Stereochemical

Stereochemical refers to stereochemistry, the branch of chemistry that studies how the three‑dimensional arrangement of atoms in a molecule affects its properties and reactivity. The field focuses on isomers that share the same connectivity but differ in spatial orientation. Stereochemistry distinguishes between configurational isomers, which require bond-breaking to interconvert (such as enantiomers and diastereomers), and conformational isomers, which arise from rotation about single bonds and can interconvert without breaking bonds.

Key concepts include chirality and stereoisomerism. Molecules with a chiral center can exist as two non-superimposable mirror images, called enantiomers, which often have identical physical properties except for the direction they rotate plane-polarized light and their interactions with other chiral environments. Diastereomers are stereoisomers that are not mirror images. Some compounds containing multiple stereocenters can be meso, achiral despite having chiral centers due to internal symmetry. Stereochemical descriptors such as R and S (Cahn–Ingold–Prelog configuration) and E and Z (for double bonds, based on priority of substituents) are used to specify exact configurations.

Methods to determine or infer stereochemistry include optical rotation measurements, chiral chromatography, nuclear magnetic resonance spectroscopy (including coupling constants and NOE data), and X-ray crystallography. Stereochemistry has profound implications in biology and medicine, as biological targets are often chiral and respond differently to each enantiomer. In synthesis, stereoselectivity and enantioselectivity describe the preferential formation of one stereoisomer over others, a central aim of asymmetric synthesis.