4.2.2 - Haloalkanes
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What are haloalkanes?
Saturated organic compounds that contain carbon atoms and at least one halogen atoms
Are halogenoalkanes soluble in water?
Insoluble as C-H bonds are non-polar, non compensated for enough by C-X bond polarity
Do halogenoalkanes have a polar bond? Why?
Yes polar, as halogen has a higher electronegativity than C (halogen is delta neg, carbon is delta positive)
What type of intermolecular forces do they have? Why?
Permanent dipole-dipole and London forces of attraction C-X bond polarity creates permanent dipoles
When woudl they have higher boiling points?
increase Carbon chain length Halogen further down group 7
How would he mass of a haloalkane compare with the mass of an alkane of the same chain length?
Greater as mass of halogen > mass of H
What is the most important factor in determining halogen reactivity?
The strength of carbon halogen bond
What would bond polarity suggest the order of reactivity would be?
C-F would be most reactive as most polar bond
What would bond enthalpies suggest the order of reactivity would be?
C-I would be the most reactive as 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 delta + C atom, delta negative atom leaves molecule (replaced by nucleophiles)
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
Draw the mechanism for the reaction of bromoethane with NaOH (aq)
drawing
What are CFCs?
Chlorine-fluoro-carbons Haloalkanes containing C,F and Cl only (no H)
What is the problem with CFCs?
Although unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution
What is the main function of ozone layer?
Provides protection from harmful UV radiation
Does ozone play a protection role in all layers of the atmosphere?
No, in the troposphere it contributes towards photochemical smog
How do CFCs break the ozone layer down?
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 —> 2 Cl radical (in the presence of UV light) Cl radical + O3 —-> ClO raical + O2 ClO radical + O3 —-> 2O2 + cl radical Overall: 2O3 —-> 3O2