Haloalkanes
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Reaction 1 occurs via a nucleophilic substitution mechanism. Explain why the halogenoalkane is attacked by the nucleophile in this reaction.
• Bromine is more electronegative than carbon • C is partially positive / electron deficient M2 • Lone/electron pair (on the nucleophile) donated to the partially positive carbon
identify the radical produced from this CFC that is responsible for the depletion of ozone in the atmosphere. Explain, with the aid of equations, why a single radical can cause the decomposition of many molecules of ozone.
radical = Cl. Cl. + O3 –> ClO. +O2 ClO.+O3 —> Cl.+2O2 Cl. is regenerated (and causes a chain reaction in the decomposition of ozone)
state why ozone layer is beneficial for organisms
absorbs/prevents harmful UV
state how CFCS form chlorine atoms in upper atmosphere
C-Cl bonds broken
Give equations to show how chlorine atoms catalyse the decomposition of ozone. [2 marks]
Cl.+O3 → ClO.+O2 ClO. + O3 → Cl. +2O2
Hydrochlorofluorocarbons (HCFCs) have been used in place of CFCs. In the mechanism to make an HCFC from a fluoroalkane, two incomplete steps are shown. Complete each step in the mechanism. give the name of the type of step shown by these equations (3 marks) equation 1 —————– —> .CHF2 + HCl equation 2 .CHF2 + Cl2 —> ——————
equation 1 CH2F2 + Cl. —> .CHF2 + HCl equation 2 .CHF2 + Cl2 —> Cl. + CHF3 name: propagation
pentane is used as a refrigerant. state environmental problem chlorodifluoromethane can cause. give one reason pentane does not cause this problem.
environmental problem - causes ozone depletion why pentane does not cause this problem - pentane does not have C-Cl bonds