haloalkanes

• What are haloalkanes?

  saturated organic compounds that contain carbon atoms and at least one halogen atom
• Are halogenoalkanes soluble in water?

  no, they are insoluble in water

  this is because C-H bonds are non-polar, not compensated for enough by C-X bond polarity
• Do halogenoalkanes have a polar bond?

  yes

  as a halogen has a higher electronegativity than carbon

  halogen is &-

  carbon is &+
• What type of IMF do haloalkanes have, why?

  permanent dipole-dipole interactions as C-X bond polarity creates permanent dipoles

  london dispersion forces
• When do halogenoalkanes have higher boiling points?

  when the carbon chain length is increased

  contains a halogen further down group 7
• What would bond polarity suggest the order of reactivity would be?

  C-F would be most reactive as most polar bond
• What would bond enthalpies suggest the order of reactivity would be?

  C-I would be most reactive as lowest bond enthalpy
• What is a primary halogen?

  the halogen is present at the end of the chain
• What is a nucleophile?

  electron pair donor
• What are 3 nucleophiles?

  :OH-

  :CN-

  :NH3
• What is nucleophilic substitution?


  a reaction where a nucleophile donates a lone pair of electrons to the partially positive C atom

  the partially negative atom leaves the molecule and is replaced by the nucleophile
• What is hydrolysis?

  a reaction where water is a reactant
• What fission does water undergo to produce OH-?

  heterolytic fission
• What are CFCS?


  chlorine-fluoro-carbons

  haloalkanes containing C, F and Cl only (no H)
• What is the problem with CFCs?

  although unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution
• What is the main function of the ozone layer?

  provides protection from harmful UV radiation
• Does ozone play a protection role in all layers of the atmosphere?

  no, in the troposphere it contributes towards photochemical smog
• How do CFCs break down the ozone layer?

  free radical substitution
• What is the equation for the overall decomposition of ozone into oxygen (O2)?

  2O3 -> 3O2
• What are the free radical substitution equations to show how Cl free radicals catalyse the decomposition of O3?

  1 Cl2 -> 2Cl.

  2a Cl. + O3 -> ClO. + O2

  2b ClO. + O3 -> Cl. + 2O2
• What are properties of CFCs?

  chemically inert

  non-flammable

  non-toxic
• How are CFCs responsible for breaking down the ozone layer?

  • CFCs are broken down by UV radiation in the upper atmosphere, producing chlorine radicals in an initiation step
  • Chlorine radicals react with ozone, breaking it down
  • Chlorine radicals catalyse the reaction as they are regenerated in the second step of the reaction and can go on to break further ozone molecules down
• What are haloalkanes?

  a family of compounds which have had one or more hydrogen atoms in an alkane replaced by a halogen atom (these are also referred to as halogenoalkanes by some exam boards and some resources refer to them as alkyl halides)
• What are organohalogen compounds?

   a group of compounds that contain at least one halogen atom joined to a carbon atom. They have many uses but do not break down easily so are cause for environmental concerns.
• How do haloalkanes produce alcohols?

  Alcohols are formed from haloalkanes in a hydrolysis reaction where the halogen atom is replaced by an -OH group, which acts as the nucleophile. This reaction is an example of nucleophilic substitution.

  The haloalkane is heated with an aqueous solution of sodium hydroxide or potassium hydroxide with ethanol.