Draw and interconvert Fischer projections, Newman projections, sawhorse diagrams, and wedge-dash notation.
Two-dimensional representations of three-dimensional molecular structure — Fischer projections, Newman projections, sawhorse diagrams, and wedge-dash notation — are essential tools for communicating stereochemistry on paper, and fluently converting between them is heavily tested on both USNCO and IChO exams.
Fischer projections represent a molecule as a cross: horizontal lines project toward the viewer, vertical lines project away. This convention, developed originally for sugars, makes it fast to assign D/L configuration by checking whether the lowest carbon on the chain has the reference group on the right (D) or left (L) — distinct from, though often correlated with, the CIP R/S system. Rotating a Fischer projection by 180° in the plane of the page preserves its meaning, but rotating it 90° inverts the apparent configuration, a classic exam trap.
Newman projections view a molecule directly down a specific carbon-carbon bond, showing the front atom's substituents as lines from a center point and the back atom's substituents as lines from a surrounding circle. This projection is ideal for analyzing conformational analysis: eclipsed conformations (front and back substituents aligned) are higher energy due to torsional strain, while staggered conformations are lower energy, with the anti conformation (largest groups 180° apart) typically most stable of all, and gauche conformations (60° apart) intermediate.
Sawhorse diagrams show the same C-C bond from a angled perspective rather than end-on, making it easier to see the full 3D shape of both carbons simultaneously. Wedge-dash notation — solid wedges toward the viewer, dashed wedges away — is the standard for showing stereocenters in ordinary structural drawings, and correctly assigning R/S configuration from a wedge-dash structure using CIP priority rules is a fundamental stereochemistry skill.
This projection formula lab lets you draw a molecule once and instantly interconvert between all four representations, assign R/S configuration step by step, and practice D/L notation for carbohydrates — building fluency across every projection style you'll encounter on exams.