:
    • The C-CL bond is polar.
    • The OH- Ion gives an electron pair to the carbon, forming a dative covalent bond.
    • The Cl atom takes the bonding electrons from the bond as it's more electronegative.
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Hydrolysis of Halogenoalkane by Water in the prese

  • Silver Nitrate
    • Creates Ag+ ions when in solution.
  • Ethanol and Water
    • Ethanol and Water used because everything is soluble in this solution.
  • You would have to keep the type of halogenoalkane (primary, secondary or tertiary) constant, but vary the halogen.
  • Halide Ions react with the Ag+ ion to form a precipitate.
    • The time taken for a precipitate of silver halide to appear will depend on how much of everything you use and the temperature at which the reaction is carried out. But the pattern of results is always the same.
  • A primary iodo compound produces a precipitate quite quickly.

  • A primary bromo compound takes longer to give a precipitate.

  • A primary chloro compound probably won't give any precipitate for many hours.

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Enthalpies of Carbon-Halogen Bonds

  • From the speed the Silver Halide forms we can determine the bond strength.
    • C-F is the strongest bond at ~485KJ per Mol
    • C-Cl is slightly weaker at ~330KJ per Mol
    • C-Br is slightly more weaker at ~285 KJ per Mol
    • C-I is even weaker at ~210 KJ Per Mol
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Chloro Flouro Carbons

  • Chloro Flouro Carbons (CFC's) contain no hydrogen molecules.
  • Benifits of CFC's
    • Unreactive
    • Unflammable
    • Nonetoxic
  • CFC's were used very commonly in aerocells. 
  • CFC's are catalysts in ozone (O3) depletion.
  • The steps
    • When the CFC's reach the ozone layer, because of UV light, the C-Cl Bond breaks homolytically and creates two radicals.
    • The Cl radical then reacts with an ozone molecule, creating ClO radical and O2.
    • The ClO radical reacts with an oxygen atom, creating Cl radical and O2.
  • Because of this , CFC's are banned from commercial use, and are limited to only highly restricted industrial use.
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Nitrogen Monoxide and Ozone

  • Nitrogen Monoxide is another radical that catalyses ozone depletion.
  • Nitrogen Monoxide is created by lightning strikes.
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