Preferred Label : relative configuration;
IUPAC definition : 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 ligands around x (i.e.
the pyramidal fragments xabc are superposable). by the same token the enantiomer of
xabce may be said to have the opposite relative configuration to xabcd. the terms
may be applied to chiral 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 stereogenic units other than asymmetric
centres.; a (alpha), ß (beta) (1 and 3); the configuration of any stereogenic (asymmetric) centre with respect to any other
stereogenic centre contained within the same molecular entity. unlike absolute configuration,
relative configuration is reflection-invariant. relative configuration, distinguishing
diastereoisomers, may be denoted by the configurational descriptors r*, r* (or l)
and r*, s* (or u) meaning, respectively, that the two centres have identical or opposite
configurations. for molecules with more than two asymmetric centres the prefix rel-
may be used in front of the name of one enantiomer where rand s have been used. if
any centres have known absolute configuration then only r* and s* can be used for
the relative configuration.;
Origin ID : R05260;
See also
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 ligands around x (i.e.
the pyramidal fragments xabc are superposable). by the same token the enantiomer of
xabce may be said to have the opposite relative configuration to xabcd. the terms
may be applied to chiral 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 stereogenic units other than asymmetric
centres.
a (alpha), ß (beta) (1 and 3)
the configuration of any stereogenic (asymmetric) centre with respect to any other
stereogenic centre contained within the same molecular entity. unlike absolute configuration,
relative configuration is reflection-invariant. relative configuration, distinguishing
diastereoisomers, may be denoted by the configurational descriptors r*, r* (or l)
and r*, s* (or u) meaning, respectively, that the two centres have identical or opposite
configurations. for molecules with more than two asymmetric centres the prefix rel-
may be used in front of the name of one enantiomer where rand s have been used. if
any centres have known absolute configuration then only r* and s* can be used for
the relative configuration.
