Stereochemical Terminology Flashcard

Absolute configuration
A designation of the position or order of arrangement of the ligands of a stereogenic unit in reference to an agreed upon stereochemical standard
Achiral
Not chiral. A necessary and sufficient criterion for achirality in a rigid molecule is the presence of any improper symmetry element
Achirotopic
Opposite of chirotopic (chirotopic: the term used to denote that an atom, point, group, face, or line resides in a chiral environment)
Anomers
Diastereomers of glycosides or related cyclic forms of sugars that are specificially epimers at the anomeric carbon (C1 of an aldose or C2,C3,etc. of a ketose)
Anti
Modern usage is to describe relative configuration of two stereogenic centers along a chain. The chain is drawn in zigzag form, and if two substituents are on opposite sides of the plan of the paper, they are designated anti.
Anticlinical
A term describing a conformation about a single bond. In A-B-C-D, A and D are anticlinical if the torsion angle between them is between 90 and 150 or -90 and -150.
Antiperiplanar
A term describing a conformation about a single bond. In A-B-C-D, A and D are antiperiplanar if the torsion angle between them is +150 to -150.
Apical = axial, basal = equatorial
Terms associated with the bonds and positions of ligands in trigonal bipyramidal structures
Asymmetric
Lacking all symmetry elements. All asymmetric molecules are chiral
Asymmetric carbon atom
Traditional term used to describe a carbon with four different ligands attached. Not recommended in modern usage.
Atactic
A term describing the relative configuration along a polymer backbone. In an atactic polymer, the stereochemistry is random–no particular pattern or bias is seen.
Atropisomers
Stereoisomers (can be either enantiomers or diastereomers) that can be interconverted by rotation about single bonds and for which the barrier to rotation is large enough that the stereoisomers can be separated and do not interconvert readily at room temperature.
Chiral
Existing in two forms that are related as non-congruent mirror images. A necessary and sufficient criterion for chirality in a rigid molecule is the absence of any improper symmetry elements
Chiral center
Older term for a tetracoordinate carbon or similar atom with four different substituents. More modern, and preferable, terminology is “stereogenic center” (or “stereocenter”).
Chirotopic
The term used to denote an atom, point, group, face, or line resides in a chiral environment
Cis
Describing the stereochemical relationship between two ligands that are on the same side of a double bond or a ring system. For alkenes only, Z is preferred.
Configuration
The relative position or order of the arrangement of atoms in space that characterizes a particular stereoisomer
Conformers or conformation isomers
Stereoisomers that are interconverted by rapid rotation about a single bond
Constitutionally heterotopic
The same groups or atoms with different connectivities
D and L
An older system for identifying enantiomers, relating all stereocenters to the sense of chirality of D- or L-glyceraldehyde. Generally not used anymore, except for biological structures such as amino acids and sugars.

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