Stereochemistry and stereoisomers

Diastereoisomers

Morrison and Boyd § 4.17, Maitland Jones §5.7
The 3D models used in this page show the compounds in a particular conformation, that differs from the drawings in Morrison & Boyd. The latter are based on drawing convention, with all horizontal bonds pointing in the direction of the reader. Such a structure corresponds to an eclipsed orientation of bonds.
In this web page more realistic 3D models are used, showing e.g. the pentane skeleton in a more stable all-trans conformation. Of course, this choice should not affect the conclusions about the stereochemistry!

In 2,3-dichloropentane we have two carbons with each four different substitituents: C2 and C3.
Therefore, four different structures can be made of 2,3-dichloropentane:
A B C D
Arrange the structures A and B in such a way that they form left and right mirror images. Then try to rotate one structure to make it identical ('superimposable') with the the other.
Next, do the same for C and D.
Finally, follow the same procedure for B and C.

Which structures are mirror images, which are diastereoisomers (=different, neither identical, nor mirror images)?
Assign R/S labels to the chiral centers.
Question:
What is the correct label for the yellow carbon?

R
S

Continue with meso structures.

Back to previous page Back to index To the next page