Term: pseudo-asymmetric carbon atom
https://doi.org/10.1351/goldbook.P04921

Definition:
The traditional name for a tetrahedrally coordinated carbon atom bonded to four different entities, two and only two of which have the same constitution but opposite chirality sense. The r/s descriptors of pseudo-asymmetric carbon atoms are invariant on reflection in a mirror (i.e. r remains r, and s remains s), but are reversed by the exchange of any two entities (i.e. r becomes s, and s becomes r). An example is C-3 of ribaric (C-3 is r) or xylaric acid (C-3 is s) or hyoscyamine (C-3 is r). The hyphen in pseudo-asymmetric may be omitted. P04921.png

Related Terms:
1) constitution (http://doi.org/10.1351/goldbook.C01282).
2) chirality sense (http://doi.org/10.1351/goldbook.C01063).
3) asymmetric (http://doi.org/10.1351/goldbook.A00478).

Image: Not defined (https://goldbook.iupac.org/img/inline/P04921.png) 

Source: PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2214 (https://doi.org/10.1351/pac199668122193)

Citation: 'pseudo-asymmetric carbon atom' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04921

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