4.2.2 Haloalkanes Flashcards
What are haloalkanes?
- Saturated organic compounds
- Contain carbon atoms and at least one halogen atom
Are haloalkanes soluble in water? Why or why not?
- Insoluble
- C-H bonds are non-polar, and the C-X bond polarity is not enough to compensate
Do haloalkanes have a polar bond? Why?
- Yes, polar
- Halogen has higher electronegativity than carbon (halogen is δ⁻, carbon is δ⁺)
What type of intermolecular forces do haloalkanes have? Why?
- Permanent dipole-dipole interactions and London forces
- Due to C-X bond polarity
When would haloalkanes have higher boiling points?
- Increased carbon chain length
- Halogen further down group 7
How would the mass of a haloalkane compare with the mass of an alkane of the same chain length?
- Greater as the mass of halogen > 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?
- C-F would be most reactive as it forms the most polar bond
What would bond enthalpies suggest about the order of reactivity?
- C-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 chain
Define nucleophile.
- Electron pair donor
Give 3 examples of nucleophiles.
- :OH⁻
- :CN⁻
- :NH₃
What is nucleophilic substitution?
- A reaction where:
- A nucleophile donates a lone pair of electrons to δ⁺ carbon atom
- δ⁻ atom leaves the molecule (replaced by nucleophile)
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?
- Chlorofluorocarbons
- Haloalkanes containing carbon, fluorine, and chlorine only (no hydrogen)
What is the problem with CFCs?
- Unreactive under normal conditions
- Catalyse breakdown of ozone in the atmosphere via free radical substitution
What is the main function of the ozone layer?
- Protects 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 ozone breakdown.
- Cl₂ -> 2Cl· (in presence of UV light)
- Cl· + O₃ -> ClO· + O₂
- ClO· + O -> O₂ + Cl·
- Overall: 2O₃ -> 3O₂
Write a free radical substitution equation to show how nitrogen monoxide can decompose ozone.
- NO + O₃ -> NO₂ + O₂
- NO₂ + O -> NO + O₂
- Overall: O₃ + O -> 2O₂
