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Valences for Sulfur, Phosphorus and Nitrogen

In light of the posting by Oliver Fiehn’s group (, I’ve decided to blog some compounds I’ve encountered in the lab. Using the 2nd formula from the previous blog (, for some cases the RDBE calculation will work if the correct atom valence is known.

Note: the nitrochloroform compound can be drawn more than one way and thus the observed RDBE can be either 1 or 2.


Elucidating a structure containing sulfur can be tricky sometimes. My approach is to consider the likely valences starting with S(II) first, then S(IV), and finally S(VI). If I have prior knowledge of the starting material or a derivative(s), I would start with that valence. If multiple O atoms are present in the Molecular Formula and the NMR data shows no OH groups, then I might favour starting with a S(IV) first.

TIP: The best approach is to cover all your bases to avoid missing something. I strongly recommend trying all valences for P, N and S, thus ruling out any other possible structure that might have otherwise been overlooked.