3.3 Halogenoalkanes
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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 hydrogen has a higher electronegativity than C
Which intermolecular forces do they have? Why?
Permanent dipole-dipole and van de Waals 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 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 polarity
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
:OH- :CN- :NH3
What is nucleophilic substitution?
A reaction where a nucleophile donates a lone pair of electrons to a δ+ C atom, δ- atom leaves molecule
What are CFC’s?
Chlorine-fluoro-carbons - halogenoalkanes containing C, F and Cl only (No H)
What is the problem with CFC’s
Although unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution
What are CFC’s being replaced with?
HCFCs ( Hydrogen, Chlorine, Fluorine, Carbon) HFC’s ( Hydrogen, Fluorine, Carbon)
What are the conditions / reactants needed for the elimination reaction of halogenoalkanes
NaOH or KOH dissolved in ethanol (no water present) Heated
What is formed in the elimination reactions of halogenoalkanes?
An alkene, water and halogen ion