# Why is the structure of HNO3 have a central atom rather than being linear?

Why is the structure of $$\ce{HNO3}$$ have a central atom rather than being linear?

I know formal charges need to be reduced as much as possible, and if there was a structure with two oxygens and a hydrogen dangling off the nitrogen on one side and with a double bonded oxygen on the other, wouldn't that make all atoms in it have a formal charge of $$0$$ while obeying all the rules?

To clarify, the order is hydrogen, single bond, oxygen, single bond, oxygen, single bond, nitrogen, double bond, and the last oxygen.

What you describe is not nitric acid $$\ce{HONO2}$$, but it's much less stable existing structural isomer $$\ce{HOONO}$$. From Wikipedia:

Peroxynitrous acid $$(\ce{HNO3})$$ is a reactive nitrogen species (RNS). It is the conjugate acid of peroxynitrite $$(\ce{ONOO−}).$$ It has a $$\mathrm{p}K_\mathrm{a}$$ of $$\sim 6.8.$$ It is formed in vivo from the diffusion-controlled reaction of nitrogen monoxide $$(\ce{ON^.})$$ and superoxide $$(\ce{O2^{.−}}).$$ It isomerises with a rate constant of $$k = \pu{1.2 s−1},$$ a process whereby up to $$5\%$$ of hydroxyl and nitrogen dioxide radicals may be formed. It oxidises and nitrates aromatic compounds in low yield. The mechanism may involve a complex between the aromatic compound and $$\ce{ONOOH},$$ and a transition from the cis- to the trans-configuration of $$\ce{ONOOH}.$$ Peroxynitrous acid is also important in atmospheric chemistry.

• "Formed in vivo"... Surely they meant in situ – electronpusher Jun 13 '19 at 7:28
• > A potent oxidant synthesized by the cell during its normal metabolism. Peroxynitrite is formed from the reaction of two free radicals, NITRIC OXIDE and the superoxide anion (SUPEROXIDES). pubchem.ncbi.nlm.nih – Poutnik Jun 13 '19 at 7:40
• @electronpusher No, in vivo, see other comment and this reference: ncbi.nlm.nih.gov/pubmed/15647782 – Karsten Theis Jun 13 '19 at 14:27
• Tech detail: please note that copy-pasted text (also from Wikipedia) lacks most of the intended formatting and markup features. Whenever possible, those need to be recreated manually with MathJax and Markdown (see my edit). – andselisk Jun 14 '19 at 6:33
• I do not dispute this particular case now, as I should have copied the source code instead of displayed code, to reproduce the Wikipedia look, or to reformat the displayed text copy. I do agree in this with you and I do thank you for the correction. – Poutnik Jun 14 '19 at 7:46

As discussed, there is nothing in principle to stop HNO3 having the structure you have proposed. However, it is also shown that the common anion derived from this has all oxygens equivalent (see e.g. crystal structures, or NMR studies) so that the structure like a fidget-bit is more common.

How exactly linear.First of all atoms inside the atom must be share as many electrons as their electron configuration "tells "them to share(Oxygen must share 2 electrons).Another issue is that nitrogen and oxygen have lone pairs of electrons at their valence orbital and those lone pairs repel the bonding pairs which gives the molecule its shape.

• If you're disagreeing with the possibility of existence of a linear isomer, what about the literature quoted by Poutnik? Please further elaborate your stance. – William R. Ebenezer Jun 13 '19 at 14:52
• Nitrogen makes 5 bonding pairs in HNO3 . Those 5 bonding pairs repel one another forcing the creatipn of non-linear molecule.Also oxygen has two lone pairs , which repel the bonding pairs of the oxygen , creating a non-linear molecule. – 4HonorNDFame Jun 13 '19 at 15:02
• I'm sorry, I don't quite understand your argument. Which structure are you referring to? The typical structure or the peroxo one? – William R. Ebenezer Jun 13 '19 at 15:06
• HNO3 molecule OONOH – 4HonorNDFame Jun 13 '19 at 15:08
• What do you mean general chemistry.There is no such thing as general chemistry. – 4HonorNDFame Jun 13 '19 at 18:27