Is HC(=NH)OH a stable compound?

The molecule $\ce{HC(=NH)OH}$ has been shown to derive from hydrogen cyanide and water (compound **7**). Is it a stable compound?


[![enter image description here](https://i.stack.imgur.com/9KkYT.png)](https://i.stack.imgur.com/9KkYT.png)


source: Das, T.; Ghule, S.; Vanka, K. Insights Into the Origin of Life: Did It Begin from $\ce{HCN}$ and $\ce{H\_2O}$? *ACS Cent. Sci.* **2019**, *5*, 1532–1540. <https://doi.org/10.1021/acscentsci.9b00520> (open access).




You are considering the following molecule.


[![formimidic acid structure and name](https://i.stack.imgur.com/7bDkf.png)](https://i.stack.imgur.com/7bDkf.png)


As stated in the referenced study:



> 
> Values have been calculated at the B3LYP-D3/TZVP+COSMO(ε =
> 80.0)//RI-CC2/TZVP+COSMO(ε = 80.0) and the B3LYP-D3/TZVP+ COSMO(ε = 80.0)//RIMP2/TZVP+COSMO(ε = 80.0) (values shown in parentheses) levels of theory in kcal/mol.
> 
> 
> 


Regarding the accuracy of calculations, Becke, A.D.$^1$ (2014) says, "with dispersion interactions in place, the future looks bright," albeit with warnings "we cannot, quite yet forget the basics," "DFT heaven is probably unattainable," and "DFAs, local or nonlocal, will never be exact," and ends with the note "The next fifty (forty-three) years will be as interesting as the first."


However, the study (referred in the question) suggests that many compounds in the suggested mechanism have been observed experimentally:



> 
> The use of the nanoreactor produces as an output many different
> pathways to new species from the starting reactants. In most of the
> pathways, formaldehyde **3**, urea **26**, formaldimine **2**, and
> glycolonitrile **4** were seen to be formed as intermediates. This
> suggests that these species were the key intermediates en route to the
> formation of the target molecules, as has also been noted by
> experimentalists.
> 
> 
> 


Quick (and *even less accurate*) calculations using [MolCalc](https://molcalc.org/) shows $\Delta\_f H = \mathrm{-122.76 kJ mol^{-1}}$, a negative value, suggesting it is a (somewhat) stable molecule.


$$
\ce{C(s) + \dfrac{3}{2}H2(g) + \dfrac{1}{2}N\_2(g) \xrightarrow{\Delta H \approx -122.76 \mathrm{kJ\ mol^{-1}}} HOCH=NH}
$$


However, I couldn't find any results for "synthesis of formimidic acid" and thus it could be a (somewhat unstable) intermediate. As has been pointed out in other answers, the tautomer (formamide) is more stable\*.


[![formimidic acid formamide equilibrium favoring formamide formation](https://i.stack.imgur.com/vkvKK.png)](https://i.stack.imgur.com/vkvKK.png)


\*Approximate heats of formation calculated using [MolCalc](https://molcalc.org/).


### References


1. Axel D. Becke; Perspective: Fifty years of density-functional theory in chemical physics. J. Chem. Phys. 14 May 2014; 140 (18): 18A301. [10.1063/1.4869598](https://doi.org/10.1063/1.4869598)


 5

Compound **7** is the imidic acid of formic acid (hence *formimidic acid*). However as indicated by $\Delta{}G$, its tautomer formamide **8** is thermodynamically favoured. Some activation ($\Delta{}G^\#$) has to be invested, though.


 4