In chemistry,<unk> s (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as one's left and right hands are "the same" but opposite.<unk> s have, when present in a symmetric environment, identical chemical and physical properties except for their ability to rotate plane-polarized light by equal amounts but in opposite directions. A mixture of equal parts of an optically active isomer and its<unk>  is termed racemic and has a net rotation of plane-polarized light of zero.
Two symmetrical<unk> s often do have different chemical properties related to other substances that are also<unk> s. Since many molecules in the bodies of living beings are<unk> s themselves, there is often a marked difference in the effects of two symmetrical<unk> s on living beings, including human beings.
Enantiomer
Isomer
Molecular mass
Nuclear isomer
Isotopomers
Chemical symbol
Gas constant
Fluency