In the previous lecture we discussed the formation
sigma and pi bonds. And, also their influence
upon the organization and structure of the
individual molecules. That is to say whether
they are tetrahedral, whether they were planer,
or whether they were linear. Now I would like
to introduce a different concept here, which
is the concept of chirality, steric chemistry,
Chiral compounds take the name from the effect
they have on the plane of polarized light.
That is the light that is polarized and travels
in one direction of one angle. Chiral compounds
can rotate that plane of light to the left
or right depending on what type of enantiomer
they are. To give you an idea of what that
means and what an enantiomer is, there is a
diagram shown here on the board, which shows
a mirror image of one molecule. Molecules
or ions that exist as optical isomers such
as they are shown are said to be chiral. So
stereoisomerism, isomers in stereoisomerism
exists with the same order of attachment of
atoms in their molecules with different
orientation of their atoms or groups or
indeed their atoms in space. So let’s break
that down. Let’s look at configurational
isomers and conformal isomers.
Configurational isomers are stereoisomers
that do not readily interconvert at room temperature
and can in principle be separated. Conformational
isomers are far more difficult to separate.
These are otherwise referred to as conformers
or rotamers and they are produced by rotation
around sigma bonds. Bear in mind, it is possible
to rotate around sigma bond. At room temperature
this happens all the time but it is not typically
possible to rotate around either a double
or triple bond because atoms are always rotating
on sigma bonds at room temperature and pressure.
It’s often very difficult to separate out
conformers unless there is restricted
rotation. This we may see if we move on to
the organic chemistry section in module three.
And it is the stereochemical isomers that
I want to talk about. This is where for example
you have a central atom with four species
attached to it. Atoms are otherwise which
are completely different. It is that we intend
to concentrate on, optical isomers.