What is stereoisomerism?

What is stereoisomerism?

Stereoisomerism, also known as spatial isomerism, is a kind of isomerism in which molecules have the same chemical formula and bound atom sequence (constitution), but their atoms are oriented differently in three dimensions in space. This is in contrast to structural isomers, which have the same chemical formula but change in their bond connections or order. Molecules that are stereoisomers of one other have the same structural isomer by definition.

Now, let’s understand what is isomers and isomerism?

The phenomenon of isomerism occurs when two or more compounds have the same chemical formula but distinct chemical structures. Isomers are chemical compounds with similar chemical formulas but differ in characteristics and atom arrangement in the molecule. As a result, substances that display isomerism are referred to as isomers.

Isomers don’t always have the same chemical or physical characteristics as one another. Structural or constitutional isomerism, in which the bonds between the atoms differ, and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative locations of the atoms differ, are the two primary types of isomerism.

A hierarchy of isomeric connections exists. Two compounds may have the same constitutional isomer yet are stereoisomers of each other when examined further. Two molecules with the same stereoisomer but distinct conformational forms or isotopologues might be in various conformational forms or be separate isotopologues. The scope of the investigation is determined by the subject of research or the chemical and physical qualities that are of interest.

Stereoisomers:Stereoisomers contain the same atoms or isotopes but differ in their forms — the relative locations of those atoms in space, excluding rotations and translations.In theory, every atomic arrangement in a molecule or ion may be progressively changed to any other arrangement in an unlimited number of ways by moving each atom along an appropriate path. Changes in atom locations, on the other hand, will typically affect a molecule’s internal energy, which is controlled by the angles between bonds in each atom as well as the distances between atoms (whether they are bonded or not).

A conformational isomer is an arrangement of the atoms in a molecule or ion for which the internal energy is a local minimum; that is, an arrangement in which any small changes in the positions of the atoms increase the internal energy, resulting in forces that push the atoms back to their original positions. Changing the molecule’s structure from one energy minimum to another will need travelling through configurations with higher energy than and.That is, an energy barrier separates a conformation isomer from any other isomer: the amount of energy that must be temporarily added to the molecule’s internal energy in order to pass through all of the intermediate conformations along the “easiest” path (the one that minimizes that amount).


Two compounds are said to be enantiomers if their molecules are mirror images of each other, that cannot be made to coincide only by rotations or translations — like a left hand and a right hand. The two shapes are said to be chiral.

Bromochlorofluoromethane is a typical example. If the route rotates clockwise or counterclockwise as seen from the hydrogen atom, the two enantiomers may be identified. To switch from one shape to the other, those four atoms would have to lie in the same plane at some time, which would necessitate significantly straining or breaking their connections with the carbon atom. At normal temperature, the associated energy barrier between the two conformations is so high that there is almost no conversion between them, and they can be considered distinct configurations.

Except when interacted with chiral substances or in the presence of chiral catalysts, such as most enzymes, enantiomers behave similarly in chemical reactions. Because of this, most chiral substances’ two enantiomers have significantly distinct effects and roles in living organisms. The two enantiomers of a chiral molecule like glucose are generally recognized and treated as quite distinct entities in biochemistry and food science.The plane of polarized light that passes through a chiral substance is generally rotated by each enantiomer. For the two isomers, the rotation has the same magnitude but opposing perceptions, and may be used to identify and measure their concentration in a solution. Enantiomers were previously referred to as “optical isomers” because of this. The IUPA, however, considers this word to be unclear and discourages its use. Diastereomers are stereoisomers that are not enantiomers. Some diastereomers have chiral centers, whereas others do not.

Cis-trans isomerism

When two carbon atoms form a double bond, the remaining four bonds (if they are single) are forced to lay in the same plane, perpendicular to the bond’s orbital plane. If the two bonds on each carbon link to different atoms, there are two unique conformations that differ from one another by a 180-degree twist of one of the carbons around the double bond.

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