Chiralpedia

D-(Dexter, Right)
Definition: A stereochemical prefix denoting a configuration relative to D-glyceraldehyde, not the direction of optical rotation.
Context: Used in carbohydrate and amino acid nomenclature to define absolute configuration based on Fischer projection.
Example: D-glucose corresponds to the configuration of D-glyceraldehyde.
Related Terms: L-; Fischer Projection; Absolute Configuration.
Reference: Fischer, E. "Einfluss der Configuration auf die Wirkung der Enzyme." Ber. Dtsch. Chem. Ges. 24, 1836-1845 (1891).

Deracemization
Definition: Conversion of a racemic mixture to an enantiopure product without external chiral source.
Context: Strategic for late-stage purification and process intensification.
Example: Viedma ripening, enzymatic deracemization.
Related Terms: Viedma Ripening, Absolute Asymmetric Synthesis.
Reference: Blackmond, Angew. Chem. (2010).

Dextro-(d, +)

Associated Concept: Levo- (l, –)

Definition: Denotes a compound that rotates plane-polarized light to the right (clockwise).
Context: Optical rotation descriptors are experimental and distinct from R/S configuration.
Example: D-(+)-glucose.
Related Terms: Levo-, Optical Activity, Specific Rotation.
Reference: IUPAC Gold Book.

Diastereomer (Diastereoisomer)

Associated Concept: Enantiomer

Definition: Stereoisomers not related as mirror images.
Context: Often differ in physical properties, enabling separation and selective synthesis.
Example: Erythro vs threo diols.
Related Terms: Enantiomer, Relative Configuration.
Reference: Eliel & Wilen (1994).

Diastereomeric Excess (de)
Definition: Absolute difference between diastereomer fractions.
Context: QC metric when diastereomers are formed.
Example: 80% syn, 20% anti → 60% de.
Related Terms: dr, Stereoselectivity.
Reference: IUPAC Gold Book.

Diastereomeric Ratio (dr)
Definition: Ratio of diastereomers formed in a reaction.
Context: Guides optimization of diastereoselective steps.
Example: 95:5 syn:anti aldol product.
Related Terms: Diastereomeric Excess, Stereoselectivity.
Reference: IUPAC Gold Book.

Diastereotopic

Associated Concept: Enantiotopic

Definition: A term describing two identical atoms, groups, or faces within the same molecule that are related by neither symmetry nor mirror symmetry and whose replacement or reaction leads to diastereomers rather than enantiomers.
Context: Diastereotopic groups are chemically or magnetically non-equivalent because they exist in different stereochemical environments. They frequently occur in molecules containing an existing stereogenic center or another stereogenic element. Diastereotopic atoms or groups often exhibit different chemical reactivities and produce separate signals in NMR spectroscopy, making the concept essential in stereochemistry, structural elucidation, and asymmetric synthesis.
Example: In (R)-2-butanol, the two hydrogen atoms of the adjacent CH? group are diastereotopic. Replacing one hydrogen rather than the other generates diastereomeric products. Consequently, these hydrogen atoms resonate at different chemical shifts in the ¹H NMR spectrum.
Related Terms: Homotopic, Enantiotopic, Prochirality, Diastereomer, Stereotopicity, Chiral Center.
Reference: Eliel, E. L., Wilen, S. H., & Doyle, M. P. (1994). Basic Organic Stereochemistry. New York: John Wiley & Sons. ISBN: 978-0471374993; Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). Oxford University Press. ISBN: 978-0199270294; Anslyn, E. V., & Dougherty, D. A. (2006). Modern Physical Organic Chemistry. University Science Books. ISBN: 978-1891389314; International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book) - Entries on stereotopicity, enantiotopic, and diastereotopic.
Key Distinction
Homotopic Groups: Replacement of either group produces identical molecules; chemically and spectroscopically equivalent.
Enantiotopic Groups: Replacement of either group produces enantiomers; equivalent in an achiral environment but distinguishable in a chiral environment.
Diastereotopic Groups: Replacement of either group produces diastereomers; chemically and spectroscopically non-equivalent, even in an achiral environment.
Prochiral Groups: Groups that can become stereogenic after a single substitution or transformation.
Key Insight:
Diastereotopicity arises because the groups occupy different stereochemical environments within the same molecule. Unlike enantiotopic groups, diastereotopic groups are inherently distinguishable and often display different chemical shifts, coupling constants, and reactivities, making them particularly important in NMR spectroscopy, stereochemical analysis, and asymmetric synthesis.

