Isomerism polytopal

In principle this type of isomerism (also known as polytopal isomerism) is possible with any coordination number for which there is more than one known stereochemistry. However, to actually occur the isomers need to be of comparable stability, and to be separable there... 

Permutational isomerization, i.e., the interconversion of permutational isomers, is the redistribution of ligands on any polytopal framework. This redistribution can take place by two different processes ... 

The regular permutational isomerizations (or regular polytopal rearrangements) take place without the rupture of bonds, i.e., with preservation of neighborhood relationships. 

The irregular permutational isomerizations (or irregular polytopal rearrangements) occur with fission and re-formation of bonds. 

When a 1,2-diol reacts with DTPP, the replacement of two equivalents of ethanol by bis(transoxyphosphoranylation) of the diol is rapid at ambient temperature affording dioxaphosphoranes B (79). Assuming that Berry polytopal isomerization of dioxaphosphoranes B as well as equilibration with the regioisomeric oxyphosphonium betaines C are also facile (79), the chain closure to the cyclic ether by intramolecular displacement (i.e., 3-exo-tet) 20) of TPPO from betaines C is expected to be ratelimiting (Scheme 1). 

A general graphical topological approach to representing intramolecular processes of trigonal-bipyramidal molecules has been presented, and these processes have been used to illustrate a general topological treatment of polytopal isomerizations. ... 

Among new concepts that have been put forward are the relationships between symmetry, topology, and aromaticity, and bond stretch isomerism and polytopal rearrangements. ... 

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