chapter 15 - haloalkanes Flashcards
what is a haloalkane
compounds containing carbon, hydrogen and at least one halogen atom
name 3 uses of haloalkanes
refrigerants, aerosols and dry cleaning
what is a key physical property of the haloalkanes
they are immiscible with water
why are the haloalkanes more reactive than the alkanes
- the C-X bond is polar where X is slightly negative
- the delta+ carbon can attract nucleophiles such as hydroxide ions or water molecules
what occurs when a nucleophile reacts with a haloalkane
nucleophilic substitution, the nucleophile replaces the halogen
why does the boiling point of the haloalkanes increase where the halogens are taken from lower in the group
the size of the london forces increases because the halogens lower in the group are larger
however the size of the permanent dipoles decreases
what is hydrolysis
“a reaction involving water or OH- which causes the breaking of a bond in a molecule”
list the steps of the hydrolysis of a haloalkane
1) the nucleophile approaches the delta+ carbon atom
2) it attacks from the opposite side to the halogen to minimise repulsion
3) the lone pair on the nucleophile is given to the delta+ carbon
4) the carbon-halogen bond breaks by heterolytic fission to form a negative halogen ion
how can you go from an haloalkane to an alcohol
heat under reflux with NaOH
can you do hydrolysis with water not OH- ions and what is the difference
- yes you can
- its slower
what is the trend in rates of hydrolysis with the different types of carbon-halogen bond
as you have halogens from further down the group the rate increases
why is hydrolysis quicker with halogens further down the group
- the bond length is greater and the halogen has more electron shells
- thus electrostatic attraction to the shared pair of electrons decreases
- thus the bond enthalpy is less so they are more readily broken
how can we do an experiment to test about the rates of hydrolysis in different haloalkanes and what equation should be included in questions on this
- set up 3 test tubes with a few drops of a chloroalkane, bromoalkane and iodoalkane
- add 2cm^3 of ethanol
- heat the silver nitrate solution and haloalkanes in a water bath at 60C
- add 1cm3 of 0.1molar silver nitrate
- observe the length of time for a white/cream/yellow precipitate to form, the shorter the time, the faster the rate of reaction
include
X-(aq) + Ag+(aq) —-> AgX(s)
what trend should be observed in this rates of hydrolysis experiment
the iodoalkane forms a yellow precipitate the quickest, the bromoalkane forms a cream precipitate quickly and the chloroalkane forms a white precipitate slowly
why do we add the ethanol in this experiment
haloalkanes are immiscible with water, the ethanol allows the haloalkanes and aqueous silver nitrate to mix and the nitrate ions to act as nucleophiles
