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Chapter 3:
Conformations of Alkanes and Cycloalkanes 
Ch 3 contents

Polycyclic Systems

    Both nature and mankind has created many examples of compounds that contain more than one ring system. 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 shown below.
 

Cubane 
Adamantane 
Question : Can recognise which class each belongs to ? 

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© Dr. Ian Hunt, Department of Chemistry University of Calgary