What is the Difference Between Constitutional Isomers and Stereoisomers?

06/02/2025 • Giovanni Medeiros

The main difference between constitutional isomers and stereoisomers lies in the arrangement of atoms in the molecule and their bonding relationships. Here is a comparison of the two types of isomers:

Constitutional Isomers:

  • Have the same molecular formula but a different bonding arrangement among the atoms.
  • Differ in the way their atoms are connected.
  • Have different connectivities, which can be identified through nomenclature or by examining the structure of the molecule.

Stereoisomers:

  • Have identical molecular formulas and arrangements of atoms.
  • Differ only in the spatial orientation of groups in the molecule.
  • Include several types, such as enantiomers, diastereomers, geometric isomers, and conformers.

Stereoisomers can be further classified into different types:

  1. Enantiomers: Pairs of molecules that are mirror images of each other but cannot be superimposed on each other. They have the same physical properties, but their optical properties are opposite.
  2. Diastereomers: Stereoisomers that are not mirror images of each other. They have different physical and optical properties.
  3. Geometric Isomers: Stereoisomers resulting from the restriction of rotation around a carbon-carbon double bond.
  4. Conformers: Stereoisomers that show the same compound with different carbon-carbon bond angles, but without any restriction of rotation around a carbon-carbon double bond.

In summary, constitutional isomers differ in the way their atoms are connected, while stereoisomers differ in their spatial arrangement.

Comparative Table: Constitutional Isomers vs Stereoisomers

Here is a table comparing the differences between constitutional isomers and stereoisomers:

Feature Constitutional Isomers Stereoisomers
Definition Compounds with the same molecular formula but different bonding arrangements among atoms. Compounds with the same molecular formula and arrangement of atoms, differing only in the spatial orientation of groups in the molecule.
Types Skeletal, positional, and functional group isomers. Enantiomers, diastereomers, cis-trans isomers, conformational isomers, etc.
Arrangement of Atoms Different arrangement of atoms. Same arrangement of atoms.
Chirality Chirality is absent. Chirality is present.
Chemical Names Can have very different chemical names. Usually have the same chemical name with a letter or symbol indicating the difference in spatial arrangement.
Physical Properties Differ more rapidly than between stereoisomers. Differ less than between constitutional isomers.

In summary, constitutional isomers differ in the way their atoms are connected, while stereoisomers differ in their spatial arrangement.

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