What is the process to convert Sawhorse Projections into Fischer Projections? Can I get an example?

1 Answer
Nov 29, 2015

Well, first let's construct a regular molecule, and then proceed to its sawhorse projection, and from there draw out its Fischer projection.

The original molecule:

Then, what you can do is rotate it so it's more diagonally oriented.

For the eclipsed sawhorse, I've rotated the front/left bond to orient the hydride axially, and then for the staggered sawhorse, I've modified the eclipsed sawhorse by rotating the rear/right carbon #60^@# CCW.

Here, you can more easily see staggered/eclipsed conformational relationships, anti/synperiplanar conformations, etc.

And to get this to look like a Fischer projection, just imagine flattening the result by mentally pushing atoms down onto one plane, as if you had a molecular model in front of you. Notice how the equatorial left atoms are then on the left, the equatorial right atoms are then on the right, and the axial atoms are then facing up and down.

Here, there is a loss of information about anti/synperiplanar, as well as staggered/eclipsed relationships, but it's fast to draw. Sometimes though, chirality labels are harder to maintain when comparing eclipsed vs. staggered.