Note: Applicable to macromolecules that are chiral or adopt chiral conformations in the crystal. One example of the former case is the crystal structure in which poly(ʟ-lactide) and poly(ᴅ-lactide) stems coexist in equal numbers, i.e., the so-called polylactide stereocomplex. The second case is much more frequent: it applies to most isotactic vinyl polymer crystal polymorphs where the polymer chains are not intrinsically chiral but adopt helical, and thus chiral conformations. Left-handed helices and right-handed helices are, however, isoenergetic and equiprobable and coexist in equal numbers, often giving rise to centrosymmetric crystals.

Examples: \(\ce{\upalpha\mbox{-}}\) and \(\ce{\upgamma\mbox{-}}\)crystal polymorphs of isotactic polypropylene the rhombohedral crystal polymorph \(R \bar 3 c\) of isotactic polystyrene.