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.
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.