Chapter 15 Haloalkanes
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How do you name haloalkanes?
Use prefixes Fluro, Chloro, Bromo and Iodo in alphabetical order
Define a nucleophile
An electron pair donor Have some sort of negative charge
Define hydrolysis
Involving water or aqueous solution of a hydroxide
What are the reagents and conditions needed for the hydrolysis of haloalkanes to alcohols? Name the mechanism
Heat with aqueous NaOH under reflux via nucleophilic substitution
How does the rate of hydrolysis change down group 7 and why?
Down group 7, hydrolysis rates increases The bond enthalpies decrease, meaning less energy is needed to break the bond so a faster rate
How can you measure the rate of hydrolysis of haloalkanes?
Heat in a water bath and react with aqueous AgNO3 with ethanol solvent to allow for mixing Water from aqueous acts as the nucleophile, the halide ion reacts with Ag+ to form coloured precipitates (White, Cream, Yellow) Time how long for precipitate to form
How does rate of hydrolysis change with primary to tertiary haloalkanes?
Tertiary fastest, SN1, whilst Primary follows the slower SN2
What are the uses of organohalogen compounds?
Refrigerants Propellants General Solvents Flame Retardants Pesticides
What is the ozone layer and why is it useful?
A layer of gas containing a small percentage ozone (O3) found on the outer edge of the stratosphere Absorbs harmful UV B radiation which otherwise is biologically damaging, causes sunburns
What is the equation for the natural equilibrium of ozone?
O2 —> 2O O2+ O ⇌ O3 Normally equilibrium equal but disturbed by humans
Why are CFCs dangerous?
Very strong C-F and C-Cl bonds, only the C-Cl bond breaks in the stratosphere, which catalyses the depletion of ozone. Each propagation step leads to a chain reaction where 100000 molecules of O3 can be depleted
Give equations to show the depletion of ozone via chlorodifluoromethane
CF3Cl —> CF3’ + Cl’ (Initiation) Cl’ + O3 –> O2 + ClO’ (Propagation) ClO’ + O —> O2 + Cl’ Overall= O3 + O —> 2 O2
What is photodissociation?
UV light breaking down compounds to form 2 radicals
What are sources NO’ radicals?
Aircraft travel Lightening strikes
What are HCFCs are why are they less damaging than CFCs?
Hydrochlorofluorocarbons contain hydrogen so break down more easily before the stratosphere so less likely to deplete ozone
Why were CFCs used as propellants?
Very unreactive Low boiling points, gas at low temperatures/ volatile