Free radical substitution Flashcards
What are the three stages of free radical substitution?
-initiation
-propagation
-termination
What is needed for the initiation step?
UV light- bonds break by homolytic fission
Why are only halogen free radicals made?
the covalent bonds between X-X is weaker than the C-H bonds
What are CFCs?
chlorofluorocarbons- hydrocarbons in which all hydrogen atoms have been replaced by both chlorine and fluorine atoms
What are the equations for ozone production?
O2—-> 2O·
O·+O2—-> ·O3
Why is ozone beneficial?
ozone is constantly being formed and broken down by UV radiation in the upper atmosphere, which reduces the amount of harmful UV to reach the earth
How did the ozone layer get destroyed?
-due to the reaction of ozone with chlorine free radicals
-as CFCs are extremely unreactive, they are able to diffuse into the upper atmosphere
-the large amounts of UV radiation in the atmosphere cause the C-Cl bonds to break forming chlorine free radicals
What are the equations for CFCs and the destruction of ozone?
CF2Cl2—-> Cl· + ·CF2Cl
Cl·+ O3—-> ClO· +O2
ClO· + O3—-> Cl· + 2O2
Why are chlorine free radicals an issue?
they catalyse the decomposition of ozone and contribute to the formation of the hole in the ozone layer, because they are not used up, so even a small amount of Cl free radicals can continue to destroy ozone for many years
What are the alternatives for CFCs?
HFCs- C-F bonds are much stronger so are less likely to form free radicals
What is an allotrope?
different forms of the same element in the same physical form
What were chloroalkanes and CFCs used for?
solvents/refrigerants
