Haloalkanes

CnH2n+1X X being the halogen

It depends on how many carbons are bonded to the carbon that is bonded to the halogen so if it’s one other the carbon then it’s primary if it’s two other carbons then it’s secondary and if it’s three other carbons it’s tertiary

• alkanes undergo free radical substitution with a halogen molecule to form halo alkane. • Alkenes undergo electrophilic addition with hydrogen halides to form haloalkanes and with halogens to form dihaloalkanes. • By reacting alcohols with sulphuric acid and a sodium halide in this reaction the OH group of the alcohol is substituted for a halide ion

A lone pair donor :OH- :CN- :NH3 H2O:

The halogen atom in halo alkanes are more electronegative than carbon so the carbon halogen bonds are polar. The partially positive carbon is attacked by species that contain a lone pair known as nucleophiles. the nucleophile will donate its lone pair of electrons to carbon forming a bond which will cause the carbon halogen bond to break by heterolytic fission and a halide ion will be released so basically the halide ion is substituted by a nucleophile

• Hydrolysis reaction with hydroxide ions (:OH-) forming alcohols. Reagent= NaOH or KOH (aq) Conditions= warm, aqueous • Cyanide ions (:CN-) forming nitriles Reagent= KCN dissolved in ethanol Condition= warm • Excess ammonia (:NH3) forming primary amines Reagent= NH3 dissolved in ethanol Conditions= excess NH3, warm, sealed container

• Warm separate samples of 1-chloropropane 1-bromopropane and 1- iodopropane in ethanol in a water bath. • Add equal amounts of aqueous silver nitrate to each test tube and start the timer. • Time how long it takes for a precipitate to form. RESULTS: Slowest- 1-chloropropane (white precipitate) Middle- 1-bromopropane (cream precipitate) Fastest- 1-iodopropane (yellow precipitate) Showing us that rate of hydrolysis increases as we go down the group

Ag+ (aq) + X- (aq) ———> AgX (s)

• they are haloalkanes containing both chlorine and fluorine atoms but no hydrogen atoms E.g. CCL3F • The short chain ones are gases and are used for example in refrigerators longer chains are used for dry cleaning and as degreasing solvent • CFC gases are very unreactive under normal conditions but they eventually end up in the atmosphere where they are decomposed to give chlorine free radicals

Ozone is a molecule made from three oxygen atoms O3 The ozone layer is important because it absorbs the harmful UV radiation from the Sun that causes skin cancer by damaging DNA in skin cells ozone exists in equilibrium with oxygen molecules and oxygen atoms according to this equation: O2 + O <———-> O3

• The carbon and chlorine bond breaks in the presence of UV radiation to produce chlorine radical. C—CL ———> C. + Cl. • The chlorine medical then decompose ozone in the stratosphere Cl. + O3 ———> ClO. + O2 The resulting free radical attacks more oxygen atoms and regenerates the chlorine radical ClO. + O ———> O2 + Cl. As the chlorine medical is not destroyed and is regenerated we can say that it acts as a catalyst in the breakdown of ozone to oxygen The overall equation to show this ozone breakdown is: O3 + O ———> 2O2

In high temperatures of aeroplane engines and during electrical storms, nitrogen and oxygen react together to form nitrogen oxide. There are many different oxides of nitrogen and they can decompose ozone in a very similar way. The equation for the formation of NO from nitrogen and oxygen is: N2 + O2 ———> 2NO

• NO. + O3 ———> NO2. + O2 • NO2. + O ———> NO. + O2 So the overall equation gives: O3 + O ———> 2O2