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Chapter 3: Conformations of Alkanes and Cycloalkanes 
Ch 3 contents

Polycyclic Systems

Both nature and human kind 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 atom common to two rings, then the system is said to be "spirocyclic" and the central atom 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. 


A couple of interesting examples are shown below.





QUESTION : Can recognise which class each belongs to ? ANSWER

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