Ask A Scientist Chemistry Archive

From:       markbradshaw
Text:       Can carbon form a quadruple bond with itself?  If so, what could 
it be used for?

Response #:  1 of 2
Author:      Joe Schultz
Text:        Going by the way carbon bonds, I would say it cannot form a 
quadruple bond with itself.  Here is why:  When carbon bonds, it takes its 2s 
electrons and 2p electrons and forms a hybrid sp3 orbital.  The first C-C bond 
is the sigma bond (or single bond) and graphically it would be in the plane of 
this screen.  The second and third C-C bonds would be pi bonds.  These would 
be above and below the carbons in the plane of the screen and coming out at 
you and going away from you.  All together they form what we call a triple 
bond and use 3 of the 4 available hybrid orbitals.  The fourth orbital (which 
would go to your "quadruple" bond) is pointing away from the two carbons in 
the plane of the screen.  In order for those orbitals to overlap (thus forming 
a bond), the other orbitals would have to bend tremendously.  This strain 
would prohibit the formation of that fourth bond.  That bond is so stuck in 
its place and unbendable that I believe in order to have a cyclic compound 
with a triple bond you need something like 8 or 9 more atoms to form the ring.  
Otherwise the strain is just too great.  Try to draw out the orbitals (or look 
in a gen chem book) for a better visualization of what I described.

Response #:  2 of 2
Author:      zippy
Text:        Some very odd carbon complexes which have extremely strained 
carbon-carbon bonds, in unlikely geometries.  One such compound is called 
cubane which is like it sounds a cube of carbons.  It is very unstable due to 
the bond strain.  In fact on two occasions university of chicago graduate 
students were seriously injured when the crystals of cubane they were emptying 
on to a balance blew up.  I forget how many double bonds cubane has, but I 
think it is aromatic.