# Chemistry - Why does N(OH)3 not exist?

## Solution 1:

Although the acid and its salts are unknown, orthonitrite esters have been found, and from a natural source at that [1]. The orthonitrite function, which is trivalent rather than monovalent as nitrate would be, is incorporated into a macrocycle that hinders its decomposition.

The picture below is from Ref. 1.

Reference:

1. Leanne Murray,* Tang K. Lim,* Graeme CurrieB and Robert J., "Aplidites (A-G): Macrocyclic Orthonitrites from an Australian Tunicate, Aplidium sp.", Aust. J. Chem., 1995, 48, 1253-1266.Link

## Solution 2:

Well let's not focus on your text but on the actual question here about $$\ce{N(OH)3}$$. I can only give you some ideas here but not a definite answer.

Whenever we have tests for our first semester students there are some who forgot what a nitrate was, or nitric acid. But as we ask for a nitrate as trivial name an ortho-nitrate is an accepted answer as well. And many people will just try to balance things with $$\ce{X(OH)_n}$$ until it fits. It's not wrong in a test but we have to think about these compounds.

Let's take silicates. There are ortho-silicates, so salts that derive from the ortho-silicic acid $$\ce{H4SiO4}$$ or $$\ce{Si(OH)4}$$. If you try to make this acid however it will start to polymerize while water is being produced. The reason for this is that you have a positively charged $$\ce{H^+}$$ that can be deprotonated easily close to an $$\ce{Si^4+}$$ center in your $$\ce{Si-OH}$$-bond. Hence two of these centers will react to something like $$\ce{Si-O-Si + H2O}$$ until something like a meta-silicic acid forms.

Now going back to our nitric acid first with $$\ce{N^{+5}}$$. We know the acid is called $$\ce{HNO3}$$. If we add a water to this we will get the ortho-nitric acid $$\ce{NO(OH)3}$$ or $$\ce{H3NO4}$$. Much as with the ortho-silicates we can find examples like the compound $$\ce{Na3NO4}$$ which could formally be the salt of the ortho-nitric acid.

Now if we want the same for nitrous acid $$\ce{HNO2}$$, well let's add water $$\ce{H3NO3}$$ or $$\ce{N(OH)3}$$. Does it exist? Well there is a salt $$\ce{Na3NO3}$$. The problem is, this is no ortho-nitrite but an oxide-nitrite $$\ce{Na3[NO2]O}$$.

I can't tell you however why there hasn't been an ortho-nitrite formed, yet. These ortho-acids are just not very stable.

## Solution 3:

The question presupposes that $$\ce{N(OH)3}$$ does not exist.

However, Ab initio molecular dynamics evidence of a new stable symmetric Cs structure for N(OH)3 Chemical Physics Letters volume 435, pages 34-38 says:

We point out that very few studies have addressed N(OH)3 and this study is relevant in the context of its possible detection in the gas phase.

See also A new non-symmetric N(OH)3 species: Comparison with the C3 species and thermochemistry at the HF, DFT, MP2, MP4 and CCSD(T) levels of theory Journal of Molecular Structure: THEOCHEM, volume 802, pages 111-115.

## Solution 4:

It isn't just nitrogen that fails to form an orthoacid with the formula $$\ce{X(OH)3}$$. The same thing happens with phosphorus. The phosphorous acid $$\ce{H3PO3}$$ is not $$\ce{P(OH)3}$$, with three equivalent $$\ce{OH}$$ groups as you might believe. This phosphorous acid has one H atom that is impossible to neutralize. Its structure is better described by $$\ce{HPO(OH)2}$$, with a central $$\ce{P}$$ atom surrounded by one $$\ce{H}$$, one $$\ce{O}$$ and two $$\ce{OH}$$ groups. Neutralized by a hydroxide it can produce two series of salts, and not three. With $$\ce{NaOH}$$, it gives: $$\ce{NaH2PO3}$$, $$\ce{Na2HPO3}$$. $$\ce{Na3PO3}$$ does not exist.

Arsenic, the next element in Group 15, does form the acid $$\ce{H3AsO3}$$ in water solution, and normal salts thereof.