Electron Density of a POP Linkage

In this section rapid degradation will be considered unstable in water. This does not necessarily correlate to thermodynamic stability directly in the sense of a free energy change, but hopefully it will be easily read and understood. 

Triply linked PO3 groups are the most electron deficient. In P4O10 there are no charged O atoms and there are six POP linkages all of which are composed of triply 

Compound Average number of valence electrons per POP linkage 

The charge associated with any phosphate must lie between zero for P2O5 to -3 for orthophosphates. As noted, the charge of a phosphate is contributed exclusively by M2O or, in the case of acids, by H2O. Since the thermodynamic stable state is an orthophosphate with charge -3, it is not surprising that the rate of hydrolytic degradation of a condensed phosphate is a function of charge of the molecule. Pyrophosphates are the most stable because they are the most electron saturated of any condensed phosphate. 

It is recognized that we are discussing two electrical behaviors. In the case of the formal charges, as at the end of a polyphosphate molecule, there is the attraction of a positively charged hydronium ion toward this charged site. The Bronsted-Bjerrum rule is effective under this condition. It is also known that end group degrada- 

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