Newman Projections, Sawhorse Representations & Wedge & Dash Models

Instructor: Laura Foist

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

By looking at something from multiple perspectives we can understand different things about it. In this lesson we will learn about the Newman projections, the sawhorse representations, and the wedge and dash models for representing chemical molecules.

Different Perspectives

Have you ever looked at the same object from several angles and realized it looked different from each one? Depending on how we look at an object, certain aspects may become more or less apparent, changing the way that it looks and possibly offering a better understanding.

We have several different ways to represent chemical molecules that give us alternate angles views. With each representation we learn more. Today we will learn about three of these representations:

  • Wedge and dash models
  • Newman projections
  • Sawhorse representations

Wedge and Dash Models

You are probably most familiar with the wedge and dash models, as they are used fairly frequently to represent chemical molecules. The wedge and dash model is used for picturing the 3D molecule. It uses a wedge to show a bond coming out of the paper (or up) and a dash to show a bond going into the paper (or down).

This model is typically used for chiral molecules (molecules with 4 distinct bonds), but it can be used for any type of molecule.

Let's look at the molecule 3-chloro-2-butanol:


3 chloro 2 butanol


In the general method for drawing the molecule (and even with the basic name) we have no way of knowing the orientation of each bond. There are four enantiomers of this molecule. In other words, four ways that the bonds of the molecule may actually be bound together when we look at the 3D representation:


Each chiral carbon can be identified as R or S depending on how the atoms are connected
3D of each enantiomer


When we look at these 3D representations we can see that around both chiral carbons (carbon 2 and 3) the hydrogen is either pointing out of the page (up) or into the page (down). So, we can draw the wedge and dash molecules for each of these enantiomers:


4 enantiomers wedge and dash


The nice thing about the wedge and dash model is that we can easily see the entire molecule and have pictures that we can easily imagine as a 3D representation. This model best represents the 3D molecule in a 2D state.

Newman Projections

The Newman projections are used seeing how the bonds interact with each other. They are interesting because, in this case, we are looking straight down the bond between two carbon atoms. Therefore, the first carbon ends up completely blocking the second carbon from view:


When we look down the bond the carbon in the back is completely hidden
3D Newman


But, this projection allows us to see how the different attachments on each carbon will interfere with each other. In order to draw it, we simply draw the two carbons using a circle for the back carbon and a dot for the front carbon. We can then draw the bonds coming out from each carbon:


Newman projection


Drawing each of the enantiomers of 3-chloro-2-butanol, we can examine some of the stability of each enantiomer. We can easily convert between the wedge and dash models and the Newman projections by putting the straight lines opposite each other (anywhere on the model), then the atoms coming out of the page need to be on the same side as well as the atoms going into the page.


Newman enantiomers


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