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What is Stereochemistry in Chemistry?

Stereochemistry is defined as the branch of chemistry which involves “the study of various spatial arrangements of atoms present in molecules”.

Stereochemistry is described as the systematic presentation of a particular field of science and technology traditionally requires a short preliminary excursion into history. Stereochemistry is also said as the ‘chemistry of space ‘, which is stereochemistry that deals with the spatial arrangements of groups and atoms in a molecule.


More about Stereochemistry

Stereochemistry is capable of tracing its roots to 1842 when the French chemist, named, Louis Pasteur made an observation, which the salts of tartaric acid collected from a vessel of wine production which has the ability to rotate plane-polarized light, whereas similar salts from various sources did not hold this ability. This whole phenomenon is explained by the optical isomerism.


Types of Stereoisomers

Different types of stereoisomers are tabulated below. Let us discuss more about them.

Atropisomerism

Atropisomerism is the property of any molecule or an object of being non-superimposable on its mirror image.


Cis-trans isomerism

Cis-trans isomerism shares the same atoms which are joined to one another in the same way but have a different configuration.

Conformational isomerism

Conformational isomerism is a type of stereoisomerism in which isomers can only be converted by formally single bond rotations.

Diastereomers 

Diastereomers are more optically active in the isomers, which are not enantiomers.

Enantiomers

An enantiomer is given as one of a pair of optical isomers, which are the structures, they are not superimposable on their mirror images.


Stereoisomerism

Stereoisomerism is known as “the isomerism, which is caused by the non-similar arrangements of functional groups or atoms that belong to an atom in space”. These kinds of isomers contain similar constitutions, but various geometric arrangements of atoms. Stereoisomers are broadly classified into two types, which are enantiomers and diastereomers.


  1. Enantiomers

  • When two isomers are explained as the mirror images of each other, such type of isomerism is known as enantiomerism, and these types of isomers are called enantiomers.

  • Enantiomers are the isolable and stable compounds that vary in their spatial arrangements in the 3-D space.

  • Generally, they exist as discrete pairs.

  • The properties of enantiomers are identical. However, their interaction with any plane of the polarized light can differ.

  • The direction, towards which they rotate the plane-polarized light is much different, it means, if one rotates in the right direction, the other rotates towards the left direction.


  1. Diastereomers

  • When any two isomers are not behaving as mirror images of each other, they are referred to as diastereomers.

  • A molecule with an ‘n’ number of asymmetric carbon atoms can have up to ‘2n’ diastereomers.

  • When two diastereomers vary at only one stereocenter, they are called epimers.

  • These isomers change in both physical properties and chemical reactivity.

  • A representation of enantiomers which are mirror images of each other is given below.

(image to be added soon)


Importance of Stereochemistry - Thalidomide Disaster

  • The atoms arrangement in three-dimensional space plays a major part in the molecule properties.

  • An example of the stereochemistry significance is observed in the thalidomide disaster which struck Germany in 1957.

  • This drug thalidomide was sold in the form of an over-the-counter drug, where it was initially intended to combat nausea. It can also be used by pregnant women to alleviate morning sickness.

  • However, it was discovered that this drug underwent racemization and was produced as an enantiomers mixture in the human body because of the metabolism process.

  • One of these enantiomers can be believed to cause some genetic damage in the development of embryos and lead to baby birth defects.

  • This is based on the data that over 5000 babies were born with the deformed limbs shortly after thalidomide sold commercially as an over-the-counter drug.

  • This unforeseen effect of the drug has led to the imposition of stricter drug regulation laws (only 40 per cent of the born babies with these deformities survived).

  • This disaster signifies stereochemistry importance.


Facts about Stereochemistry

  • The structure of the molecule can change according to the three-dimensional arrangement of the atoms that constitute this. Also, Stereochemistry deals with the atom’s arrangement manipulation.

  • Commonly, this branch of chemistry can be referred to as 3-D chemistry because it focuses on the stereoisomers (which are the chemical compounds with similar chemical formulas but with a different spatial arrangement in these three dimensions).

  • A branch of stereochemistry deals with the molecule’s study that exhibits chirality, which is a property of the geometry of molecules that makes them non-superimposable on their mirror images.

  • Another branch of the three-dimensional chemistry, which is called dynamic stereochemistry, involves the study of the effects of various spatial arrangements of the atoms, present in a molecule on the rate of a chemical reaction.


Stereochemistry and Regiochemistry

The arrangement of stereoisomers can be described by stereochemistry. The key distinction between stereochemistry and regiochemistry is, the final result’s atomic structure of a chemical reaction can be represented using regiochemistry, whereas stereochemistry describes the atomic arrangement and the modification of these molecules.


FAQ (Frequently Asked Questions)

1. Give the difference between enantiomers and diastereomers?

Enantiomers have non-superimposable mirror images and chiral centres. They also come in pairs only. These chiral centres, which are found in the diastereomers, are non-superimposable but they do NOT mirror images. Based on the number of stereo centres, there can be as many as more than 2.

2. Explain about chirality?

Chirality is defined as an important property of asymmetry in several branches of science. The term chirality has derived from a common chiral entity, which is the Greek “side”. If it is distinguishable from its mirror image, a system or entity is chiral; that is to say, it cannot be superimposed over it.

3. Are racemic mixtures said to be optically active?

A racemic mixture exhibits zero optical behaviour since the enantiomers contain opposite and equal unique rotations. Thus, using the polarimetry alone, it is quite difficult to explain a racemic mixture apart from the achiral material. Also, the chiral molecules hold a racemic mixture, but it contains no net optical activity.

4. What is Superposable?

Superimposable is explained as the ability to position an object over any other object, usually in a way that all the objects are visible. Often, it is interchanged with a wider superposable concept (which is the right to position an object over the other object; without any limitation of visibility).

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