Haloalkanes

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  • Created by: Siana
  • Created on: 11-02-14 19:33
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  • Haloalkanes
    • What is a Haloalkane?
      • Haloalkanes have an alkane skeleton with one or more halogen    
      • Fluorine, Chlorine, Bromine, or Iodine       
        • Replaces H atoms
    • General Formula
      • CnH2n+1X 
        • X is the Hydrogen
      • Shortened to R--X
    • Bond Polarity
      • Haloalkanes have a polar bond ( Co+-- Xo-)
      • As you go down the group of halogens they become less polar.
        • Electronegativity decreases
    • Physical Properties
      • Solubility
        • Not soluble in water
        • Intermolecular forces
          • Dipole-Dipole
          • V-D-W's
        • Mix with hydrocarbons
      • Boiling Point
        • B.pt increases with increased chain length
        • B.pt increases as we go down the halogen group
    • NUCLEOPHILIC SUBSTITUTION
      • These are reactions in which the bond between the carbon atom and the halogen atom breaks by HETEROLYTIC FISSION
      • When the bond breaks; one atom gets a lone pair of electrons, the other gets none.
        • Ions are formed
      • Rates of nucleophilic substitution
        • Depends on the halogen
          • F-C is the strongest - fluoroalkanes are lest reactive
          • Longer bonds = weaker bonds
        • Depends on the nature of the halogenoalkane
          • Order of reactivity: 3'>2'>1'
    • HYDROLYSIS using OH-
      • Hydroxide ion  acting as NUCLEOPHILE
      • Conditions
        • Aqueos ethanol (solvent)
        • KOH or NaOH (aq)
        • Room temperature
    • ELIMINATION using OH-
      • OH- acting as NUCLEOPHILE
      • Conditions
        • Dry ethanol (solvent)
        • Heat
    • ELIMINATION REACTIONS
      • Remove H and halogen (e.g. Br) from adjacent cations in a  halogenoalkane (alkanes)
      • Eliminated HBr is ACID
        • achieved using a strong  base
        • Hot, conc NaOH (ethanol) suitable
        • Converts HX to salt (NaBr) and water
    • FREE RADICAL SUBSTITUTION
      • INITIATION
        • U.V light breaks covalent bond (Cl--Cl) by homolytic fission producing 2 free radicals
      • PROPEGATION
        • A whole alkane or haloalkane reacts with a free radical to form another free radical - carrying on the reaction
      • TERMINATION
        • Two radicals react to form a whole alkane or haloalkane
      • CFC's and the OZONE layer
        • Ozone layer made up of O3
        • U.V. light breaks down CFC's to make free radicals
          • Cl. + O3 --> ClO. + O2
          • ClO. + O3 --> 2O2 + Cl.
          • Chlorine atoms catalyse the decomposition of ozone and contribute to holes in the ozone layer
        • Legislation to ban use of CFC's by chemists - developed chlorine-free compounds
        • Chloroalkanes/ chlorofluoro-alkanes can be used as solvents

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