Introduction to Fischer Projections
The wedge and dash representations of
stereochemistry can
often become
cumbersome, especially for large molecules which contain a number of
stereocenters. An alternative way to represent stereochemistry is the Fischer
Projection, which was first used by the German chemist Emil Fischer. The
Fischer Projection represents every
stereocenter as a
cross. The
horizontal line represents bonds extending out of the plane of the page, whereas
the vertical line represents bonds extending into the plane of the page.
Figure %: Drawing Fischer Projections
Manipulations of Fischer Projections
When working with Fischer Projections, keep in mind the following rules:
- Because the "up" and "down" aspects of the bonds don't change, a Fischer
projection may be rotated by 180 degrees without changing its meaning.
- A Fischer projection may not be rotated by 90 degrees. Such a rotation
typically changes the configuration to the enantiomer.
- To find the enantiomer of a molecule drawn as a Fischer projection, simply
exchange the right and left horizontal bonds.
- To determine whether the molecule in Fischer projection is a
meso compound, draw a horizontal line through the center of the molecule and
determine whether the molecule is symmetric about that line.
Figure %: Operations on Fischer projections
