Chiralpedia

Enantiomer

Paired Concept: Diastereomer

Definition: One of a pair of non-superimposable mirror-image stereoisomers.
Context: Enantiomers may differ in PK/PD and toxicity; single-enantiomer drugs are often preferred.
Example: S-ibuprofen (eutomer) vs R-ibuprofen (distomer).
Related Terms: Racemate, Eutomer, Distomer.
Reference: Morrison & Boyd, Organic Chemistry.

Enantiomeric Excess (ee)
Definition: The absolute difference in enantiomer fractions (|%R − %S|).
Context: Standard QC metric for chiral purity in pharma.
Example: 70% R, 30% S → 40% ee.
Related Terms: Enantiomeric Ratio, Optical Purity.
Reference: IUPAC Gold Book.

Enantiomeric Ratio (er)
Definition: The ratio of enantiomers, typically expressed as R:S.
Context: Preferred over ee for statistical modeling and kinetics.
Example: 98:2 e.r. for a product.
Related Terms: Enantiomeric Excess, dr.
Reference: IUPAC Gold Book.

Enantiomerization
Definition: Interconversion between enantiomers via bond rotation or reversible processes.
Context: Defines shelf-life and handling conditions for atropisomeric drugs.
Example: Biaryl axis rotation over barrier ΔG‡.
Related Terms: Racemization, Barrier to Rotation.
Reference: IUPAC Gold Book.

Enantiopure (Enantiomerically pure)

Paired Concept: Scalemic Mixture | Racemic Mixture

Definition: A chiral substance that contains only one enantiomer, with an enantiomeric excess (ee) of essentially 100%. In an enantiopure sample, the opposite enantiomer is absent or present only in negligible trace amounts.
Context: Enantiopure compounds are highly valued in pharmaceutical, agrochemical, and fine chemical industries because the two enantiomers of a chiral molecule can exhibit markedly different biological, pharmacological, toxicological, or environmental behaviors. Advances in asymmetric synthesis, chiral resolution, and chiral chromatography have enabled the production of enantiopure substances on both laboratory and industrial scales. Regulatory agencies often require separate evaluation of individual enantiomers when stereochemistry significantly influences efficacy or safety.
Example: The proton-pump inhibitor Esomeprazole consists exclusively of the S-enantiomer of omeprazole and is therefore an enantiopure drug. Similarly, Levofloxacin is the enantiopure S-enantiomer of ofloxacin.
Related Terms: Enantiomer, Enantioenriched, Racemate, Chiral Purity, Enantiomeric Excess (ee), Asymmetric Synthesis, Chiral Resolution.
Reference: Eliel, E. L., Wilen, S. H., & Doyle, M. P. (1994). Basic Organic Stereochemistry. New York: John Wiley & Sons. ISBN: 978-0471374993; Jacques, J., Collet, A., & Wilen, S. H. (1994). Enantiomers, Racemates, and Resolutions. Krieger Publishing Company, Malabar, Florida. ISBN: 978-0894648282; Carey, F. A., & Sundberg, R. J. (2007). Advanced Organic Chemistry, Part A: Structure and Mechanisms (5th ed.). Springer. ISBN: 978-0387448979; IUPAC Compendium of Chemical Terminology (Gold Book). Definition of "Enantiomerically Pure" and related stereochemical terminology. Published by the International Union of Pure and Applied Chemistry.