Organic Chemistry: Stereochemistry

Fischer Projections

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:

1. 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.
2. A Fischer projection may not be rotated by 90 degrees. Such a rotation typically changes the configuration to the enantiomer.
3. To find the enantiomer of a molecule drawn as a Fischer projection, simply exchange the right and left horizontal bonds.
4. 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