Halogenoalkanes

• What are halogenoalkanes known for in chemistry?

  Different rates of substitution reactions
• Why can bond energies explain the reactivity of halogenoalkanes?

  Because breaking carbon-halogen bonds varies in energy
• What is the weakest carbon-halogen bond?

  • C-I bond
  • Requires the least energy to break
• How does the C-F bond compare to the C-I bond?

  C-F bond requires more energy to break
• What happens when halogenoalkanes react with aqueous silver nitrate?

  Formation of a precipitate occurs
• What does the rate of precipitate formation indicate?

  It indicates the reactivity of halogenoalkanes
• What is the fastest nucleophilic substitution reaction product?

  • Pale yellow silver iodide
  • Formed from iodoalkanes
• What is the slowest nucleophilic substitution reaction product?

  • Silver fluoride
  • Formed from fluoroalkanes
• Why are halogenoalkanes more reactive than alkanes?

  Due to the presence of electronegative halogens
• What causes the carbon-halogen bond to be polar?

  The large difference in electronegativity
• What are the two key types of reactions halogenoalkanes undergo?

  1. Nucleophilic substitution reactions
  2. Elimination reactions
• What is produced in nucleophilic substitution reactions of halogenoalkanes?

  Alcohols, amines, and nitriles
• What is eliminated during elimination reactions of halogenoalkanes?

  A hydrogen halide is eliminated
• What is the nucleophile in the formation of alcohols from halogenoalkanes?

  Hydroxide ion, OH^-
• Why is the reaction to form alcohols from halogenoalkanes slow at room temperature?

  Because it requires warming to proceed
• How does bond enthalpy affect the rate of hydrolysis of halogenoalkanes?

  Stronger C-X bonds lead to slower reactions
• What is the order of bond enthalpy for halogenoalkanes?

  C-F > C-Cl > C-Br > C-I
• Why do fluoroalkanes not react at all?

  They have the strongest C-F bond
• What is the better nucleophile, hydroxide ion or water?

  Hydroxide ion is the better nucleophile
• How can the rate of hydrolysis of halogenoalkanes be measured?

  Using acidified silver nitrate in test tubes
• What precipitates form from different halogenoalkanes in hydrolysis?

  • White precipitate from chloroalkane
  • Cream precipitate from bromoalkane
  • Yellow precipitate from iodoalkane
• Why does the yellow precipitate form the fastest?

  Because the C-I bond has the lowest bond enthalpy
• Why does the white precipitate form the slowest?

  Because the C-Cl bond has the highest bond enthalpy
• What is the nucleophile in the formation of nitriles from halogenoalkanes?

  Cyanide ion, CN^-
• What is the product formed when bromoethane reacts with potassium cyanide?

  Propanenitrile is formed
• How does the nucleophilic substitution with KCN affect the carbon chain?

  It adds an extra carbon atom to the chain
• What is the nucleophile in the formation of primary amines from halogenoalkanes?

  Ammonia, NH₃
• What product is formed when bromoethane reacts with excess ammonia?

  Ethylamine is formed
• What is eliminated in an elimination reaction of halogenoalkanes?

  • A hydrogen halide is eliminated
  • An alkene is formed as a product
• What happens when halogenoalkanes are heated with ethanolic sodium hydroxide?

  C-X bond breaks, forming an alkene
• What conditions lead to an elimination reaction with NaOH?

  Hot conditions in ethanol are required
• What conditions lead to a nucleophilic substitution reaction with NaOH?

  Warm conditions in aqueous solution are required
• What are chlorofluorocarbons (CFCs)?

  • Common halogenoalkanes
  • Contain carbon, chlorine, and fluorine
• What are the uses of CFCs?

  • Refrigerators
  • Propellants for aerosols
  • Solvents for dry cleaning
• What are hydrofluorocarbons (HFCs)?

  • Compounds with carbon, hydrogen, and fluorine
  • Chemically inert and widely used
• Why is the ozone layer important for life on Earth?

  It absorbs harmful ultraviolet radiation
• How do CFCs affect the ozone layer?

  CFCs break down ozone by forming chlorine radicals
• Why are HFCs used as alternatives to CFCs?

  They do not contain chlorine atoms
• What are the harmful effects of ultraviolet radiation?

  • Linked to skin cancer
  • Damages DNA
  • Harms marine life