# What is the criteria for determining structure of a molecule?

Does the shape of the molecule depends on symmetry?

Why is the shape of dinitrogen trioxide ($\ce{N2O3}$):

(oxidation number of nitrogen atoms: +4, +2)

Instead of my proposal, which is much more symmetrical in terms of shape and oxidation number (of nitrogen atoms: +3, +3)

As seen from the case of $\ce{N2O3}$, which is unsymmetrical, then molecule of pyrophosphorus acid $\ce{(H4P2O5)}$ should be unsymmetrical too.

But the actual structure is symmetrical:

The rules we use are the result of numerous experiments over the last 150 years or so reacting one species with another and trying to make a consistent set of rules to explain things. But ultimately structural studies are needed, the definitive method is x-ray diffraction from a crystal of the material but of course this is a not always possible. In this case infra-red, Raman and NMR spectroscopies have been used as well as mass spectrometry. These methods do not give complete structures directly (bond lengths and angles as does x-ray diffraction) but allow confirmation of one structure (as topology) over another, for example $\ce{N2O}$ is NNO rather than NON. More latterly computational methods are being used to predict structure but ultimately these will have to be backed up by experiments.