In chemistry a stereogenic center is often mistaken for a chiral center. First, centers are never chiral, molecules are chiral. Second, a stereogenic center of a molecule produces stereoisomerism. If switching opposing ligands gives a different conformation, then the center is stereogenic. The molecule, however, does not have to be a chiral molecule, i.e., a molecule with a mirror image that is a different conformation from the original. It can be a diastereomer. Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. ... Diastereomers are stereoisomers that are not enantiomers, or mirror images of each other. ...
Diastereoisomers may be recognized because they are connected identically, they have two (or more) stereogenic atoms and comparison of those atoms reveals that the relationship at one (or more) atom is identical and the relationship at the other (or more) atom is mirror-image.
Since the diastereoisomer we made by changing the top stereogenic carbon of our original compound is not superimposable upon its mirror image, it too is optically active and has a mirror image enantiomer.
The four atoms or groups attached to the top stereogenic carbon are the same as those attached to the bottom stereogenic carbon.
Chirality in molecules incorporating a stereogenic center can be fully explained using the regular tetrahedron as a model.
Analysis of chirality in molecules incorporating a stereogenic axis, on the other hand, requires the use of a less regular, “stretched” or “extended”, tetrahedron.
Molecules incorporating a stereogenic center have a single chiral topology in which all four substituents are necessarily different.
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