Isomerism of Cyclic Derivatives

In general, four kinds of isomerism may be encountered amongst cyclic phosphazenes  

Positional isomerism, which arises when a given substituent has a choice of P atom to which it may be attached. 

cis-trans isomerism, which arises when geometrically different forms can be obtained by placing a substituent alternatively above or below the plane of the ring when attached to the same P atom. 

Optical isomerism, which can be expected when a particular isomer cannot be superimposed on its mirror image. 

Conformational isomerism, which could arise if any of the above isomers were associated with more than one ring shape such as the boat and chair forms of (PNCl2)4. 

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