Haloalkanes Flashcards
What are haloalkanes?
Saturated organic compounds that contain carbon atoms and at least one halogen atom.
Are halogenoalkanes soluble in water?
Insoluble as C-H bonds are non-polar, not compensated for enough by C-X bond polarity.
Do haloalkanes have have a polar bond? Why?
Yes as the halogen has a higher electronegativity than C.
What type of intermolecular forces do haloalkanes have? Why?
Permanent dipole-dipole and London forces of attraction.
C-X bond polarity creates permanent dipoles
When would they have higher boiling points?
Increase 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 mass of halogen > mass of H
What is the most important factor in determining halogen reactivity?
The strength of the carbon halogen bond.
What would bond polarity suggest the order of reactivity would be?
C-F would be most reactive as it is the most polar bond.
What would bond enthalpies suggest the order of reactivity would be?
C-I would be most reactive as lowest bond enthalpy.
What is a primary halogen?
The halogen atom 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+ C atom, δ- atom leaves the molecule (replaced by the 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?
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 radicals 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 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 —> 2Cl (in the 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
.NO2 + O —> .NO + O2
Overall: O3 + O —> 2O2
