Difference Between Constitutional Isomers and Stereoisomerism (With Table)

Isomers are the organic chemistry phenomenon that has two or more compounds along with the same quantitative and qualitative composition; instead; it has different biological, chemical, and physical properties. The various properties occur because of the constitution or stereoisomerism of the organic molecules.

Constitutional Isomers vs Stereoisomerism

The difference between constitutional isomers and stereoisomers is that the constitutional isomers have the same molecular formula but different bonding arrangements in the atoms. Stereoisomerism has similar molecular formulas and also in the arrangement of atoms. Both are different from each other, only in the spatial orientation of the group in the molecules.

Constitutional isomers are also known as structural isomers. It is a form of isomers where molecules with the same molecules’ properties create a bond in different orders to oppose stereoisomerism. It is a compound that has the same molecular formula yet has a different structural formula.

Stereoisomers can also be known as spatial isomers. It has quantitative, qualitative, and functional structures rather than have a different spatial orientation of molecules or their parts. The reason spatial isomers are different because they have different spatial symmetry of molecules.

Comparison Between Constitutional Isomers and Stereoisomers

Parameter of ComparisonConstitutional isomers Stereoisomers
Meaning Constitute isomers have a different structure but the same molecular formula.Stereoisomers are the same molecular functional and formula structure with different spatial orientations of molecules.
Types 
Chirality In constitutional isomers, chirality is absentIn stereoisomers, chirality is present.
Arrangement In constitutional isomers, the arrangement of an atom is different.In stereoisomers, the arrangement of an atom is the same.
Properties In constitutional isomers, molecules’ properties are different from each other.In stereoisomers, the properties of the molecules are mainly similar.

What are the Constitutional Isomers?

Constitutional isomers are known as structural isomers. It is a compound with a different structure but has the same molecular formula. There are different types of constitutional or structural isomers, just like functional group isomers, position isomers, and skeletal isomers. Skeletal isomers have different physical properties. It has uniform qualitative, quantitative and functional composition rather than it have a different chain of molecules. This chain can also be different or straight branched.

The positional isomers have different locations of the substituent, complex bond, or functional group in the chain. The positional isomers have different physical properties, and some of them also are biochemical ones. Metamerism is generally known as the form of positional isomers. 

The isomers with the same qualitative and same quantitative but different functional groups are known as functional isomers. If there is a difference in function group, this will also lead to their different chemical properties. Some good examples of functional isomers are fructose and glucose. It is also believed that functional isomers have different biochemical importance.

Another main type of structural isomerism is tautomerism, where under some conditions, some spatial structure can be translated into another alongside dynamic equilibrium between them. This isomer can also be known as the form of functional isomers.

What are Stereoisomerism?

Stereoisomers can also be known as spatial isomers. It has quantitative, qualitative, and functional structures rather than have a different spatial orientation of molecules or their parts. The reason spatial isomers are different because they have different spatial symmetry of molecules. Some main elements of symmetry are axis, plane, and center.

The stereoisomers can also be geometric, optical, conformational isomers, and configurational isomers. Geometric isomers have a different spatial arrangement of substituents relative to the symmetry plane. Geometric isometry has the possibility of a substitute group in which one side is a double bond plane, non-aromatic cycle, or Na different side. The isomers with two identical substituents on one side of the plane are known as cis-isomer, and another side of the plane is known as trans-isomer.

It is to be believed that in optical isomers, the molecules have no axis, no center, and no plane of symmetry. Optical isomers have the asymmetric type of molecules. The optical isomers are also known as enantiomers, whose biological meaning is different. Optical isomers have the same chemical properties, but they only have different optical activity.

Spatial isomerism is an isomer with the same configuration; instead, they have different spatial orientations because it is known as conformational. The different isomers result in breakage of bond and the rotation of different types of the molecule over the axis of a simple sigma bond and the displacement of the substituents. If the resulting isomers have different conformations, they are known as conformers.

Main Differences Between Constitutional Isomers and Stereoisomers

  1. Both the term constitutional and stereoisomers are different from each other, only in the group’s spatial orientation in the molecules.
  2. A constitutional isomer is a compound with different structural formulas. On the other hand, stereoisomers are the same molecular functional and formula structure with different molecules’ spatial orientations.
  3. The constitutional or structural isomers can be positional, functional, skeletal group isomers. On the other hand, stereoisomers have been configurational( optical, geometric) and conformational isomers.
  4. The constitutional or structural isomers generally have different properties. On the other hand, stereoisomers generally have similar properties.
  5. Constitutional isomers mainly have a different chemical name. On the other hand, stereoisomers have mainly the same chemical name with the same letter or symbol in front of the name to identify the orientation.
  6. In constitutional isomers, arrangements of an atom are mainly the same. On the other hand, stereoisomers have the same arrangement of the atom.
  7. In constitutional isomers, chirality is absent. On the other hand, in stereoisomers, chirality is present.

Conclusion

 As the primary difference between the term constitutional isomers and spatial isomers has been classified, it will help understand how they are different. Both terms have their types, and they are very much different from each other.

As constitutional isomers, molecules have very much different properties from each other. On the other hand, stereoisomerism molecules have similar properties. This type of small difference is there between the terms.

References

  1. https://pubs.acs.org/doi/abs/10.1021/ci9502663
  2. https://www.chinesechemsoc.org/doi/abs/10.31635/ccschem.020.201900094
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