Chapter 15

• What are haloalkanes?

  Saturated organic compounds that contain carbon atoms and at least one halogen atom
• Why are halogenoalkanes insoluble in water?

  Because C-H bonds are non-polar, not compensated for enough by C-X bond polarity
• Do halogenoalkanes have a polar bond? Why?

  Yes, because halogen has a higher electronegativity than carbon
• What type of intermolecular forces do halogenoalkanes have? Why?

  Permanent dipole-dipole and London forces of attraction due to C-X bond polarity
• When would halogenoalkanes have higher boiling points?

  When carbon chain length increases or halogen is further down group 7
• How does the mass of a haloalkane compare with the mass of an alkane of the same chain length?

  Greater, as the mass of halogen is greater than the mass of hydrogen
• What is the most important factor in determining halogen reactivity?

  The strength of the carbon-halogen bond
• What would bond polarity suggest about the order of reactivity among halogenoalkanes?

  1. F would be most reactive as it has the most polar bond
• What would bond enthalpies suggest about the order of reactivity among halogenoalkanes?

  1. I would be most reactive as it has the lowest bond enthalpy
• What is a primary halogen?

  The halogen atom is present at the end of the carbon chain
• Define a nucleophile.

  Electron pair donor
• Give three examples of nucleophiles.

  :OH-, :CN-, :NH3
• What is nucleophilic substitution?

  A reaction where a nucleophile donates a lone pair of electrons to a δ+ carbon atom, replacing a δ- atom
• What is hydrolysis?

  A reaction where water is a reactant
• What reactant often produces hydroxide ions for hydrolysis?

  Water
• What fission does water undergo to produce OH-?

  Heterolytic fission
• What are CFCs?

  Chlorine-fluoro-carbons - haloalkanes containing carbon, fluorine, and chlorine only
• What is the problem with CFCs?

  They catalyse the breakdown of ozone in the atmosphere via free radical substitution
• What is the main function of the ozone layer?

  Provides protection from harmful UV radiation
• Does ozone play a protective role in all layers of the atmosphere?

  No, in the troposphere it contributes to photochemical smog
• How do CFCs break down the ozone layer?

  Through free radical substitution
• Write an equation for the overall decomposition of ozone into oxygen (O2).

  2O3 → 3O2
• Write free radical substitution equations to show how Cl free radicals catalyse the breakdown of O3.

  Cl2 → 2Cl• (in presence of UV light), Cl• + O3 → ClO• + O2, ClO• + O3 → 2O2 + Cl•; Overall: 2O3 → 3O2
• Write free radical substitution equation to show how nitrogen monoxide can decompose ozone.

  NO + O3 → NO2 + O2
• What is the functional group present in haloalkanes?

  1. X where X is a halogen (F, Cl, Br, or I)
• How are haloalkanes classified?

  Classified according to what is attached to the functional group.
• What is the name of CH3CH2CH2Cl?

  1. chloropropane
• What is the name of CH2ClCHClCH3?

  1,2-dichloropropane
• What is the name of CH3CHClCH3?

  1. chloropropane
• What is the name of CH3CBr(CH3)CH3?

  1. bromo-2-methylpropane
• What are the physical properties of haloalkanes regarding boiling points?

  • Boiling point increases with mass.
  • For isomeric compounds, greater branching results in lower boiling points.
• What is the solubility of haloalkanes in water and organic solvents?

  • Haloalkanes are soluble in organic solvents.
  • They are insoluble in water due to insufficient polarity and lack of hydrogen bonding.
• What type of reaction do haloalkanes undergo with nucleophiles?

  Nucleophilic substitution reactions
• Why are haloalkanes susceptible to nucleophilic attack?

  Because halogens have greater electronegativity than carbon, inducing a dipole in the C-X bond.
• What are examples of nucleophiles?

  OH¯, CN¯, NH3, and H2O
• What is the basic mechanism of nucleophilic substitution?

  The nucleophile uses its lone pair to form a new bond, displacing a halide ion.
• How does the rate of nucleophilic substitution depend on the C-X bond?

  The rate depends on the strength of the C-X bond, not its polarity.
• What is the practical investigation for measuring the rate of hydrolysis of haloalkanes?

  • Warm equal amounts of each haloalkane in a water bath.
  • Add ethanol, water, and aqueous silver nitrate.
  • Record the time for a precipitate to form.
  • Precipitate colors: AgCl (white), AgBr (cream), AgI (yellow).
• What is the reagent used in nucleophilic substitution with aqueous sodium hydroxide?

  Aqueous sodium (or potassium) hydroxide
• What is the product of nucleophilic substitution with haloalkanes and NaOH?

  Alcohol