Atropisomerism

Atropisomerism is stereoisomerism caused by restricted rotation about a single bond. The resulting conformers interconvert slowly enough to be distinguishable as stereoisomers.

Rotational barrier: The energy difference between a rotational transition state and a stable molecular conformation. A sufficiently high barrier makes rotation slow enough for atropisomers to persist.
Stereoisomerism: Isomerism in which compounds have the same connectivity but differ in the spatial arrangement of atoms. Atropisomerism is one way stereoisomers arise without changing molecular connectivity.
Atropisomeric drug: A pharmaceutical compound whose biologically relevant stereoisomers arise from restricted rotation about a single bond. Its atropisomeric forms may differ in potency, safety, or pharmacokinetics.
Cis–trans isomerism: Geometric isomerism in which substituents occupy different relative positions across a bond or ring. It commonly arises from restricted rotation, but its stereoisomers are defined by geometric arrangement rather than atropisomeric persistence.
Steric hindrance: The resistance to molecular arrangements caused by atoms or groups occupying nearby space. Crowding around the rotating bond often raises the barrier that produces atropisomerism.
Conformational isomerism: Isomerism arising from different molecular conformations accessible through rotations about single bonds. Atropisomers are conformers whose interconversion is unusually slow.
Atroposelective synthesis: A synthesis that preferentially forms one atropisomer over another. Controlling the rotationally restricted axis can set a product's stereochemistry.
E/Z notation: A system for specifying the relative positions of higher-priority substituents across a double bond. It describes alkene geometry, not stereoisomerism caused by restricted rotation about a single bond.
Biaryl compound: A compound containing two aromatic rings joined by a carbon–carbon bond. Crowding between ortho substituents can restrict rotation around the bond joining its rings.
Enantiomer: One of a pair of stereoisomers that are non-superimposable mirror images. Chiral atropisomers can exist as enantiomeric pairs.

Linked from 11 pages