# What is a Haworth Projection? - Definition, Formula & Examples

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

We often need simple ways to depict molecules while still keeping the important information such as stereochemistry of the bonds. Haworth projections do this with cyclic sugar molecules.

## Purpose of a Haworth Projection

When you think of a 6 sided circular object you probably picture a hexagon. It is a simple shape to draw, and when we see it we immediately know it has 6 points. In chemistry, a hexagon shape will often be used to quickly and simply draw a 6-membered ring, but it doesn't depict the actual molecule very well. In reality, most carbon based 6-membered rings will have bond angles of 109o but a hexagon has bond angles of 120o. Also, a hexagon shows all points in the same plane, while in reality they are in two different planes. The chair conformations depict a 6-membered ring in the most realistic sense, but they are not quick and easy to draw. Thus, another version, the Haworth projection, takes the simplicity of a hexagon while keeping some of the important aspects of the molecule such as the direction that the attachments are oriented on the molecule.

Haworth projections are typically used to depict cyclic sugars. Sugars form a 6-membered ring and they have several stereocenters. In order to distinguish between types of sugars, it is important to have a simple way to draw the sugar molecules while keeping the orientation of the OH attachments. The Haworth projection fulfills this role.

## Formulating the Haworth Projection

Since the Haworth projections are typically used for sugars, we will look at how to formulate the Haworth projection starting with the Fischer projection (the most common method used to depict open chain sugars). Let's start with the most common simple sugar, glucose. We first rotate the bonds around carbon 5 clockwise:

We still have the same molecule as before. We are simply looking at carbon 5 from a different angle. Next, we turn the molecule sideways:

With the molecule sideways it is easier to do steps 3 and 4. For step 3 we simply draw a hexagon, but omit the line connecting point 6 (OH) and point 1 (CHO):

Step 4, we add the OH and CH2groups. If, on the sideways molecule, the OH is pointing down then we draw the line down, and if it is pointing up then we draw a line up. Don't worry about the hydrogen atoms right now:

Step 5, we connect the OH and the carbon 1. Don't worry about where the extra oxygen and hydrogen atoms go right now:

Step 6, we add in the hydrogen atoms on the opposite side from the OH groups:

Step 7, we put the OH group onto carbon 1. Since the carbon-oxygen bond was a double bond, we don't know what side the OH group should be on so we end up with two different molecules:

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