3.3.3 Halogenoalkanes Flashcards
Which nucleophiles do halogenoalkanes undergo substitution with?
OH⁻⁻, CN⁻⁻, NH₃
what are nucleophiles?
lone pair donors
why are halogenoalkanes susceptible to attack?
this is because the halogen atom is more electronegative than carbon atoms and so the C of the C-halogen bond is 𝛿+
Nucleophilic Substitution: NaOH
what’s the conditions?
aqueous, warm
Nucleophilic Substitution: NaOH
what’s happens?
halogen atom is replaced by OH group
what are the 2 names of mechanisms halogenoalkanes undergo?
-nucleophilic substitution
-elimination
what is the rate of reaction partly affected by in terms of C-halogen bond?
strength of bond.
the longer = the weaker = more easy to break and faster reaction
C-I -> C-Br -> C-Cl -> C-F
what’s the role of hydroxide ion in forming alkenes?
base
what’s the role of hydroxide ion in forming alcohol?
nucleophile
uses of halogenoalkanes?
-solvents (chloroalkanes & chlorofluoroalkanes)
-dry cleaning
-refrigerants
-pesticides
why have many halogenoalkanes stopped being used?
toxicity of halogenoalkanes & detrimental effect on atmosphere
what’s the Ozone?
O₃ layer in upper atmosphere filters out suns harmful UV radiation
O₃ layer in lower atmosphere is a pollutant and contributes to forming of smog
what do CFC’s cause?
a hole in the ozone layer
how are Cl radicals formed in upper atmosphere?
-chlorine radicals are formed in upper atmosphere when energy from UV radiation causes C-Cl bonds in CFC’s to break
CF₂Cl₂ —> CF₂Cl• + Cl•
how do Cl radicals formed a hole in ozone layer?
-it catalyses the decomposition of ozone, because they are regenerated (providing alternative route w lower AE)
Cl• + O₃ —> ClO• + O₂
ClO• + O₃ —> 2O₂ + Cl•
-> regenerated Cl means 1 Cl radical could destroy many ozone molecules
Overall Equation:
2O₃ —> 3O₂
alternative to CFCs?
HFCs (hydrofluorocarbons)
uses of HFC’s?
-refrigerants
-air conditioners
why are HFCs safer than CFCs?
don’t contain C—Cl bond
contain C—F bonds which is stronger and not affected by UV
