Translating Fischer Projections

Translating Fischer Projections

Fischer projections were invented by the German sugar chemist Emil Fischer to simplify displaying the stereochemical relationships among carbohydrate structures.

• Fischer projections may not be lifted from the plane of the paper, nor rotated by other than 180 degrees.
• They also are supposed to be drawn only with the most highly oxidized carbon at the top, and the "main" carbon chain vertically oriented.

 Translation  of glyceric acid:





To view the main chain as vertical and completely aligned, implies that the sideways projecting bonds of the Fischer structure are actually coming up out of the the page, whereas the vertical bonds are oriented behind it.

• Making this change turns the Fischer at left into the dash-wedge at center.
• A 90 degree rotation to the right produces a more familiar view of the molecule.

That the Fischer projection formally places the molecule into an all eclipsed conformation is shown in the second example, where we step through the transformation from Fischer to dash-wedge for a molecule having three chiral centers.

• Once translated, the structure can be rotated easily into a fully staggered conformation by simply turning the two end chiral centers 180 degrees.
• Such a manipulation is not permitted with a Fischer projection because it changes the absolute configuration.