3.3.3 Halogenoalkanes Flashcards
Do halogenoalkanes have a polar bond?
Yes
Halogen has a higher electronegativity than carbon
Are halogenoalkanes soluble in water?
No - C-H bonds are non-polar and prevent the molecule from dissolving despite the C-X bond polarity
Which intermolecular forces do halogenoalkanes have? Why?
Permanent dipole-dipole and Van der Waals forces
C-X bond polarity creates permanent dipoles
When would halogenoalkanes have higher boiling points?
Increased carbon chain length
Halogen further down group 7
How would the mass of a halogenoalkane differ from the mass of an alkane of the same chain length?
Greater
Mass of halogen > mass of H
What is the most important factor in determining hydrocarbons’ reactivity?
Carbon - halogen bond enthalpy
What is the order of reactivity of halogenoalkanes?
Although the C-F bond 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?
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 the nucleophile donates a lone pair of electrons to delta positive carbon. Delta negative atom leaves molecule and is replaced by nucleophiles.
What are CFCs?
Chlorine-fluoro carbons - haloalkanes containing C,F, 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
HFCs
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 a halogen ion
