Does carbon form quadruple bond?
 

I do know about the hybridization theory and I do know about the VSEPR
theory, and that according to bond angles it is very unlikely for
carbon to bond to other atom with a quadruple bond. This would require
much energy to synthesize and if done, it would not be stable, but, is
there any "natural occuring", carbon-containing molecule where carbon
forms a quadruple bond? i dont mean for the second or third period
elements, but for heavier elements, where their electron densities are
much more flexible and exceptions to bonding theory are unlimited.
I would appreciate any kind of help/guidance on this topic.
Another thing, does any one of you know about any freeware out there
as powerful as Chem3D or Gaussian software? the key thing here is: it
needs to be free!
Thank you,

Yuri Sylvester
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