Structural Isomer Definition and Examples

What Is a Structural Isomer?

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

Structural Isomer Definition

Structural isomers are isomers that have the same component atoms but 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.

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.
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Helmenstine, Anne Marie, Ph.D. "Structural Isomer Definition and Examples." ThoughtCo, Feb. 10, 2016, thoughtco.com/definition-of-structural-isomer-and-examples-605698. Helmenstine, Anne Marie, Ph.D. (2016, February 10). Structural Isomer Definition and Examples. Retrieved from https://www.thoughtco.com/definition-of-structural-isomer-and-examples-605698 Helmenstine, Anne Marie, Ph.D. "Structural Isomer Definition and Examples." ThoughtCo. https://www.thoughtco.com/definition-of-structural-isomer-and-examples-605698 (accessed January 22, 2018).