4.2.2 - haloalkanes

• Haloalkanes are saturated organic compounds that contain carbon atoms and at least one halogen atom
• A primary haloalkane is when the halogen atom is at the end of the chain / when the carbon the halogen is attached to is attached to one other carbon
• A secondary halogen is when the carbon the halogen is attached to is attached to two other carbons
• A tertiary halogen is when the carbon the halogen is attached to is attached to three other carbons
• Halogenalkanes are insoluble in water because C-H bonds are non-polar and this outweighs the polar C-X bond
• Carbon halogen bonds are polar because the halogen is very electronegative so is §- making the carbon §+
• Haloalkanes have london forces
• Boiling point of haloalkane increases as halogen is further down group 7 because there are more electrons and therefore more london forces.
• Mass of haloalkanes are higher than mass of equivalent straight chain alkane as the halogen has a greater mass than hydrogen
• Strength of carbon halogen bond determines the halogen reactivity
• C-I is the most reactive haloalkane because it has the lowest bond enthalpy
• A nucleophile is an electron pair donor
• 3 examples of nucleophiles are:

  :OH-

  :CN-

  :NH3
• nucleophilic substitution is where a nucleophile donates a lone pair of electrons to a §+ carbon atom

  the §- atom leaves the molecule and is replaced by nucleophiles
• Hydrolysis is a reaction where water is a reactant
• Water undergoes Heterolytic fission to produce OH- ions
• CFCs are chlorofluorocarbons

  haloalkanes containing C, F and Cl only
• CFCs when exposed to UV light catalyse the breakdown of ozone in the atmosphere via free radical substitution
• The ozone layer provides protection from harmful UV radiation
• Ozone layer contributes to photochemical smog in the troposphere
• The overall equation for the breakdown of ozone into oxygen is:

  O3 + O ——> 2O2
• The free radical substitution equations for Cl radicals catalysing ozone breakdown are:

  Cl2 ——> 2Cl .

  Cl . + O3 ——> ClO . + O2

  ClO . + O ——> Cl. + O2
• The producers of nitrogen oxides in the atmosphere are:

  thunderstorms

  Lightening

  aircraft
• The free radical substitution for nitrogen monoxide decomposing ozone is:

  NO + O3 ——> NO2 + O2

  NO2 + O ——> NO + O2