Absolute configuration

An absolute configuration in stereochemistry is the spatial arrangement of the atoms of a chiral molecular entity (or group) and its stereochemical description e.g. R or S.

Absolute configurations for chiral molecules are traditionally obtained by X-ray crystallography but only when the compound crystallises in one of the 65 Sohncke Groups (Chiral Space Groups). Alternative techniques are Optical rotatory dispersion, vibrational circular dichroism and the use of chiral shift reagents in proton NMR.

In step two the assignment of R or S is based on the Cahn-Ingold-Prelog priority rules.

Absolute configurations are also relevant to characterization of crystals.