Structural Isomer Definition and Examples

Structural isomers example
These are two structural isomers of dioxin. The atoms are the same, but they are ordered differently. Todd Helmenstine

Structural isomers are isomers that have the same component atoms but they are arranged differently from each other. Structural isomerism is also known as constitutional isomerism. Contrast this with stereoisomerism, where isomers have the same atoms in the same order and with the same bonds, but oriented differently in three-dimensional space.

Key Takeaways: Structural or Constitutional Isomerism

  1. Structural or constitutional isomers share the same chemical formulas, but their atoms are arranged differently.
  2. The three types of structural isomers are skeletal isomers, positional isomers, and functional group isomers.
  3. Structural isomers differ from stereoisomers, which share the same chemical formulas and same order of atoms, but have different three-dimensional configurations.

Types of Structural Isomers

There are three categories of structural isomers:

  • Skeletal isomerism (also called chain isomerism) - structural isomers in which components of the skeleton are arranged in a different order. This is most commonly seen when the skeleton or backbone consists of a carbon chain.
  • Position isomerism (also called regioisomerism) - constitutional isomers in which a functional group or substituent changes position on a parent structure.
  • Functional group isomerism - structural isomers with the same molecular formula, but with atoms connected differently so dissimilar functional groups are formed.

Structural Isomer Examples

  1. Butane and isobutane (C4H10) are structural isomers of each other.
  2. Pentan-1-ol, pentan-2-ol, and pentan-3-ol are structural isomers that exhibit position isomerism.
  3. Cyclohexane and hex-1-ene are examples of functional group structural isomers.

Sources

  • Poppe, Laszlo; Nagy, Jozsef; Hornyanszky, Gabor; Boros, Zoltan; Mihaly, Nogradi (2016). Stereochemistry and Stereoselective Synthesis: An Introduction. Weinheim, Germany: Wiley-VCH. pp. 26–27. ISBN 978-3-527-33901-3.