enantiopure

Enantiopure, or enantiomerically pure, describes a substance that contains essentially only one enantiomer of a chiral molecule. A chiral molecule has non-superimposable mirror-image forms, typically labeled as R and S. In an enantiopure sample, the amount of the opposite enantiomer is negligible, whereas a racemic mixture contains roughly equal amounts of both enantiomers. The degree of purity is usually expressed as enantiomeric excess (ee), calculated as ee = |R − S| / (R + S) × 100%.

Enantiopure materials are typically prepared through chiral resolution of a racemate or by asymmetric synthesis that uses chiral catalysts or reagents to preferentially form one enantiomer. Enantioselective catalysis is widely used in pharmaceutical and fine chemical synthesis to improve potency, safety, and pharmacokinetic properties. The term can also refer to samples with very high ee, often approaching 99% or higher, depending on the context and regulatory needs.

Analytical methods to assess enantiopurity include polarimetry (measuring optical rotation), chiral high-performance liquid chromatography or gas chromatography, and circular dichroism. Nuclear magnetic resonance with chiral shift reagents can also aid in distinguishing enantiomers.

Applications of enantiopure compounds are prominent in medicine, where different enantiomers can have distinct biological activities, and in flavors, fragrances, and materials science. Achieving and maintaining enantiopurity can be challenging due to racemization under certain conditions, so stability and storage considerations are important in practical use.