Enantiomers Stereoisomers that differ only being nonsuperimposable mirror images

Enantiomers Stereoisomers that differ only by being nonsuperimposible mirror images of each other, like left and right hands also known as Optical isomers. 

The mirror images of bromochlorofluoromethane have the same constitution. That is, the atoms are connected in the same order. But they differ in the arrangement of their atoms in space they are stereoisomers. Stereoisomers that are related as an object and its nonsuperimposable mirror image are classified as enantiomers. The word enantiomer describes a particular relationship between two objects. One cannot look at a single molecule in isolation and ask if it is an enantiomer any more than one can look at an individual human being and ask, Is that person a cousin Furthermore, just as an object has one, and only one, mirror image, a chiral molecule can have one, and only one, enantiomer. 

When molecules composed of the same constituents have the same structural formulas but differ only with respect to the spatial arrangement of certain atoms or groups of atoms, they are defined as stereoisomers. Stereoisomers can be optical isomers or geometrical isomers. Optical isomers are members of a set of stereoisomers, at least two of which are optically active or chiral geometrical isomers are members of a set of Stereoisomers that contains no optically active members. If the relationship between optical isomers is one of nonsuperimposable mirror images, the isomers are defined as enantiomers. Molecules having at least one pair of enantiomers are considered chiral. Optical isomers not related to each other as enantiomers are diastereomers. 

Optical activity is considered essential for protein chain folding and life would probably not be possible without dissymmetric molecules. Molecules lacking reflective symmetry (no plane of symmetry) are designated as dissymmetric. It should be noted that asymmetric molecules (possessing only a Cl axis element of symmetry) are a special class of dissymmetric molecules, but not all dissymmetric molecules will be asymmetric. Stereoisomers possess the same molecular bonding skeleton but differ in the absolute arrangement of the atoms in space. They are optically active and may be characterized as chiral. Stereoisomers that are related as object and nonsuperimposable mirror image are termed enantiomers. Those stereoisomers not so related are called diastereoisomers. 

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