Fulminic acid
Chemical compound (H–C≡N–O)
From Wikipedia, the free encyclopedia
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]
| |
 | |
| Names | |
|---|---|
| IUPAC name
Oxidoazaniumylidynemethane | |
| Identifiers | |
3D model (JSmol) |
|
| 1071209 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| 772 | |
PubChem CID |
|
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| 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).
| |
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
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]
A 1967 microwave spectroscopy study described fulminic acid as linear, with the following bond-lengths: C–H: 1.027(1) Å, C–N: 1.161(15) Å, N–O: 1.207(15) Å.[4] This predicted C–H bond length is unusually short, likely an artifact of the linear fit.[3]: 854 [5]: 24110 The molecule has a very low barrier to H–C–N bond angle flexion, making it difficult to ascertain whether its ground state is linear or slightly bent. It has variously been described as quasilinear[3]: 854 (minimum-energy bent but with a sufficiently low barrier to linearization that its rovibrational spectrum has characteristics similar to that of a linear molecule) and quasibent (minimum-energy linear but with a sufficiently low barrier to bending that zero-point fluctuations yield a rovibrational spectrum with characteristics similar to that of a bent molecule).[5][6] Accurately modeling its structure using quantum chemical computations has proven similarly challenging.[3]: 854
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.[7]