Newman Projections
Newman projection is a short hand way to represent a molecule.
You can imagine standing in front of the molecule and looking at carbon 1 like the person on the top left. The carbon has group a on top as shown in the Newman projection, group b to the right and group c to the left. Behind carbon 1 is carbon 2. The person can't see it but can see the attachment that it has: f to the left, e to the left and d at the bottom. When the groups on the two carbons are spread out, the conformation is called staggered. We can freely rotate around a single bond, moving the groups on the second carbon right behind the groups on the first carbon. When the groups are right behind one another, like the second molecule, the conformation is called eclipsed.
Staggered conformation is always more stable and lower in energy than eclipsed!!!
Conformations of Butane
Let's take a look at some of these conformations. If in a staggered conformation, two groups are next to each other, it is called GAUCHE and is higher in energy due to steric strain ( two groups bumping into one another) (structures B and F). If the two big groups are opposite one another in a staggered conformation, it is called ANTI and is lower in energy (structure D).
If two bulky groups are right next to each other in an eclipsed conformation (structure A), this causes the conformation to be less stable and higher in energy.
To go from one conformation to another, I simply rotated the back carbon as shown in the picture above.
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