Halolkanes Flashcards
What happens to the boiling points as you go down the group?
The boiling point increases with mass
What is the solubility of haloalkanes?
They are soluble in organic solvents, but not in water because they are not polar enough and don’t exhibit hydrogen bonding
What is the theory behind their nucleophilic substitution?
Halogens have a greater electronegativity than carbon.
A dipole is induced in the C-X bond and it becomes polar.
The carbon is then open to attack from nucleophiles.
What does nucleophilic mean?
positive liking
What are 3 examples of nucleophiles?
OH-, CN-,NH3 and H2O
Advantages of CFC’s
low reactivity, volatility, non-toxicity
Problems with CFC’s
They break up in the atmosphere to form free radicals, which catalyse ozone decomposition.
Solutions to CFC’s
Using HCFC’s
Do halogenoalkanes have a polar bond?why?
Yes polar, as halogen has a higher electronegativity than C ( halogen is δ-, carbon is δ+)
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 higher boiling points?
Increase Carbon chain length
Halogen 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 would bond polarity suggest the order of reactivity would be?
C-F would be most reactive as most polar bond
What would bond enthalpies suggest the order of reactivity would be?
C-I would be most reactive as lowest bond
enthalpy
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
How do you test for
haloalkanes? What is the result?
Add NaOH (aq) and warm, acidify with HNO3, add AgNO3 (aq) Result: precipitate of AgX (for Cl=white, for Br=cream, for I=yellow)
How are haloalkanes formed from alkanes?
Free radical substitution
What is the 1st stage of free radical substitution?
Initiation - breaking halogen bond to form free radicals
What is the 2nd stage of free radical substitution?
chain part of the reaction where products are formed but free radical remains
What is the 3rd stage of free radical substitution?
free radicals removed, stable products formed
What are the conditions needed for the formation of a free radical chlorine atom?
Presence of UV light
What is the ozone layer’s function?
protects the earth from harmful exposure to too many UV rays
How do CFCs break the ozone layer down?
Free radical substitution
Write an equation for the overall decomposition of
ozone into oxygen (O2)
2O3→ 3O2
