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Stereoisomerism, or spatial isomerism, can be defined as a form of isomerism. Here, molecules have the same molecular formula and sequence of bonded atoms, however, differ in the three-dimensional orientations of their atoms in space. When two or more two compounds co-exist having the same molecular formula but different properties, then this phenomenon is known as Isomerism. The compounds following the phenomenon of isomerism are known as isomers.
Read More: Organic Rearrangement Reactions
Key Terms: Isomerism, Stereoisomerism, Isomers, Structural Isomerism, Molecular Formula, Optical Isomerism, Geometric Isomerism
What is Stereoisomerism?
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The phenomenon in which the compounds have the same constitution and sequence of covalent bonds but differ in the relative position of their atoms or functional groups is known as stereoisomerism. The compounds that follow stereoisomerism are known as stereoisomers.
Stereoisomerism is all about the spatial arrangements of atoms. Spatial arrangements are the positions of the atoms in an organic compound. Stereoisomerism is also known as spatial isomerism. Stereoisomerism is of two types, optical isomerism, and geometric isomerism.
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What are Stereoisomers?
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Stereoisomers are the isomers that have the same composition but different orientations. Molecules that are stereoisomers of each other represent the same structural isomer. There are two types of stereoisomers: enantiomers and diastereomers. Enantiomers are stereoisomers that are mirror images.
Types of Stereoisomers
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The various types of stereoisomers are as follows:
| Atropisomerism | Atropisomers are defined as the stereoisomers formed of hindered rotation about one or more single bonds. This is observed in the case of many drugs. |
| Cis-trans isomerism | Cis-trans isomerism shares the same atoms joining to one another in the same way but have a different configuration. |
| Conformational isomerism | Conformational isomerism is the type of stereoisomerism wherein isomers can only be transformed by formally single bond rotations. This is observed in single-bonded systems like alkanes. |
| Diastereomers | Diastereomers are optically active isomers that are not enantiomers. |
| Enantiomers | An enantiomer is one of the pair of optical isomers, the structures of which are not superimposable on their mirror images. Chirality becomes the criteria here. |
Stereochemistry
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Stereochemistry is the branch of chemistry that emphasizes “the study of various spatial arrangements of atoms present in molecules.” It is described as the systematic presentation of a particular field of science and technology that requires a short preliminary excursion into history. Stereochemistry is also known as the ‘chemistry of space ‘, which is stereochemistry that deals with the spatial arrangements of groups and atoms in a molecule.
Stereoisomers
Read More: Carbocation Stability
What is Optical Isomerism?
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Optical isomers are isomers that are mirror images and cannot be superimposed on one another. These isomers are called enantiomers and the phenomenon they follow is called optical isomerism.
In optical isomerism, the enantiomers or the optical isomers have the same physical properties but the direction in which they rotate polarized light is different. Optical isomerism is very common in octahedral complexes.
What is Geometric Isomerism?
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Geometric isomers are also known as cis or trans isomers and they are the type of stereoisomers that result from a double bond or a ring structure. In geometric isomerism, the isomers are not the mirror image of each other and they include, meso compounds, cis-trans isomers, and E-Z isomers. The phenomenon is called geometric isomerism.
The most common examples of geometric isomers are cis-2-butene and trans-2-butene. Some other examples of geometric isomers are, cis-1,2-dichloroethene and trans-1,2-dichloroethene, (Z)-1,2-dichloroethene and (E)-1,2-dichloroethene.
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Things to Remember
- Organic compounds having the same molecular formula but different properties are called isomers.
- Stereoisomers have different spatial arrangements of atoms.
- Stereoisomers have the same composition but different orientations.
- Stereoisomerism is also known as spatial isomerism.
- In optical isomerism, the enantiomers or the optical isomers have the same physical properties but the direction in which they rotate polarized light is different.
- In geometric isomerism, the isomers are not the mirror image of each other.
- Optical isomers are also called enantiomers.
Previous Years’ Questions
- Strongest nucleophile is…
- The most reactive nucleophile among the following is…
- Which of the following can behave as both electrophile and nucleophile…
- The correct set of reagents for the following conversion is…
- Electrophilic reagents are…
- The reagents used in the conversion are… (DUET 2008)
- 2-butene shows geometrical isomerism due to… (NEET 2000)
- Complete combustion of 1.80g of an oxygen containing compound… [JEE Main 2021]
- Lassaigne's test for the detection of nitrogen fails in… [NEET 1994]
- Example of electrophile is… (AMUEEE 2011)
- The correct statement regarding electrophile is… (NEET 2017)
- Which of the following is an electrophile?
- Among the following the strongest nucleophile is…
Sample Questions
Ques: What is isomerism? (2 marks)
Ans: When two or more than two compounds co-exist having the same molecular formula but different properties, then this phenomenon is known as Isomerism.
Ques: What is stereoisomerism? (2 marks)
Ans: The phenomenon in which the compounds have the same constitution and sequence of covalent bonds but differ in the relative position of their atoms or functional groups, is known as stereoisomerism.
Ques: What are the two types of isomerism? (2 marks)
Ans: The two types of isomerism are:
- Structural Isomerism
- Stereoisomerism
Ques: What are stereoisomers? (2 marks)
Ans: The isomers that have the same composition but different orientations are called stereoisomers. The stereoisomers have different spatial arrangements of atoms.
Ques: What are the types of stereoisomers? (2 marks)
Ans: There are two types of stereoisomers:
- Enantiomers
- Diastereomers
Ques: What are the two types of Stereoisomerism? (2 marks)
Ans: The two types of stereoisomerism are:
- Geometrical isomerism
- Optical isomerism
Ques: What is geometric isomerism? (2 marks)
Ans: Geometric isomers are also known as cis or trans isomers and they are the type of stereoisomers that result from a double bond or a ring structure. The phenomenon is called geometric isomerism.
Ques: What is optical isomerism? (2 marks)
Ans: Optical isomers are the isomers that are mirror images and cannot be superimposed on one another. These isomers are called enantiomers and the phenomenon they follow is called optical isomerism.
Ques: Give examples of geometric isomerism. (2 marks)
Ans: The most common examples of geometric isomers are cis-2-butene and trans-2-butene. Some other examples are cis-1,2-dichloroethene and trans-1,2-dichloroethene, (Z)-1,2-dichloroethene and (E)-1,2-dichloroethene.
Ques: Illustrate some of the geometric isomers. (1 mark)
Ans: Some of the geometric isomers are meso compounds, cis-trans isomers, and E-Z isomers.
Ques: What is the other name of stereoisomerism? (1 mark)
Ans: Stereoisomerism is also known as spatial isomerism.
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