Methylidyne radical
| Names | |
|---|---|
| Systematic IUPAC name
Hydridocarbon[1] | |
| Identifiers | |
3D model (JSmol)
|
|
| 7801830 | |
| ChEBI | |
| 24689 | |
CompTox Dashboard (EPA)
|
|
| |
| |
| Properties | |
| CH3• | |
| Molar mass | 13.0186 g mol−1 |
| Appearance | Colourless gas |
| Reacts | |
| Thermochemistry | |
Std molar
entropy (S⦵298) |
183.04 J K−1 mol−1 |
Std enthalpy of
formation (ΔfH⦵298) |
594.13 kJ mol−1 |
| Related compounds | |
Related compounds
|
Methyl (CH3) Methylene (CH2) Carbide (C) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Methylidyne (also systematically named hydridocarbon(•)), also called carbyne, is an organic compound with the chemical formula CH• (also written as [CH]).
Methylidyne is the simplest carbyne. It is a highly reactive gas, that is quickly destroyed in ordinary conditions but is abundant in the interstellar medium (and was one of the first molecules to be detected there).[2]
In October 2016, astronomers reported that the very basic chemical ingredients of life – the carbon-hydrogen molecule (CH, or methylidyne radical), the carbon-hydrogen positive ion (CH+), and the carbon ion (C+) – are the result of ultraviolet light from stars, rather than in other ways, such as the result of turbulent events related to supernovae and young stars, as thought earlier.[3] These results have given new light to the formation of organic compounds in the early development of life on earth.
Nomenclature
The trivial name carbyne is the preferred IUPAC name. The systematic names methylidyne, and hydridocarbon(•), valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively.
Methylidyne is viewed as methane with three hydrogen atoms removed. By default, this name pays no regard to the radicality of methylidyne. When the radicality is considered, the radical states with one unpaired electron are named methylylidene, whereas the radical excited states with three unpaired electrons are named methanetriyl.
Bonding
As an odd-electron species, CH is a radical. The ground state is a doublet (X2Π). The first two excited states are a quartet (with three unpaired electrons) (a4Σ−) and a doublet (A2Δ). The quartet lies at 71 kJ above the ground state.[4] Reactions of the doublet radical with non-radical species involves insertion or addition, whereas reactions of the quartet radical generally involves only abstraction.
- [CH]•(X2Π) + H
2O → [CHO]• + H
2 or [CH
2(OH)]• - [CH]3•(a4Σ−) + H
2O → [CH
2] + [HO]•
Methylidynetricobaltnonacarbonyl is an example of a metal cluster containing a methylidyne ligand.
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Occurrence and reactivity
Fischer–Tropsch intermediate
Methylidyne-like species are implied intermediates in the Fischer–Tropsch process, the hydrogenation of CO into hydrocarbons. Methylidyne entities are assumed to bond to the catalyst's surface. A hypothetical sequence is:
- MnCO + 1/2 H2 → MnCOH
- MnCOH + H2 → MnCH + H2O
A molecular example of an MnCH is HCCo
3(CO)
9.[5]
- MnCH + 1/2 H2 → MnCH2
The methylene ligand (H2C) is poised couple to CO or to another methylene, thereby growing the C–C chain.[6]
Amphotericity
The methylylidyne group can exhibit both Lewis-acidic and Lewis basic character.[7] Such behavior is only of theoretical interest since it is not possible to produce methylylidyne.
Preparation
Methylidine can be prepared from bromoform.[5]
See also
References
- ^ "hydridocarbon (CHEBI:51382)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute. IUPAC Name.
- ^ Encyclopedia of Astrobiology, Volume 1 edited by Ricardo Amils, José Cernicharo Quintanilla, Henderson James Cleaves, William M. Irvine, Daniele Pinti, Michel Viso. 2011, Springer: Heidelberg
- ^ Landau, Elizabeth (12 October 2016). "Building Blocks of Life's Building Blocks Come From Starlight". NASA. Retrieved 13 October 2016.
- ^ Brooks, Bernard R.; Schaefer III, Henry F. (1 December 1977). "Reactions of Carbynes. Potential Energy Surfaces for the Doublet and Quartet Methylidyne (CH) Reactions with Molecular Hydrogen". The Journal of Chemical Physics. 67 (11). AIP Publishing: 5146–5151. doi:10.1063/1.434743.
- ^ a b Nestle, Mara O.; Hallgren, John E.; Seyferth, Dietmar; Dawson, Peter; Robinson, Brian H. (1 January 1980). "μ3-Methylidyne and μ3-Benzylidyne-Tris(Tricarbonylcobalt)". In Busch, Daryle H. (ed.). Inorganic Syntheses, Vol. 20 (PDF). John Wiley & Sons, Inc. pp. 226–229. ISBN 9780470132517.
- ^ W. A. Herrmann "Organometallic Aspects of the Fischer-Tropsch Synthesis" Angewandte Chemie International Edition in English, 1982, Volume 21, Issue 2, pages 117–130. doi:10.1002/anie.198201171
- ^ Anderson, Stuart, M.; McCurdy, K. E.; Kolb, C. E. (February 1989). "The Methylidyne Radical + Carbon Monoxide Reaction: Rate Coefficient for Carbon Atom Exchange at 294 K". The Journal of Physical Chemistry. 93 (3). ACS Publications: 1042–1048. doi:10.1021/j100340a007.
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