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When assigning the IR spectrum of hexachlorocyclotriphosphazene there are two prominent peaks (one due to the nitrogen-phosphorus bond and the other due to the phosphorus-chlorine bond).

There is one peak at 1179cm⁻¹ and another at 594cm⁻¹. I think that the peak at 1179cm⁻¹ is due to the phosphorus-nitrogen bond and the peak at 594cm⁻¹ is the phosphorus-chlorine bond.

My reasoning for this is that the phosphorus-nitrogen bond is shorter and therefore stronger thus it will have the higher stretching frequency.

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Is my reasoning correct?

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  • $\begingroup$ I highly doubt you can see P-N bond IR. It should be a very weak and complex set of bands. Very possibly both peaks are due to PCl2 fragment. Look in alkane IR spectroscopy to see how several bands appear from CH2 bridge. $\endgroup$ – permeakra Jan 20 '16 at 21:39
  • $\begingroup$ Or you can find a guy with access to package with analytic second derivitives (like Gaussian) and ask him to run IR spectrum calculation on the molecules. Granted, the methods sometimes (quite often) fails miserably, but It should give an idea at least. $\endgroup$ – permeakra Jan 20 '16 at 21:41

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