Basic Organic Nomenclature
7. Stereochemistry (iii)
|Before looking at the way in which enantiomers are
named, it is necessary to be able to illustrate stereoisomers on
two-dimensional surfaces. To overcome the diffuculty of representing
three-dimensional structures in two dimensions, chemists have invented
several different approaches, each valuable to illustrate certain
The approaches most commonly used, and introduced here, are:
Wedge diagrams.In this method, the spacial orientation at a particular atom in the molecule is shown using wedge lines for the bonds:
a filled-in wedge denotes a bond coming out
of the plane of the paper;
In constructing these diagrams, it is usual to use one filled-in
wedge, one dashed wedge and two simple lines. When using this
combination it is important to realize that the two wedges (and hence
the two simple lines also) must be adjacent to each
other as in:
The diagram is ambiguous if this is not the case!
Illustrate the two enantiomers of 2-bromopropanoic acid using wedge diagrams:
Compare the two diagrams to the 3-dimensional models, and note how
diagrams do indeed represent the two possible enantiomers in that they
represent mirror images of each other.
Make sure that you see the different stereoisomer represented by each diagram.
Observe that the two diagrams can be interchanged by exchanging any two of the groups attached to the chirality centre.
ExercisesTry the following exercises.
Continue illustration conventions with one of the following:
Review More than One Chirality centre.
Next page: R and S nomenclature.
Main index page of MolecularModels.ca.
This document page last modified (mo/day/year) :