| Watchedfields | changed |
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| Verifiedrevid | 443827756 |
| Iupacname | Oxidoazaniumylidynemethane |
Fulminic acid is an acid with the formula HCNO, more specifically H\sC\tN+\sO-. It is an isomer of isocyanic acid (H\sN\dC\dO) and of its elusive tautomer, cyanic acid (H\sO\sC\tN), and also of isofulminic acid (H\sO\sN+\tC-).[1]
Fulminate is the anion [C-\tN+\sO-] of any of its salts. For historical reasons, the fulminate functional group is understood to be \sO\sN+\tC- as in isofulminic acid;[2] whereas the group \sC\tN+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]
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]
References
- ^ Beck, W. & Feldl, K. (1966). "The Structure of Fulminic Acid, HCNO". Angew. Chem. Int. Ed. Engl.. 5 (8): 722–723. doi:10.1002/anie.196607221
- ^ Wentrup, Curt; Gerecht, Bernd; Laqua, Dieter; Briehl, Horst; Winter, Hans Wilhelm; Reisenauer, Hans Peter; Winnewisser, Manfred (1981). "Organic fulminates, R-O-NC". Journal of Organic Chemistry. 46 (5): 1046–1048. doi:10.1021/jo00318a050
- ^ Kurzer, Frederick (2000). "Fulminic Acid in the History of Organic Chemistry". Journal of Chemical Education. 77 (7): 851–857. Bibcode:2000JChEd..77..851K. doi:10.1021/ed077p851
- ^ Winnewisser, Manfred & Bodenseh, Hans Karl (1967). "Mikrowellenspektrum, Struktur und l-Typ-Dublett-Aufspaltung der HCNO (Knallsäure)" [Microwave spectrum, structure, and l-type-doublet splitting of HCNO (fulminic acid)] (in German). Z. Naturforsch.. 22a (11): 1724–1737. Bibcode:1967ZNatA..22.1724W. doi:10.1515/zna-1967-1109. S2CID 96725880
- ^ Allen, Ashley M.; Olive, Laura N.; Gonzalez Franco, Patricia A.; Barua, Shiblee R.; Allen, Wesley D.; Schaefer, Henry F. (2024). "Fulminic acid: a quasibent spectacle". Physical Chemistry Chemical Physics. 26 (36): 24109–24125. doi:10.1039/d4cp02700k
- ^ Farnell, Leslie; Nobes, Ross H.; Radom, Leo (June 1982). "A theoretical consideration of the quasi-bent nature of the HCNO molecule". Journal of Molecular Spectroscopy. 93 (2): 271–280. doi:10.1016/0022-2852(82)90167-9
- ^ Wentrup, Curt; Gerecht, Bernd; Horst, Briehl (1979). "A New Synthesis of Fulminic Acid". Angew. Chem.. 18 (6): 467–468. doi:10.1002/anie.197904671