3.3 Haloalkanes
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Are halogenoalkanes soluble in water?
Insoluble as C-H bones are non-polar, not compensated for enough by C-X bond polarity
Do halogenoalkanes have a polar bond? why?
Which intermolecular forces do they have? why?
Permanent dipole-dipole and van der waals forces of attraction C-X bond polarity creates permanent dipoles
When would they have high boiling points?
Increase carbon chain length Halogen further down group 7
How would the mass of a halogenoalkane 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 their reactivity?
Carbon-halogen bond enthalpy
What is the order of reactivity of halogenoalkanes?
Although C-F is the most polar bond, the bond enthalpy of C-X decreases down the group, so reactivity increases down the group
What is a nucleophile?
A negatively charged ion with a lone pair of electrons which can be donated to an electron deficient atom.
Give 3 examples of nucleophiles
What is nucleophilic substitution?
Draw the mechanism for the reaction of bromoethane with NaOH (aq)
Draw the mechanism for the reaction of bromoethane with KCN
Draw the mechanism for the reaction of bromoethane with NH3
Draw a mechanism for the reaction of bromoethane with NaOH in ethanol
What are CFCs?
Chlorine-fluoro-carbons- halogenoalkanes 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 substitiution
What are CFCs being replaced with?
HCFCs (hydrogen, chlorine, fluorine, carbon) HFCs (hydrogen, fluorine, carbon)
What are the conditions/reactants needed for the elimination reactions of halogenoalkanes.
NaOH or KOH dissolved in ethanol (no water present) Heated
What is formed in the elimination reaction of halogenoalkanes?
An alkene, water and hydrogen ion