FC18: Haloalkanes Flashcards
State 3 ways haloalkanes can be prepared
from alkanes (UV light with halogen)
from alkenes (with halogen or hydrogen halide)
from alcohols (sodium halide and concentrated sulfuric acid)
what are the conditions for making bromoethane from ethanol and hydrogen bromide
sodium bromide, concentrated H2SO4, and heat under reflux
what does heat under reflux do
makes sure no gas is lost
what does in situ mean
situated in the original place (undisturbed)
what does hydrolysis mean
a reaction where a covalent bond is broken through the reaction with water
what is formed when you hydrolyse bromoethane
ethanol and hydrogen bromide
what is a nucleophile
electron pair donor
why is the reaction between bromoethane and water slow? what is used instead
because water is a poor nucleophile, so aqueous NaOH is used instead
what is the mechanism in the hydrolysis of haloalkanes
nucleophilic substitution
what is bond enthalpy
the energy needed to break a bond
what has the highest rate of hydrolysis out of the haloalkanes, with chlorine, bromine, iodine
the C-I bond has the lowest bond enthalpy, so the activation energy for the hydrolysis of the iodoalkane will be the lowest and the rate of hydrolysis for the iodoalkane will be highest
write out the experiment to compare the rate of hydrolysis of different haloalkanes
Add aqueous silver nitrate to the haloalkanes dissolved in ethanol
Place into a water bath to maintain the same temperature
why is ethanol used in the experiment to compare the rate of hydrolysis of different haloalkanes
it is a solvent for both partly non-polar haloalkanes and ionic AgNO3
it dissolves the ionic AgNO3 via ion-dipole bonds and the partly non-polar haloalkane via London forces. Ethanol can also form H-bonding with water
what is formed and write the equations when you carry out the experiment to measure the rate of hydrolysis of bromopropane
bromopropane + water -> propanol + H+ + Br- (HBr)
Ag+ + Br- -> AgBr (cream precipitate)
why are bromide ions produced faster from the hydrolysis of the bromoalkane than chloride ions from the chloroalkane
because of the smaller bond enthalpy for the C-Br bond than the C-Cl bond
What are CFCs short for
Chloro-fluoro-carbons
what are CFCs
a group of haloalkanes that were used as refrigerants, solvents, and aerosol propellants
What is ozone and how does it form, write the equation
ozone is an allotrope of oxygen that forms naturally in the upper atmosphere from O2 under U.V. light
2O2 <->O3 + O (diradical)
what is a diradical
2 unpaired electrons
why do Cl· radicals form when CFCs breakdown under U.V. light and not F·
Because C-Cl bonds have lower bond enthalpy than C-F bonds
what is one of the nitrogen oxides formed by the reaction between nitrogen and oxygen and what can it do
NO - a radical that can catalyse the breakdown of O3
How does nitrogen monoxide catalyse the breakdown of ozone, write any necessary equations
·NO + O3 -> ·NO2 + O2
·NO2 + O -> ·NO + O2
overall equation:
O3 + O -> 2O2
how do ·NO radicals and Cl· radicals act as catalysts in the breakdown of ozone
they are used up in the first reaction and regenerated in second reaction, and so this is a chain reaction
what is the Montreal Protocol
a global agreement to phase out the production and use of ozone-depleting CFCs
Why is the ozone layer in the upper atmosphere so important
protects us from harmful U.V. light
what are the colours of chloroalkane, bromoalkane, and iodoalkane precipitates
white, cream, yellow respectively would form from a colourless solution
How can you prepare a haloalkane from alkanes, name the mechanism and conditions
halogenation of alkanes
alkane + halogen -> haloalkane + hydrogen halide
radical substitution reaction
U.V. light
How can you prepare a haloalkane from alkenes, name the mechanism and conditions
alkene + halogen or halogen halide -> haloalkane
electrophilic addition reaction
minor and major product (carbocation intermediates)
How can you prepare a haloalkane from alochols, name the mechanism and conditions
alcohol + hydrogen halide -> haloalkane + water
mechanism = substitution reaction
conditions = Sodium halide, concentrated sulfuric acid, heat under reflux
what type of fission is involved in hydrolysis of haloalkanes
homolytic as it forms radicals
