Fischer projections are a 2D representation of the atomic connectivity and stereochemistry of 3D molecules. Originally developed in 1891 by Emil Fischer, they help visualize carbohydrates, amino acids, and other compounds in Organic and Biochemistry.
Fischer projections of glucoseHere we’ve got Fischer projections of L- and D-glucose. They’re enantiomers of each other, and there are plenty of other stereoisomers of the monosaccharide.
The minimum variation required to be considered a stereoisomer is to swap the horizontal groups in one chiral center, so that means that glucose has tons of diastereomers.
L-galactose and D-galactoseGalactose, shown above, differs from glucose in the configuration of just one chiral center. It's got the same chemical formula and atomic connectivity as glucose but different stereochemistry, so it's a diastereomer.
Visualizing the caterpillar methodIt’s fairly straightforward to convert bondline structures to Fischer projections and vice-versa using the caterpillar method as seen above. Double checking your Fischer projection’s R and S to see if it’s been drawn properly is always good practice!
There are many other ways to represent three-dimensional molecules including the Haworth, sawhorse, and Newman projections.
