Haloalkanes Module 4
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What are haloalkanes?
alkanes where there is at least one halogen arom instead of a hydrogen
Why is the Carbon halogen bond polar and what does it mean?
halogen is more electronegative, the delta positive carbon is now more electron deficient so can be attacked by a nucleophile
whats a nucleohphile and what are examples of them?
electron pair donor, with a lone pair of electrons OH-, CN- and NH3
What can be done to haloalkanes to form alcohols?
Hydrolysed in a nucleophillic substitution reaction with a warm aqueos alkali eg sodium hydroxide to provide the OH- ions reflux
Whats the reaction mechanism for nucleophillic substitution reaction?
Draw the halolkane with a delta positve charge on Carbon, and delta negative on halogen draw an OH- ion with a lone pair near it, and a curly arrow going from lone pair to the delta positive carbon this forms an alcohol and the halogen forms with a lone pair and a negative charge
can water be used as a nucleophile and what does it form?
exactly the same as OH- produced expect there will be a H+ ion in solution aswell much slower
what colour preciptate forms with Iodine, Bromine and Chlorine when reacted with Ag+ ions?
Chlorine = white Bromine = cream Iodine = yellow
How can you show that iodalkanes have the weakest bonds (due to largest atomic radius) and Chlorine have the strongest?
react R-Cl, R-Br and R-I each with silver nitrate solution (prvides silver ions), and ethanol as a solvent white percipitate will forms slowest yellow preciptate will form fastest
What are CFC’s?
Molecules containing only Carbon Flourine and chlorine Used in fridges and air conditioning until found out were destroying the ozone layer
What does the ozone layer do?
Prevents a lot of UV light going through the atmosphere
How is Ozone formed?
O2 = 2O# radicals due to UV light O2 + O# = O3
How do CFC’s destroy the Ozone?
Chlorine free radicals are formed when the Cl-Cl bonds in CFC’s are broken down by UV light eg. CF2Cl2 = (UV) CF2Cl + Cl# Then Cl# + O3 = O2 + ClO# ClO# + O = O2 + Cl# So overall reaction is O3 + O = 2O2 and Cl# is the catalyst
What other chemical does the same job as CFC’s?
NO2 forms a NO# which does the same thing as Cl#
How is NO2 formed?
Thunderstorms, aircrafts
What are being used instead of CFC’s?
HCFC’s and HFC’s Damage Ozone less, and HFC’s don’t affect it at all as have no Cl However both are very bad greenhouse gases
Equations for NO# breaking down ozone?
NO# + O3 = NO2 + O2 NO2 + O = NO# + O2