Haloalkanes

• Define Haloalkanes:

  A compound that contains a halogen atom and an alkane group
• Halogenoalkanes are classified as:

  • Primary
  • Secondary
  • Tertiary
• In a carbon-halogen bond, the halogen is slightly more negative and the carbon is slightly more positive
• Name the intermolecular forces in Haloalkanes:

  • London forces
  • Permanent dipole-dipole interactions
• Haloalkanens have a higher boiling point as...

  • the chain length increases
  • you go down group 7
• Define Nucleophile:

  An electron pair donor
• Polarity of carbon-halogen decreases as you go down group 7
• Polarity of carbon-halogen increases as you go up group 7
• The greater the Mr of the halogen in the carbon-halogen bond, the lower the bond enthalpy
• The greater the Mr of the halogen in the carbon-halogen bond, the lower the bond enthalpy
• The rate of reaction for haloalkanes increases as you go down group 7
• Water is a nucleophile but it reacts too slowly
• What are nucleophiles attracted to?

  electron deficient atoms / low electron density
• Name the mechanism that describes haloalkanes reacting with a nucleophile?

  Nucleophilic substitution
• In the hydrolysis of a halogenoalkane, the halogen atom is replaced by an - OH group
• Haloalkanes are hydrolysed to produce alcohols
• State the two possible reagents used in the hydrolysis of haloalkanes to produce alcohols:

  • water
  • warm aqueous alkali
• Name the products of the hydrolysis of halogenoalkane with warm aqueous alkali:

  • alcohol
  • halide ion
• State the condition for the hydrolysis of haloalkanes:

  • Under reflux
• Why is the hydrolysis of haloalkanes performed under reflux?

  • to maximise the yield
• What does the rate of reaction of the hydrolysis of haloalkanes depend on?

  the bond enthalpy of the carbon-halogen bond
• Name the products of the hydrolysis of halogenoalkane with water:

  • alcohol
  • halide ion
  • hydrogen ion
• Which halogenoalkane is considered to be unreactive?

  Fluoroalkanes
• Haloalkanes are insoluble in water
• What is added to the sample for the test for halogens?

  • ethanol
  • aqueous silver nitrate
• Why is ethanol added to the test for halogens?

  it allows water and the halogenoalkane to mix and produce a single solution rather than two layers
• Why is aqueous silver nitrate added to the test for halogens in haloalkanes?

  the halide ions react with the silver ions to form a coloured precipitate of silver halide
• Tertiary haloalkanes are hydrolysed the fastest, primary haloalkanes are hydrolysed the slowest
• Tertiary haloalkanes are hydrolysed the fastest, primary haloalkanes are hydrolysed the slowest
• Give the formula for three nucleophiles:

  • OH-
  • CN-
  • NH3
• Define Chlorofluorocarbons: (CFCs):

  Compounds containing only chlorine, fluorine, and carbon atoms
• Name this CFC:

  trichlorofluoromethane

  
• Name this CFC:

  chlorotrifluoromethane

  
• Features of Chlorofluorocarbons (CFCs):

  • non-flammable
  • non-toxic
  • inert
  • stable
  • volatile
• Define The Ozone layer:

  A high concentration of ozone molecules in a layer of the stratosphere of the earth's atmosphere that absorbs ultraviolet radiation from the sun
• What is the disadvantage of CFCs?

  they catalyse ozone depletion in the atmosphere via radical substitution
• Define Organohalogens:

  Compounds that contain at least one halogen atom
• Through what type of reaction do ozone molecules form?

  Radical substitution
• What is the main function of the ozone layer?

  to provide protection from ultraviolet (UV) radiation
• What is the disadvantage of the ozone layer for other layers of the atmosphere?

  it contributes towards photochemical smog in the troposphere layer