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Polycyclic Molecules

Article ID: 127
Last updated: 12 Feb, 2012
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Both natural and man-made examples of compounds that contain more than one ring system are known. These can be classified depending on how many rings are present and how the rings are joined together. 

If there is a single carbon atom common to two rings, then the system is said to be "spirocyclic" and the carbon can be described as the "spirocenter". The simplest example is spiropentane.

If two or more atoms are shared between more than one ring then the system is said to be "polycyclic" in general terms or as bicyclic, tricyclic, tetracyclic etc. depending on how many rings systems are present.  The simplest polycyclic system is bicyclobutane.  
When there are two common atoms in the rings, then it is a "fused" system, as in bicyclobutane. 

If there are more than two common atoms then the a "bridged" system is obtained, the simplest example being bicyclo[1.1.1]pentane.

Some interesting examples are provided below. See if you can recognize which class they would belong to. 


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