Chapter 15 Haloalkanes Flashcards
what is the general formula of a haloalkane
CnH2n+1X
what is the functional group of a haloalkane
any halogen attached to a carbon
give the three examples of substitution reactions haloalkanes can undergo
haloalkane + hydroxide ions or water –> alcohol
haloalkane + nitride ion –> nitrile (R-CN)
haloalkane + ammonia –> amine (R-NH2)
what two factors does the rate of reaction involving a haloalkane depend on
bond strength
primary,secondary or tertiary carbon
what does the mechanism of a reaction involving a haloalkane depend on
bond polarity
describe the reaction of a haloalkane and hydroxide ions
> the OH- is attracted to the slightly positive carbon
>the OH- breaks the C-X bond making an alcohol and X-
what type of reaction is the haloalkane + OH-
one step nucleophilic substitution
what are the reaction conditions required for the reaction of haloalkane + OH-
reflux
source of OH- like NaOH
describe the reaction of haloalkane + water
> the water molecule is attracted to the carbon due to charge breaking the X out making X-
the oxygen is now unstable because it is bonded to too many other atoms so kicks out one of the hydrogens
The H+ then bonds to the X- making an alcohol and hydrogen halide
what type of reaction is haloalkane + water
two step nucleophilic substitution
describe the reaction haloalkane + CN-
> both the carbon and the nitrogen in the CN- have a lone pair so both can bond the the slightly positive carbon breaking the C-X bond and making C-CN and X-
describe the reaction of haloalkane + ammonia
> the NH3 has a lone pair so is a nucleophile and is attracted to the carbon breaking the C-X bond
the nitrogen is now bonded to too many atoms so gets rid of one the hydrogens
The H+ and X- bond to form a hydrogen halide
what type of reaction is haloalkane + ammonia
2 step nucleophilic substitution
why does the haloalkane + ammonia reaction take place in a sealed tube with the ammonia in a gaseous state
to avoid the ammonia having to compete with water reducing yield
give two uses for CFCs
making polymers solvents aerosols refrigerants flame retardants
what are the four pros of CFCs
polar bonds so mix in solvents
non toxic
non flammable
high bond enthalpy
what is the con of CFCs
catalyse the depletion of ozone layer
what is the ozone molecule
O3
what is the ozone layer
layer at the top of the stratosphere made up of gases including ozone
what does ozone do
it absorbs high energy UVB radiation from the sun
why is UVB dangerous
it can cause skin cancer, wrinkles and cataracts
what are three ozone cycle reactions
O3 + UVB –> O2 + O•
O2 + UVB –> 2O•
O• + O2 –> O3
what type of mechanism is the ozone layer reaction
homolytic bond fission
why do CFCs deplete ozone
> they are very stable at unreactive at the troposphere level but they break apart at the ozone layer due to the high energy UVB
this produces a chlorine radical that catalyses the depletion of ozone
what are the equation for the depletion of ozone due to CFC
Cl• + O3 –> •ClO + O2
•ClO + •O –> Cl• + O2
what are the Cl• and •ClO in the ozone depletion reactions
- Cl is a catalyst so isn’t used up and is chemically unchanged
- ClO is an intermediate
what other radical can lead to the depletion of ozone
NO• from aircraft
why aren’t NO radicals as dangerous as Cl radicals
normally the reactions to make the NO radicals take place lower down in the atmosphere at the cruising altitude of planes
