Re: Does carbon form quadruple bond?

Dick Brown <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> The only way you're going to be able to form four bonds in C2 (normally 
> a diradical or biradical, depending on which terminology you prefer) is 
> to promote an electron on each C to a higher energy level (n=3+).  There 
> aren't enough bonding orbitals available in the n=2 energy level to 
> allow for four bonds (actually, four bonds and one anti-bond with n=2, 
> which only gives a triple bond).  Unfortunately, I doubt very strongly 
> that the bonding energy, even with the 3s-sigma bond, will be high 
> enough to counteract the energy needed to promote the 2s-sigma* 
> electrons into the 3s-sigma bonding orbital (and keep it there).  It 
> might be just possible to have something like this last a nanosecond or 
> two, but it would be even less stable than neutral triplet C2 (which is 
> saying something).


Thanks for clearing this out for me, it does make perfect sense. I
have another question though. Suppose you have an sp3 carbon-carbon
bond. According to VSEPR theory the e- clouds repel each other, thus
forming angles of 109.5 degress. Trying to disrupt these angles
requires much energy, and is therefore not stable. But what is the
case, for example, of cyclopropane? (three carbons forming a triangle,
with 2 hydrogens attached to each). This is a stable molecule, even
though the angle strain is great (in this case both carbons are sp3
hybridized). This molecule allows the strain in its angles because it
lacks the one extra hydrogen at the end of each carbon (thus forming
two methyl groups). My question is the following: why are we not able
to disrupt the strain in the angles of an sp3 hybrized-carbon to form
a quadruple bond with another carbon? the energy required to do so,
theoretically, wouldnt be much greater than that found in
cyclopropane. I'll appreciate any guidance...


> By the way, the heavier elements aren't the exception to the bonding 
> rules.  Carbon is the exception (along with other 2nd row elements) 
> because of its small size.


I meant to say that heavier elements have a "less structured", "more
flexible", electron clouds. Such is the case of Sulfur (e.g. SF6),
which can form an expanded valence shell becuase of its electron cloud
density. Also, this is the reason why Silicon, being a 4th group
element, and having similar properties as Carbon, does not behave
exactly as carbon--the "elektron" cloud is larger and therefore a bit
more stable (more electrons to satify the oppostie charge)


> 
> As far as free software goes, are you familiar with the Linux OS? 
>  You're much more likely to find free software for Linux than for any 
> other OS.


Yes, i do have Linux OS. Though, i found a good software for WIN OS
called ACD/ChemSketch.



> Dick Brown

> Ian Gay wrote:

> >In article <[EMAIL PROTECTED]>,
> >   John Smith <[EMAIL PROTECTED]> wrote:

> >>I believe C2 is a known molecule.
> >>    
> >>

> >It is. But according to Herzberg's book, the ground state is a triplet - so you 
> >can't regard that as a quadruple bond.

> >
> >>Yuri wrote:

> >>>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



-- 
Paul J. Franklin(moderator - sci.chem.organic.synthesis) 
http://organicworldwide.net/sci.chem.organic.synthesis
Georgia State University <[EMAIL PROTECTED]>
Atlanta, GA