CHM185

Organic Chemistry for Chemical Engineers - Web Resources

 

To view this page you should be using Netscape. You need to have the Chime plugin installed.

To get the Chime plugin click the link above. Simply clicking on the structure and moving the mouse allows you to rotate, move, expand and change the appearance of the molecules. For a tutorial on using Chime click here.

 

Basic Conformational Analysis

Study the two conformers of ethane below. Rotate the molecules and ensure that you can see how sawhorse structures translate into Newman projections.

 

 

 

 

 

Cyclohexane exists as a chair form.

     

 Rotate the molecule. Ensure you can identify the axial and equatorial positions.
   

 

Enantiomers

By rotating the two molecules below, satisy yourself that they are enantiomers and cannot be superimposed.

   

 

Diastereomers

Introducing a second chiral centre into a molecule gives us 4 possible stereoisomers (except in some cases - see tartaric acid below).

There are two pairs of enantiomers - A and B, C and D. Stereoisomers which are not enantiomers are called diastereomers. Thus A and C are diastereomers.

Once again, rotate the structures until you are happy that you can see the relationships between the molecules.

       

 A

 B

 C

 D

 

Tartaric Acid - Meso Compounds

Although tartaric acid has two centres of chirality, there are only 3, not 4, stereoisomers. The third stereoisomer is achiral - it is described as being meso.

The two enantiomers of tartaric acid.
   

Below is meso tartaric acid. Satisfy yourself that the two "enantiomers" are in fact the same molecule. The meso form is achiral - it does not rotate plae polarised light.

The meso form of tartaric acid. Both structures are the same.