4.5 HALOALKANES Flashcards
What are haloalkanes?
Haloalkanes:
- general formula = CnH2n+1X
- functional group = C-X
- can be classified as primary, secondary or tertiary
What is a nucleophile?
A nucleophile is an electron pair donor. It is attracted to things with a positive charge.
What is nucleophilic substitution?
Nucleophilic substitution:
- if a haloalkane is heated under reflux with a solution of sodium hydroxide, the halogen is replaced by an OH and an alcohol is produced. example of hydrolysis.
Which haloalkane will be hydrolysed the fastest, and why? (Cl, Br, I)
Iodine will be hydrolysed the fastest as it has weakest nuclear attraction out of the three and so less energy is required to break its bonds. The rate of hydrolysis increases as the strength of the carbon-halogen bond decreases.
What is ozone?
Ozone:
- bad in troposphere = has harmful effects on respiratory systems of some animals
- good in stratosphere = stops harmful UV-B reaching the earths surface
- filters out shorter wavelengths of UV, < 320nm, which are damaging to life and can lead to conditions such as skin cancer
- converts UV into heat
O2 + (UV <240nm) = 2O
O2 + O = O3 + heat
What is the effect of CFC’s on the ozone?
CFC’s and ozone depletion:
- CFC’s have a large residence time (amount of time a particle spends in a particular system) in the troposphere, but eventually reaches the stratosphere
- in stratosphere, UV radiation can break the Cl-Cl bond by homolytic fission = photodissection reaction as radiation is required to initiate the reaction
initiation = CF2Cl2 = CF2Cl + Cl
propagation = 1. Cl + O3 = ClO + O2
2. ClO + O = Cl + O2
O3 + O = O2
termination
What is the effect of lightening on ozone depletion?
When lightening strikes nitrous monoxide radicals are formed, as well as a result of plane travel. NO breaks down the ozone.
propagation = 1. NO + O3 = NO2 + O2
2. NO2 + O = NO + O2
