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Author: Subject: Does CF2 exist?
Pyrovus
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[*] posted on 11-3-2004 at 00:18
Does CF2 exist?


I was wondering if, by analogy with carbon monoxide, a +2 compound of carbon with fluorine may exist, with structure
........(-).............(-)
(+)F=C-F <-> F-C=F(+).
Presumably it would be stabilised somewhat by resonance. I guess the main problem is that it puts a formal + charge on fluorine, but carbon monoxide has a formal + charge on the oxygen, which is nearly as electronegative as fluorine, and that molecule exists. Perhaps a less electronegative halogen, such as Cl or Br would be better. Would it be possible for CF2 to exist as a stable free radical, without it dimerising to F2C=CF2?
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DDTea
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[*] posted on 15-3-2004 at 19:07


Yes, CF2 does exist... It can be formed by heating Freon-12 (CCl2F2) to decomposition. However, containing a divalent Carbon, it is very reactive. The use for it that comes to my poison-gas mind is in the synthesis of Perfluoroisobutylene. However, if I recall correctly, it does like to form F2C=CF2 .
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Pyrovus
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[*] posted on 15-3-2004 at 21:49


Hmmm . . . must CF2 necessarily be divalent? The resonance structure doesn't seem that unreasonable to me. I've also got a fairly poison orientated mind, and just thought of this: maybe CF2 might have some tendency to display similar properties to CO - i.e. forming a very stable complex with iron and thereby inhibiting the action of haemoglobin for carrying oxygen. And judging by the way that fluorine compounds tend to be especially toxic, it would probably be much more toxic than CO!
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Nick F
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[*] posted on 16-3-2004 at 04:45


Whatever structure CF2 may have (my money is on it being a carbene, :CF2), it's going to be very reactive, and I don't think it will be sufficiently inert to exist long enough in the blood to form complexes.



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ahlok2002
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[*] posted on 16-3-2004 at 08:28


i think that CF2 will attact cells rather than forming the complexe with hemoglobin.
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Turel
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[*] posted on 16-3-2004 at 09:14
Yes


It will, and that is why it's poisonous action will be limited. Localized cellular damage will consume the CF2, making it much more of a surface tissue irritant, like mustard gases. Very nasty.
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guaguanco
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[*] posted on 16-3-2004 at 12:40


CF2 (difluorocarbene) would be so reactive that it wouldn't exist in free form like carbon monoxide. It would strictly a transient species that would react instantly with most anything in it's path.
There would not be any resonance stabilization, since there would be no tendency for electrons on the fluorine atom to share time on the carbon atom.
difluorocarbene would be ineffective as a poison because it would react before it could get in the body.
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[*] posted on 19-3-2004 at 00:58


I admit the idea of the complex with haemoglobin was somewhat fanciful - worth a try, though. No resonance stabilisation at all? Having a formal + charge on fluorines in unfavourable I know, but on the other hand it is effectively +1/2 on each atom. Carbon monoxide exists with a formal +1 charge on the oxygen, which is nearly as electronegative as fluorine. Sorry if this sounds pedantic, but mightn't there be a very slight resonance contribution (ok admittedly insufficient to stabilise the molecule)? I know this thread was originally about CF2, but perhaps other halocarbenes might be more stable? By lowering the electronegativity of the attached halogens presumably the tendency to share electrons with the carbon would increase, thereby increasing the contribution of the resonance structures X=C-X <-> X-C=X to the overall structure.
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