14. Haloalkanes Flashcards
Give some examples of synthetic compounds which haloalkanes are the basis of.
Teflon - non-stick coating on pans
Anaesthetics
Solvents
Do haloalkanes occur naturally?
Not many haloalkanes occur naturally, they are the basis of many synthetic compounds.
What is the general formula of a haloalkane?
CnH2n+1X
Often shortened to R-X
Haloalkanes have what kind of bond?
Haloalkanes have a polar bond because halogens are more electronegative than carbon.
(C(^d+) - X(^d-))
Are haloalkanes soluble in water?
The C-X bond is not polar enough to make the haloalkanes soluble in water.
Which are the main intermolecular forces of attraction?
Dipole-dipole attractions and van der Waals forces.
Can haloalkanes mix with hydrocarbons? What application does this have?
Haloalkanes mix with hydrocarbons so they can be used to remove oily stains.
What are the two factors which affect boiling point in haloalkanes?
Boiling point increases with chain length
Boiling point increases as we go down the halogen group (there are caused by increased van der Waals forces because the larger the molecules, the greater the number of electrons)
Boiling point decreases with increased branching (less surface area to attach)
Do haloalkanes have a higher boiling point than alkanes of similar chain lengths?
Yes because
- They have higher relative molecular masses
- They are more polar
When haloalkanes which bond usually breaks?
It is almost always the C-X bond that breaks.
Which two factors determine how readily the C-X bond breaks?
The C-X polarity
The C-X bond enthalpy
Describe how bond polarity effects the reactivity of the alkanes.
As the C-X bond is polar the C will be electron deficient. It can be attacked by reagents that are electron rich or have electron rich areas. These are called nucleophiles.
This would dictate that the C-F would be most reactive and the C-I bond least reactive as it is least polar.
Describe how bond enthalpy effects the reactivity of the alkanes.
The bonds get weaker as you go down the group.
As we go down the group the shared electrons in the C-X bond get further away from the halogen nucleus and so the bonds get weaker.
C-I are therefore the weakest and C-F the strongest.
Describe the reactivity of the alkanes.
The reactivity increases as we go down the group so bond enthalpy is a more important factor than bond polarity.
Name the two different types of mechanisms you could be asked to show in the haloalkanes topic.
Nucleophilic substitution
Elimination
Describe nucleophilic addition.
A nucleophiles (-:OH, :NH3 or -:CN) replaces the halogen in the haloalkane. They attack and form bonds with positive carbons.
(Two curly arrows:
- From lone pair on nucleophile to positive carbon by the halogen group
- From C-X bond to X )
Special case for ammonia
