In this tutorial, you will learn what Newman projections are and why they are useful in organic chemistry. You will also learn the steps to drawing one!
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What are Newman Projections?
Newman projections are drawings used to help visualize the 3-dimensional structure of an organic molecule. They represent a side view of a C-C alkane, or a single bond, as well as its side groups in each direction; they help to easily visualize the orientation of all the atoms or molecules bonding to the carbon represented by lines, dashes, or wedges.
Let’s look at an alkane and its Newman projection:
The arrow indicates the angle where we are looking through. Each Newman projection represents the bond between 2 carbons by a dot (front carbon) and a circle (back carbon). The side groups and their placements are specific to the alkane you are analyzing.
Staggered vs. Eclipsed Conformations
Because of the free rotation around single bonds, there are various conformations for a single molecule. In fact, there could be up to 6 different Newman projections drawn for a single molecule: 3 staggered conformations and 3 eclipsed conformations! Each conformation is a 60-degree rotation – six 60-degree rotations equals the full 360 degrees of a circle.
Staggered conformations are the lower energy arrangements. This is because each side group is 60 degrees apart from the others, so there is no torsional strain; the side groups of the front carbon are maximally spread out from those of the back carbon, which decreases the possibility of interaction.
Eclipsed conformations are higher in energy than staggered due to bond straining. In this arrangement, the side groups of the front carbon are directly in front of the side groups of the back carbon; so when looking from the side you would only see the side groups of the closer carbon.
How to draw a Newman Projection
1. Find the side view you are going to be using
When looking at the alkane, you want to decide which bond you will be looking at and from which side. This will usually be indicated by an arrow showing the front carbon, or the dot of your Newman projection.
2. Draw the skeletal structure
Each Newman projection starts with a circle and a dot in the middle representing the two carbons, so draw that as a base.
3. Draw side groups of front carbon
Analyzing the alkane given, you can draw the Newman projection of the front carbon first. If a side group is on a wedge, that means it is coming out of the paper (towards you), so that can be written as a line toward the right. Reversely, a side group on a dash means it is going into the paper (away from you), so that can be written as a line toward the left. A side group represented by a simple line, meaning the molecule is in the plane of the page, is going to be written straight up or down.
If the side group written on a line is going downward, then draw that line going down from the carbon dot, along with the lines going left or right. Since the lines should be 60 degrees apart, this should look like a Y shape.
On the other hand, if the side group on a line is going upward, the line on the Newman projection should be directly up; this should create an upside-down Y shape with the other side groups.
4. Draw side groups of back carbon
You have to think about which conformation you will be drawing if it is not given. If you are drawing the staggered conformation, all the side groups will be evenly spaced from each other; if the eclipsed confrontation is being drawn, the side groups of the front will be 60 degrees from each other, with the side groups of the back directly behind. With this in mind, you can draw the side groups coming from the larger circle, or the back carbon.
5. Draw the other conformations!
By rotating one of the carbons, you can create up to six different conformations of the alkane!