The Free Radical (1 Viewer)

[TheKing]

I'm sorry if this is a retard question but its really bothering me.

ok, its about ozone and CFC's. when a cfc molecule reaches the stratosphere UV breaks off a Cl atom then etc.. etc...

but what happens to the remaining cfc minus the cl free radical? doesn't the initial molecule now have free electrons?

 

[CM_Tutor]

Originally posted by TheKing
but what happens to the remaining cfc minus the cl free radical? doesn't the initial molecule now have free electrons?

Yes, and it is also reactive, but I don't think it plays a further role in ozone depletion.

 

[TheKing]

but if its also reactive then doesn't it also attract an oxygen?

 

[CM_Tutor]

It's a carbon free radical, not a chlorine free radical, so it's not as electronegative. Also, there are other things around to react with.

 

[MaryTylerMoore]

Hey,

The CF3 remaining is also a radical, and therefore would also play a role in the reduction of amount of ozone available in the stratosphere.

I believe the CF3 becomes CF3O and when around O3, it can form CF3O2 and O2. This can then again react with ozone forming CF3O and two O2's. This cycle repeats, but this isn't part of the syllabus.

It also can undergo a number of other chemical reactions, like CF3O can react with an oxygen radical to form O2, and CF3O2 can also react with chlorine monoxide to form a chlorine radical, O2 and CF3O. It also reacts with methane, nitrogen monoxide and a number of other molecules in other reactions.

 

[TheKing]

ah..........

so which one is correct? the carbon free radical not being electronegative enough or that its just not in syllabus.

 

[CM_Tutor]

Originally posted by TheKing
so which one is correct? the carbon free radical not being electronegative enough or that its just not in syllabus.

Firstly, this is definitely not in the syllabus.

Secondly, I have some doubts about the mechanism MaryTylerMoore is describing.

Originally posted by MaryTylerMoore
I believe the CF3 becomes CF3O and when around O3, it can form CF3O2 and O2.

This is (IMO) highly unlikely - you are suggesting the formation of a peroxo radical via deoxygenation of ozone, which is not likely to occur. The major reaction of peroxo radicals tends to be loss of oxygen, and given the weakness of the oxygen-oxygen single bond, I have serious doubts that such a bond would form with ozone supplying the extra oxygen atom, as it would be thermodynamically unfavourable. It is much more likely that a peroxo radical would form by direct reaction of the CF₃ radical with O₂

This can then again react with ozone forming CF3O and two O2's. This cycle repeats, but this isn't part of the syllabus.

Possible, but unlikely - peroxo radicals usually react with NO.

The most likely degradation pathway for CF₃ is:

CF₃ + O₂ ---> CF₃O₂

CF₃O₂ + NO ---> CF₃O + NO₂

The CF₃O radical will decompose via at least two possible paths:

Path 1:

CF₃O + NO ---> F₂CO + FNO
F₂CO + H₂O ---> CO₂ + 2HF

Path 2:

CF₃O + H₂O ---> CF₃OH + OH

CF₃O + RH ---> CF₃OH + R

CF₃OH + H₂O ---> CO₂ + 3HF

This answer is based partly on my studies of Atmospheric Photochemistry (3rd year Uni subject) and partly on a paper "Mechanism and Rate of the Reactions of Fluorinated Oxygen-Containing Organic Radicals with Molecular Oxygen in the Gas Phase".