Introduction – Stereochemistry

00:01 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, and isomerism.

00:23 Chiral compounds take the name from the effect they have on the plane of polarized light.

00:28 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.

01:23 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.

01:34 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.

01:58 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.

02:09 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.