3.5: Newman Projections
Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers. Hence, various notations are used to identify and represent these conformers.
When rotated by 45° perpendicular to the molecular axis, the dash-wedge structure arrives at the sawhorse structure. Here, the molecule is observed at an oblique angle, and all the groups and bonds are visible to the observer. The Newman projection is obtained upon a 90° degree rotation of the dash-wedge structure. It is an end-on representation where the molecule is viewed along the bond of interest, a projected bond. The atom farther from the observer is represented by a circle, and the atom closer to the observer is denoted as the center of the circle. The bonds attached to these farther and closer atoms are drawn from the circle’s periphery and center, respectively. The dihedral angle between the bonds connected to nearer and farther atoms determines the structure of a conformer.