Axial chirality

Bonding to asymmetric carbon has the form Cabcd where a, b, c, and d must be distinct groups.

Similarly, chiral atropisomers of the form abC−Ccd may have some identical groups (abC−Cab), as in BINAP.

The enantiomers of axially chiral compounds are usually given the stereochemical labels (Ra) and (Sa),[1] sometimes abbreviated (R) and (S).

[5][1] Enantiomers having helicity may labeled by using the prefix notation (P) ("plus") or Δ (from Latin dexter, "right") for a right-handed helix, and (M) ("minus") or Λ (Latin levo, "left") for a left-handed helix.

This notation can also be applied to non-helical structures having axial chirality by considering the helical orientation of the Cahn–Ingold–Prelog group rankings of the "front" groups compared to the "back", when viewed from either direction along the axis.