Newman-projecties

A common way of representing a three-dimensional structure of a molecule on a two-dimensional surface is using the dash-wedge notation.

In this notation, solid lines represent bonds lying in the same plane; solid wedges indicate bonds coming out of the plane, and dashed wedges represent bonds situated behind the plane.

In an organic molecule like 1,2-dibromo-1,2-dichloroethane,  single bonds — due to the sigma nature of their orbital overlap — can rotate freely. Therefore, the molecule can adopt different shapes without breaking the bonds.

The three-dimensional temporary shapes generated by such rotations are called conformations, and each structure is referred to as a conformer.

Now consider the molecule’s dash-wedge notation.

A 45° rotation about the molecule’s vertical axis generates the sawhorse projection. The molecule is viewed from an oblique angle, with all atoms and bonds being visible.

In comparison, a 90° rotation of the molecule gives rise to a planar projection called the Newman projection. 

In this, the molecule is viewed end-on, along the C-C bond — called the projected bond. The circle represents the carbon atom farther from the observer, and the bonds connected to