Newman projection
/ NEW-mun /
A Newman projection is a way of drawing a molecule by looking straight down one of its bonds, like sighting along the barrel of a gun. It turns the messy three-dimensional question 'how are the two ends of this bond rotated relative to each other?' into a simple flat picture, which is why it is the standard tool of conformational analysis.
Here is how to read it. You choose one carbon-carbon bond and view the molecule end-on along it. The front carbon is drawn as a dot with three bonds radiating from it (a Y or a peace sign); the back carbon, hidden directly behind, is drawn as a large circle with its three bonds poking out from the rim. The angle between a front bond and a back bond — the dihedral or torsion angle — is exactly what you twist when you rotate, and the projection makes that angle visible at a glance.
With this view, the difference between conformations leaps out. When the front bonds sit exactly in front of the back bonds (zero degrees apart) the molecule is eclipsed and strained; when they are offset by sixty degrees, nestled in the gaps, it is staggered and relaxed. Newman projections are how chemists compare staggered versus eclipsed, anti versus gauche, and reason about which way a molecule will prefer to sit.
For ethane, the staggered Newman projection looks like a six-pointed star (front and back bonds alternating every 60 degrees); the eclipsed one looks like a three-armed shape with front and back bonds overlapping.
Front carbon = dot with three lines; back carbon = circle with three lines; the offset angle is the conformation.
A Newman projection shows one bond's rotation, not the whole molecule's stereochemistry. The back atom is a circle only because it is hidden behind the front atom, not because it is a ring.