Stereocenter

In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups creates a new stereoisomer.

They are defined as a location (point) within a molecule, rather than a particular atom, in which the interchanging of two groups creates a stereoisomer.

[6] Enantiomers and diastereomers are produced due to differing stereochemical configurations of molecules containing the same composition and connectivity (bonding); the molecules must have multiple (two or more) stereocenters to be classified as enantiomers or diastereomers.

[4] Since a meso compound is superposable on its mirror image, the two "stereoisomers" are actually identical.

Resultantly, a meso compound will reduce the number of stereoisomers to below the hypothetical 2n amount due to symmetry.

[6] The Cahn-Ingold-Prelog (CIP) system uses R and S designations to define the configuration of atoms about any stereocenter.

[9] Racemization by nitrogen inversion may be restricted (such as quaternary ammonium or phosphonium cations), or slow, which allows the existence of chirality.

[9] Metal atoms with tetrahedral or octahedral geometries may also be chiral due to having different ligands.

Having three bidentate ligands of only one type gives a propeller-type structure, with two different enantiomers denoted Λ and Δ.

However, there are some exceptions like meso compounds that make molecules with multiple stereocenters considered achiral.