Chemical isomer

Chemical isomers are molecules of the same chemical composition, but different molecular structure. In other words, two isomers will have the same number and type of atoms, but a different arrangement in space. Although these molecules are of the same composition, this different arrangement can result in a difference of physical and chemical properties (such as boiling point, melting point, etc).[1]

Isomers are very important for fuel choices when providing energy through combustion. Isomers of compounds burn differently, such as octane, which has 18 isomers.[2] For most applications the goal when burning a fuel is to have a stable burn, and certain isomers accomplish this better. For octane, the more linear isomers as visible in Figure 1 burn much quicker than isomers that are "branched" like in Figure 2. The branched structures allow the fuel to burn slowly and evenly, therefore they are of more desire.[2] Octane rating, which is the number visible on gas pumps, is a measure of how much iso-octane (Figure 2) is in a fuel mixture. The more iso-octane present in the mixture, the better the burn.

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  1. Compound Interest, A Bried Guide to Types of Isomerism in Organic Chemisty [Online], Available:
  2. 2.0 2.1 eHow, Importance of Isomers in Fuels [Online], Available:
  3. Wikimedia Commons [Online], Available:
  4. Wikimedia Commons [Online], Available:

Authors and Editors

Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: August 26, 2015
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