pro-R, pro-S
A @S05981@ group c (as in tetrahedral Xabc2) is described as pro-R if, when it is arbitrarily assigned @C01082@ over the other @S05981@ group c, the configuration of the thus generated @C01057@ centre is assigned the @S05976@ R. The other group c is then described as pro-S. This method for distinguishing between @S05981@ groups can be applied to other kinds of prochiral molecular entities or @P04859@ parts of molecular entities considered on their own.
prochirality centre
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2214 [Terms] [Paper]