1. The @C01249@ of any @S05980-1@ @A00480@ with respect to any other stereogenic centre contained within the same molecular entity. Unlike @A00020@, relative configuration is reflection-invariant. Relative configuration, distinguishing @D01679@, may be denoted by the configurational descriptors \(R^{\text{*}}\), \(R^{\text{*}}\) (or l) and \(R^{\text{*}}\), \(S^{\text{*}}\) (or u) meaning, respectively, that the two centres have identical or opposite configurations. For molecules with more than two @A00478@ centres the prefix @R05254@- may be used in front of the name of one @E02069@ where R and S have been used. If any centres have known @A00020@ then only \(R^{\text{*}}\) and \(S^{\text{*}}\) can be used for the relative configuration.
    See also:
    α (alpha), β (beta) (Defs. 1 and 3)
  2. Two different molecules Xabcd and Xabce, may be said to have the same relative configurations if e takes the position of d in the tetrahedral arrangement of @L03518@ around X (i.e. the pyramidal fragments Xabc are superposable). By the same token the @E02069@ of Xabce may be said to have the opposite relative configuration to Xabcd. The terms may be applied to @C01057@ molecular entities with central atoms other than carbon but are limited to cases where the two related molecules differ in a single ligand.
Both definitions can be generalized to include @S05980-2@ other than @A00478@ centres.
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2217 [Terms] [Paper]