What is the Difference Between Geometric Isomers and Structural Isomers?

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The main difference between geometric isomers and structural isomers lies in the arrangement of atoms in a molecule:

  • Geometric Isomers: These are compounds with the same molecular formula but different arrangements of atoms in space, often resulting from restricted rotation around a single or double bond. Geometric isomers are also known as stereoisomers. They have the same molecular formula and connectivity but different arrangements in space. For example, cis-dibromoethene and trans-dibromoethene are geometric isomers because they have the same molecular formula (C₂H₄Br₂) but different arrangements of the Br groups in space.
  • Structural Isomers: These are compounds with the same molecular formula but different arrangements of atoms in bonding. Structural isomers have different structures, meaning the way the atoms are bonded to each other is different. For example, n-butane and iso-butane are structural isomers because they have the same molecular formula (C₄H₁₀) but different arrangements of atoms in bonding.

In summary:

  • Isomers are molecules with the same molecular formula but different arrangements of atoms.
  • Geometric isomers have the same molecular formula and connectivity but different arrangements in space.
  • Structural isomers have the same molecular formula but different arrangements of atoms in bonding.

Comparative Table: Geometric Isomers vs Structural Isomers

Here is a table comparing geometric isomers and structural isomers:

Property Geometric Isomers Structural Isomers
Definition Geometric isomers are stereoisomers with the same molecular formula and connectivity but different arrangements in space. Structural isomers have different connectivity and differ in the arrangement of atoms.
Also known as Cis-trans isomers. Skeletal, positional, and functional group isomers.
Formation Geometric isomers are formed when a double bond in an alkene is not free to rotate due to the nature of the bond. Structural isomers are formed by hydrocarbons with a minimum of four carbon atoms and can be classified into skeletal, positional, and functional group isomers.
Examples Cis-but-2-ene and trans-but-2-ene. Isomers with the same molecular formula but different arrangements of atoms, such as butane and isobutane.

In summary, geometric isomers have the same molecular formula and connectivity but differ in their spatial arrangements, while structural isomers have different connectivity and differ in the arrangement of atoms.