text: The stability of individual atropisomers is conferred by the repulsive interactions that inhibit rotation. Both the steric bulk and, in principle, the length and rigidity of the bond connecting the two subunits contribute. Commonly, atropisomerism is studied by dynamic nuclear magnetic resonance spectroscopy, since atropisomerism is a form of fluxionality. Inferences from theory and results of reaction outcomes and yields also contribute.
  Atropisomers exhibit axial chirality (planar chirality). When the barrier to racemization is high, as illustrated by the BINAP ligands, the phenomenon becomes of practical value in asymmetric synthesis. Methaqualone, the anxiolytic and hypnotic-sedative, is a classical example of a drug molecule that exhibits the phenomenon of atropisomerism.