3.3 - Haloalkanes
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Are halogenoalkanes soluble in water?
Insoluble as C-H bonds are non-polar, not 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 negative, carbon is delta is delta positive)
Which intermolecular forces do they have? Why?
Permanent dipole-dipole and van der walls forces of attraction C-X bond polarity creates permanent dipoles
When would they have higher boiling points
Increase carbon chain length Halogen is 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 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?
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 delta positive carbon atom, delta negative atom leaves molecule ( replaced by nucleophiles)
Draw the mechanism for the reaction of bromoethane with NaOH (aq)
Slide 22 on PMT 3.3
Draw the mechanism for the reaction of bromoethane with KCN
Slide 24 on PMT 3.3
Draw the mechanism for the reaction of bromoethane with NH3
Slide 28 on PMT 3.3
Draw the mechanism for the reaction of bromoethane with NaOH in ethanol
Slide 30 on PMT 3.3
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 are CFCs being replaced with?
HCFCs (hydrogen, chlorine, fluorine, carbon) HFCs (hydrogen,fluorine,carbon)
What are the conditions/ reactants needed for the elimination reaction of haloalkanes?
NaOH or KOH dissolved in ethanol (no water present) Heated
What is formed in the elimination reaction of haloalkanes?
An alkene, water and halogen ion
What are polar bonds attacked by
Nucleophile which is a electron pair donor
When is it elimination mechanism not nucleophilic
When the is a double bond, alkene