chapter 15

• Haloalkanes have a carbo-halogen bond. The halogen is more electronegative than the carbon so the bond is polar
• Nucleophiles are a species that donate a lone pair of electrons. They are attracted to an electron deficient carbon atom in order to donate a pair of electrons
• When a haloalkane reacts with a nucleophile, the nucleophile replaced the halogen . This is called nucleophilic substitution
• Hydrolysis of a haloalkane is when the halogen is replaced by a oh group in nucleophilic substitution . This is done by the haloalkane reacting with aqueous sodium hydroxide heated under reflux
• The rate of hydrolysis depends on the strength of the carbon halogen bond. C-F is the strongest carbon halogen bond, and it decreases done the group.
• fastest- iodoalkanes

  Bromoalkanes

  Chloroalkanes

  slowest-floroalkanes
• Rate of hydrolysis increases as strength of carbon halogen bond decreases
• The ozone layer is being continually being formed and broken down by uv radiation

  O2 -> 2O: radicals

  O2 + O: -> O3 (ozone)
• Ozone absorbs most of the biologically damaging ultraviolet radiation, however CFCs have upset this
• CFCs are chlorofluorocarbons. They were used as refrigerants and aerosol. They are very stable due to the strength of the carbon halogen bonds
• They break down into chlorine radicals in the stratosphere and catalyse the breakdown of the ozone layer:

  Cl: +O3 -> ClO: + O2

  ClO: + O -> Cl: + O2
• Other radicals also catalyse the breakdown of ozone , including nit oxide radicals. They are formed during lightning strikes and aircraft travel

  NO: + O3 -> NO2: + O2

  NO2: + O -> NO: + O2