The Newman Projection is an important skill for every organic chemistry student. Not only does it provide you with another perspective of organic compounds, but it also gives you a means to analyze the conformational energy of a molecule. In this article I will give you a quick introduction to the energy diagram of a Newman Projection.
Unlike a sawhorse projection in which a molecule is read left to right or right to left, in a Newman Projection the molecule is angled so that you wind up looking right down the bond between 2 carbon atoms. This allows you to envision one carbon directly in front of you, and the second carbon behind it.
In viewing a molecule from this angle you get a clear picture of how the substituents interact with each other. You can see how close they are along with any potential negative interactions.
Just like people, atoms have a comfort zone or ‘personal space’ and get very unhappy if that space is invaded.
When analyzing the Newman Projections there are 2 conformations to classify; Staggered and Eclipsed
The Staggered Conformation
When the carbon atoms are held in a way that their substituents do not directly overlap each other, this is called a staggered Newman Projection. When looking at the molecule you will recognize the pattern of front, back, front, back, front, back. This allows each atom or group of atom a bit of space and therefor stability. This will give you the lowest set of energies within an energy diagram.
The Eclipsed Conformation
When your molecule is held in a way such that the substituents on the rear carbon are directly behind the substituents on the forward carbon, this is considered an eclipsed conformation.
In this conformation the atoms or atom groups are too close to each other making the molecule somewhat unstable. The carbon atoms holding these substituents will attempt to ‘bend away’ from each other resulting in all sorts of unfavorable high energies including tension and torsional strain. This results in high peaks on your energy diagram.
A 60 degree rotation will take the molecule from staggered to eclipsed, while another 60 will take it to the next staggered conformation and so on.
This is represented by a series of valleys and hills on the energy diagram which is drawn from 0 degrees followed by 60, 120, 180…
You may choose to start at any conformation since molecules rotate freely in space.