Diaxial Interaction (1,3)
Definition: Steric interactions between axial substituents on cyclohexane separated by one carbon.
Context: Dictates conformational preferences relevant to reactivity.
Example: Axial methyl interactions.
Related Terms: A-Values, Conformation.
Reference: Eliel & Wilen (1994).

Distomer

Associated Concept: Eutomer

Definition: The enantiomer of a chiral drug that exhibits lower desired pharmacological activity or therapeutic potency than its counterpart (the eutomer) at the target receptor or biological system.
Context: The two enantiomers of a chiral drug often differ in their interactions with biological targets because of stereoselective molecular recognition. The distomer may be less active, inactive, possess different pharmacological activity, or, in some cases, contribute to adverse effects or toxicity. However, a distomer is not necessarily undesirable; it may exhibit beneficial pharmacological actions, influence pharmacokinetics, or undergo chiral inversion to the eutomer. The relative potency of the eutomer and distomer is expressed by the eudismic ratio.
Example: R-Ibuprofen is the distomer because it has much lower cyclooxygenase (COX) inhibitory activity than S-ibuprofen, the eutomer. However, R-ibuprofen is partially converted in vivo to the active S-enantiomer by metabolic chiral inversion.
Related Terms: Eutomer, Eudismic Ratio, Enantiomer, Racemate, Chiral Drug, Chiral Inversion, Chiral Switch.
Reference: Ariens, E. J. (1984). "Stereochemistry, a Basis for Sophisticated Nonsense in Pharmacokinetics and Clinical Pharmacology." European Journal of Clinical Pharmacology, 26, 663-668; Ariens, E. J. (1986). "Stereochemistry: A Source of Problems in Medicinal Chemistry." Medicinal Research Reviews, 6(4), 451-466; Nguyen, L. A., He, H., & Pham-Huy, C. (2006). "Chiral Drugs: An Overview." International Journal of Biomedical Science, 2(2), 85-100; Smith, S. W. (2009). "Chiral Toxicology: It's the Same Thing... Only Different." Toxicological Sciences, 110(1), 4-30.
Key Distinction
Distomer: The enantiomer with lower desired pharmacological activity or therapeutic potency.
Eutomer: The enantiomer with the greater desired pharmacological activity or therapeutic potency.
Eudismic Ratio: The ratio of the potency of the eutomer to that of the distomer. Chiral Inversion: Metabolic conversion of one enantiomer into its mirror-image enantiomer (e.g., R-ibuprofen ? S-ibuprofen).

DNA Chirality
Definition: DNA adopts right-handed helices (B-form) with chiral sugar backbone.
Context: Chiral recognition of intercalators and drugs depends on helix sense.
Example: D-sugar backbone in nucleic acids.
Related Terms: Helicity, Stereorecognition.
Reference: Watson & Crick; Voet & Voet (2011).

Double Stereodifferentiation
Definition: Outcome determined by interaction of substrate and reagent chirality (matched/mismatched).
Context: Critical in planning complex multi-stereocenter syntheses.
Example: Aldol with chiral enolate and chiral aldehyde.
Related Terms: Matched/Mismatched, Stereocontrol.
Reference: Seebach (1979).

Dynamic Kinetic Asymmetric Transformation (DYKAT)
Definition: Asymmetric reaction converting a racemic substrate mixture to a single enantiomer product via equilibration.
Context: Converts racemic starting materials fully to one enantiomer product.
Example: Pd-catalyzed allylic substitutions.
Related Terms: DKR, Enantioconvergent Synthesis.
Reference: Kagan, Acc. Chem. Res. (1997).

Dynamic Kinetic Resolution (DKR)

Associated Concept: Kinetic Resolution

Definition: Resolution combined with in situ racemization to yield >50% of the desired enantiomer.
Context: Boosts efficiency in API synthesis.
Example: Lipase DKR of secondary alcohols.
Related Terms: Kinetic Resolution, DYKAT.
Reference: Pellissier, Tetrahedron (2003).

Dynamic NMR (DNMR)
Definition: NMR methods to study exchange processes and barriers (e.g., enantiomerization).
Context: Quantifies ΔG‡ for atropisomer interconversion relevant to stability.
Example: DNMR of hindered biaryls.
Related Terms: Barrier to Rotation, Enantiomerization.
Reference: Sandström, Dynamic NMR (1982).