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Three-Dimensional Representations

Assigning Priorities

Determining Stereochemical Relationships

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Three-Dimensional Representations: Newman Projections

Newman Projections are used mainly for determining conformational relationships. Recall that conformers are molecules that can be converted into one another by a rotation around a single bond. Newman Projections are also useful when studying a reaction involving prochiral molecules that have a double bond, in which the addition of a new group creates a new stereocenter.

In this notation, you are actually viewing a molecule by looking down a particular carbon-carbon bond. The front carbon of this bond is represented by a dot, and the back carbon is represented by a large circle. The three remaining bonds are drawn as sticks coming off the dot (or circle), separated by one another by 120 degrees. A Newman Projection can be drawn such that the groups on the front carbon are staggered (60 degrees apart) or eclipsed (directly overlapping) with the groups on the back carbon. Below are two Newman Projections of ethane, C2H6. The structure on the left is staggered, and the structure on the right is eclipsed. These are the simplest Newman Projections because they have only two carbons, and all of the groups on both carbons are identical.

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