Pseudochirality

Pseudochirality or pseudoasymmetry occurs when chirality is reliant only on other atoms in the molecule that are chiral. Most commonly, a stereocenter with 2 identical substituents differing only in having opposite chirality are bonded to the same stereocenter. For example, if substituents 1, 2, 3 and 4 are bonded to a single carbon and substituents 3 and 4 are the same only differing in that 3 is R and 4 is S, the molecule would be pseudochiral. This is because if substituents 3 and 4 have the same chirality, there would no longer be 4 different substituents bonded to the center atom which disestablishes the center atom as a stereocenter and renders the molecule unable to be chiral.[1][2] When an atom is pseudochiral, it's nomenclature is (r/s) instead of (R/S). An important note is that R takes priority over S in assigning CIP priority. In the pictured example the stereocenter C(s) is bonded to Cl, H, C(R) and C(S). Since the two carbons are opposite in terms of R/S, they count as two distinct and differing substituents this makes the stereocenter C(s) pseudochiral. Pseudochirality can affect the effectiveness of some drugs.[3][4]

Axial Pseudochirality

Pseudochirality can also exist in the form of axial chirality most commonly in atropisomers, allenes and alkylidene cycloalkanes.

References

  1. ^ Gold, Victor, ed. (2019). The IUPAC Compendium of Chemical Terminology: The Gold Book (4 ed.). Research Triangle Park, NC: International Union of Pure and Applied Chemistry (IUPAC). doi:10.1351/goldbook.p04921.
  2. ^ Sbîrnă, L.-S., Moldovan, C. S., & Ciuperceanu, M. (2025). Pseudo-chirality – an issue that should not be misdefined, misinterpreted or treated as a “pseudo-matter” nor in describing stereochemistry neither in drug design. Annals of the University of Craiova, Chemistry Series, 51(1), 28–36. https://chimie.ucv.ro/wp-content/uploads/2025/11/M4_ANALE-CHIMIE.-VOLUM-51-Nr.-1-2025-28-36.pdf
  3. ^ Chen, Yang; Chen, Jiayan; Zhu, Shifa (2025-06-25). "Rh(I)-Catalyzed Modular Synthesis of Axially Chiral Alkylidene Azacycloalkanes". ACS Central Science. 11 (6): 899–909. doi:10.1021/acscentsci.5c00232. ISSN 2374-7943. PMC 12203264. PMID 40585798.
  4. ^ Nourse, James G. (1975). "Pseudochirality". Journal of the American Chemical Society. 97 (16): 4594–4601. doi:10.1021/ja00849a022. ISSN 0002-7863. Retrieved December 22, 2025.
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