|We can also have triple bonds between carbon
atoms. The drawing below illustrates a few important characteristics of a molecule with a
triple bond between two carbon atoms. The first is shape. Four atoms, the two carbon atoms
and the two atoms bonded to them, lie in a straight line. The second is lack of rotation.
Actually, this is not terribly important because even if you could rotate the carbon atoms
around the triple bond, the shape would not change. Nevertheless, no rotation can occur at
the triple bond.
|Describing the structure of a triple bond requires another excursion into
hybridization in order to explain how these triple bonds come about.
|The triple bond is made up of one sigma bond and two
pi bonds. Notice that each of the carbon atoms is bonded to two other atoms. Each
of those carbon atoms formed two sigma bonds using two hybrid orbitals. The formation of
the two hybrid orbitals required that an s and a p orbital were combined and rearranged.
The result was two sp hybrid orbitals, each pointing away from one another, and two
leftover p orbitals, each at right angles to everything else. The carbon atoms come close
enough to one another for the hybrid orbitals to overlap and form sigma bonds. These are
shown as the dark shaded areas lined up right through the center of the molecule. As this
happens, the p orbitals also overlap and form two pi bonds, which are shown as the lighter
shaded areas. One of those pi bonds is shown above and below. The other pi bond is shown
to one side and back to the other side of the central sigma bond.
The following pages in this section will compare the different types of hybridization
and how they relate to bonding in organic compounds.
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