Haloalkanes

• Prefixes


  Fluoro,chloro,bromo,iodo
• Classification


  Primary - one carbon attached to the C-X bond

  Secondary- two carbon attached to the C-X bond

  Tertiary- three carbon attached to the C-X bond
• Haloalkane reactions


  Either undergo elimination or substitution reactions
• Substitution


  swapping a halogen atom for another atom/ groups of atoms
• Nucleophile


  Electron pair donator - makes bonds
• :Nu


  Represents any nucleophile - they always have a lone pair
• Curly arrow


  Will always start from a lone pair of electrons or the centre of a bond
• Rate of substitution reactions

  Depends on the strength of the C-X bond

  The weaker the bond, the easier it is to break and faster the reaction
• Fastest to slowest


  Iodoalkanes are the fastest to substitute and the fluoroalkanes are the slowest.
• Hydrolysis


  The splitting of a molecule (in this case a haloalkane) by a reaction with water
• Water is …


  a poor nucleophile but it can react slowly with haloalkanes in a substitution reaction
• Nucleophilic substitution with aqueous hydroxide

  Change in funct group - alcohol

  Reagent - potassium/ sodium hydroxide

  Conditions - aqueous solution and heat under reflux
• Nucleophilic substitution with cyanide ions

  Change in funct group - nitrile

  Reagent - KCN dissolved in ethanol/water mixture

  Conditions - heating under reflux
• Nucleophilic substitution with ammonia


  Change in funct group - amine

  Reagent - NH3 dissolved in ethanol

  Conditions - heated under pressure
• Why excess ammonia?


  Further substitution reactions can occur between between the haloalkanes and the amines formed leading to a lower yield of the amine.

  Using excess ammonia helps minimise this
• Elimination reaction


  Removal of small molecule (often water) from the organic molecule

  Always with a hydroxide iom
• Elimination with alcoholic hydroxide ions

  Change in funct group - alkene

  Reagents - Potassium/sodium hydroxide

  Conditions - in ETHANOL, heated
• Importance of the solvent

  Aqueous- substitution

  Alcoholic- elimination
• How the structure of the haloalkane affects the reaction

  Primary haloalkanes tend towards substitution

  Tertiary haloalkanes tend towards elimination
• Ozone layer


  Naturally occuring in the upper atmosphere is beneficial as it filters out much of the sun’s harmful UV radiation
• Effect of CFC on ozone


  Man made CFCs cause a hole to form in the ozone layer
• Ozone in the lower atmosphere

  Is a pollutant and contributes to the formation of smog