Fulminic acid

Fulminic acid is an acid with the formula HCNO, more specifically H−C≡N⁺−O⁻. It is an isomer of isocyanic acid (H−N=C=O) and of its elusive tautomer, cyanic acid (H−O−C≡N), and also of isofulminic acid (H−O−N⁺≡C⁻).^[1]

Fulminic acid

Names
IUPAC name Oxidoazaniumylidynemethane
Identifiers
CAS Number	506-85-4 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1071209
ChEBI	CHEBI:29813 Y
ChEMBL	ChEMBL185198 Y
ChemSpider	454715 Y
Gmelin Reference	772
PubChem CID	521293
CompTox Dashboard (EPA)	DTXSID30334603
InChI InChI=1S/CHNO/c1-2-3/h1H Y Key: UXKUODQYLDZXDL-UHFFFAOYSA-N Y InChI=1/CHNO/c1-2-3/h1H Key: UXKUODQYLDZXDL-UHFFFAOYAL
SMILES [O-][N+]#C
Properties
Chemical formula	HCNO
Molar mass	43.02 g mol−1
Conjugate base	Fulminate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Fulminate is the anion [C⁻≡N⁺−O⁻] of any of its salts. For historical reasons, the fulminate functional group is understood to be −O−N⁺≡C⁻ as in isofulminic acid;^[2] whereas the group −C≡N⁺O⁻ is called nitrile oxide.

History

This chemical was known since the early 1800s through its salts and via the products of reactions in which it was proposed to exist,^[3] but the acid itself was not detected until 1966.^[1]

Structure

Fulminic acid was long believed to have a structure of H–O–N⁺≡C⁻. It wasn't until the 1966 isolation and analysis of a pure sample of fulminic acid that this structural idea was conclusively disproven.^[3] The chemical that actually has that structure, isofulminic acid (a tautomer of the actual fulminic acid structure) was eventually detected in 1988.^[3]

The structure of the molecule has been determined by microwave spectroscopy with the following bond-lengths - C-H: 1.027(1) Å, C-N: 1.161(15) Å, N-O: 1.207(15) Å.^[4]

Synthesis

A convenient synthesis involves flash pyrolysis of certain oximes. In contrast to earlier syntheses, this method avoids the use of highly explosive metal fulminates.^[5]