Gauche
Definition: A conformation in which substituents on adjacent carbons are separated by a dihedral angle of approximately 60°.
Context: Important in determining conformational energy and intramolecular interactions such as the gauche effect.
Example: Gauche butane conformation is less stable than anti but more stable than eclipsed.
Related Terms: Anti; Synclinal; Conformation; Newman Projection.
Reference: Eliel & Wilen (1994).
Geminal
Definition: Refers to two substituents attached to the same atom, typically a carbon.
Context: Geminal dihalides or diols exhibit distinct reactivity compared to vicinal analogs.
Example: Geminal dichlorides (R?CCl?) vs vicinal dichlorides (RCHCl–CH?Cl).
Related Terms: Vicinal; Substituent; Structural Isomer.
Reference: IUPAC Gold Book (2019).
Geometric Isomerism
Stereoisomerism due to restricted rotation (double bonds, rings).
Context: Controls pharmacology through spatial disposition of groups.
Example: cis/trans-platin complexes.
Related Terms: E/Z Isomerism, Ring Conformations.
Reference: IUPAC Gold Book.
GPCR Stereoselectivity
Enantiomer-dependent binding and signaling at GPCRs.
Context: Explains potency and bias differences across enantiomers.
Example: L- vs D-ligands at opioid receptors.
Related Terms: Stereopharmacology, Eutomer/Distomer.
Reference: Kenakin, Pharmacology Primer (2019).