Term: pro-R, pro-S
https://doi.org/10.1351/goldbook.P04889

Definition:
A stereoheterotopic group c (as in tetrahedral Xabc2) is described as pro-R if, when it is arbitrarily assigned CIP priority over the other stereoheterotopic group c, the configuration of the thus generated chiral centre is assigned the stereodescriptor R. The other group c is then described as pro-S. This method for distinguishing between stereoheterotopic groups can be applied to other kinds of prochiral molecular entities or prochiral parts of molecular entities considered on their own.

Related Terms:
1) stereoheterotopic (http://doi.org/10.1351/goldbook.S05981).
2) cip priority (http://doi.org/10.1351/goldbook.C01082).
3) stereodescriptor (http://doi.org/10.1351/goldbook.S05976).
4) prochiral (http://doi.org/10.1351/goldbook.P04859).
5) chiral (http://doi.org/10.1351/goldbook.C01057).
6) prochirality centre (http://doi.org/10.1351/goldbook.P04860).

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

Citation: '<i>pro-R, pro-S</i>' 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.P04889

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