# Introduction to Fisher Projections

5 3 a Fischer intro

Tip: This isn't the place to ask a question because the teacher can't reply.

## Key Questions

• A Fischer projection is a way of showing a three dimensional structure in two dimensions. It shows the absolute configuration at chiral centres.

In a Fischer projection, the longest chain is drawn vertically.

The four bonds to a chiral carbon make a cross, with the carbon atom at the intersection of the horizontal and vertical lines.

The two horizontal bonds are pointing toward the viewer. The two vertical bonds are directed away from the viewer.

Here's how I do it.

#### Explanation:

We must view a wedge-dash formula from the correct angle to convert it to a Fischer projection.

Here's the wedge-dash structure.

We now view the molecule with $\text{C-1}$ at the top and with all chiral carbons closest to our eye.

If we are viewing from above, we must mentally rotate the bonds so that $\text{C-2}$ and $\text{C-4}$ are pointing "up".

When we do this, the wedges become dashes, and the dashes become wedges, as in the picture below.

So the $\text{OH}$ groups on $\text{C-2}$ and $\text{C-4}$ become wedges.

We don't rotate $\text{C-3}$ and $\text{C-5}$, so the bonds to the $\text{OH}$ groups on those atoms remain the same.

The wedge-dash formula now looks like the one in the image below (I cropped it from here).

The wedges are now on the right, and the dashes are on the left.

It is as if we had wrapped the chain around a cylindrical tube.

When you flatten the structure onto the surface of the cylinder, you get the Fischer projection of D-glucose.

• Fischer projections are best used to represent the straight-chain structures of monosaccharides.

A Fischer projection is a drawing of a 3D molecule as a flat structure. The chiral carbons are represented by crossed lines.

In addition to carbohydrates, it is useful for other molecules that have two or more chiral carbons.

Fischer projections are useful for differentiating between enantiomers, diastereomers, and meso compounds.

It is often easier to see an internal plane of symmetry in a Fischer projection.

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