Isomer

"Molecules that are not identical to their mirror images are kinds of stereoisomers called enantiomers (Greek enantio, meaning “opposite”). Enantiomers are related to each other as a right hand is related to a left hand and result whenever a tetrahedral carbon is bonded to four different substituents (one need not be H)."

"Note carefully the difference between enantiomers and diastereomers: enantiomers have opposite configurations at all chirality centers, whereas diastereomers have opposite configurations at some (one or more) chirality centers but the same configuration at others."

"When chemists make chiral compounds—molecules that behave like object and mirror image, such as amino acids, sugars, drugs, or nucleic acids—they like to use asymmetric catalysis, in which a chiral catalyst selectively accelerates the reaction that leads to one mirror-image isomer, also called enantiomer."

"If we were to isolate each enantiomer in pure form, we would find that we could not distinguish between them on the basis of their physical properties, such as boiling points, melting points, and densities. This result should not surprise us: Their bonds are identical and so are their energy contents. However, when a special kind of light, called plane-polarized light, is passed through a sample of one of the enantiomers, the plane of polarization of the incoming light is rotatedin one direction (either clockwise or counterclockwise). When the same experiment is repeated with the other enantiomer, the plane of the polarized light is rotated by exactly the same amount but in the opposite direction."

"In contrast with enantiomers, diastereomers, because they are not mirror images of each other, are molecules with different physical and chemical properties."