Assign R or S configuration to any stereocenter with step-by-step CIP priority rules.
Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and how that arrangement affects physical and chemical properties. It is a major topic in IChO preparatory problems, appears in USNCO national exam free response questions, and is increasingly represented in advanced AP Chemistry coursework.
Chirality is the fundamental concept: a molecule is chiral if it is non-superimposable on its mirror image, like left and right hands. The most common source of chirality is a tetrahedral carbon bearing four different substituents — called a stereocenter or chiral center. Molecules with one stereocenter exist as a pair of enantiomers.
The Cahn–Ingold–Prelog (CIP) priority rules assign R or S configuration to each stereocenter. Step 1: rank the four substituents by atomic number (highest priority = 1). Step 2: orient the molecule with priority-4 pointing away from you. Step 3: trace a path from 1 → 2 → 3. Clockwise gives R (rectus); counterclockwise gives S (sinister). When two atoms attached to the stereocenter are the same element, compare the next atoms outward — the "phantom atom" rule handles double bonds.
Diastereomers are stereoisomers that are not mirror images of each other. A compound with n stereocenters has a maximum of 2ⁿ stereoisomers. Meso compounds contain stereocenters but are achiral overall due to an internal plane of symmetry — a classic exam trap that often catches students off-guard.
Fischer projections represent stereochemistry in two dimensions: horizontal bonds project toward the viewer, vertical bonds project away. Newman projections depict conformation by viewing down a C–C bond. Sawhorse diagrams show the 3D perspective from a slight angle. Converting between these representation types is heavily tested in USNCO and IChO problems.
This stereochemistry solver provides step-by-step CIP rule application, interconversion between all projection types, meso compound detection, and optical rotation concepts — the complete toolkit for mastering three-dimensional molecular structure.