 | |||
| |||
| Names | |||
|---|---|---|---|
| Preferred IUPAC name Methylidyne[1] | |||
| Systematic IUPAC name | |||
| Identifiers | |||
3D model (JSmol) | |||
| 7801830 | |||
| ChEBI | |||
| 24689 | |||
| |||
| |||
| Properties | |||
| CH,CH•,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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Methylidyne, or (unsubstituted)carbyne, is anorganic compound whose molecule consists of a singlehydrogen atombonded to acarbon atom. It is the parent compound of thecarbynes, which can be seen as obtained from it by substitution of otherfunctional groups for the hydrogen.
The carbon atom is left with either one or three unpairedelectrons (unsatisfiedvalence bonds), depending on the molecule'sexcitation state; making it aradical. Accordingly, thechemical formula can be CH• or CH3• (also written as⫶CH); each dot representing an unpaired electron. The corresponding systematic names aremethylidyne orhydridocarbon(•), andmethanetriyl orhydridocarbon(3•). However, the formula is often written simply as CH.
Methylidyne is a highlyreactive gas, that is quickly destroyed in ordinary conditions but is abundant in theinterstellar medium (and was one of the firstmolecules to be detected there).[4]
Thetrivial namecarbyne is thepreferred IUPAC name.
Following the substitutive nomenclature, the molecule is viewed as methane with three hydrogen atoms removed, yielding the systematic name "methylidyne".
Following the additive nomenclature, the molecule is viewed as a hydrogen atom bonded to a carbon atom, yielding the name "hydridocarbon".
By default, these names pay no regard to the excitation state of the molecule. When that attribute is considered, the states with one unpaired electron are named "methylylidene" or "hydridocarbon(•)", whereas the excited states with three unpaired electrons are named "methanetriyl" or "hydridocarbon(3•)".
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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/mol above the ground state.[5]
Reactions of the doublet radical with non-radical species involves insertion or addition:
whereas reactions of the quartet radical generally involves only abstraction:
Methylidyne can bind to metal atoms astridentate ligand incoordination complexes. An example ismethylidynetricobaltnonacarbonylHCCo
3(CO)
9.[6]
Methylidyne-like species are implied intermediates in theFischer–Tropsch process, thehydrogenation of CO to producehydrocarbons. Methylidyne entities are assumed to bond to thecatalyst's surface. A hypothetical sequence is:[6]
The MnCH intermediate has a tridentate methylidine ligand. Themethylene ligand (H2C) is then poised couple to CO or to another methylene, thereby growing the C–C chain.[7]
The methylylidyne group can exhibit bothLewis acidic and Lewis basic character.[8] Such behavior is only of theoretical interest since it is not possible to produce methylidyne.
In October 2016, astronomers reported that the methylidyne radical⫶CH, the carbon-hydrogen positive ion:CH+, and the carbon ion⫶C+ are the result ofultraviolet light fromstars, rather than in other ways, such as the result of turbulent events related tosupernovas andyoung stars, as thought earlier.[9]
Methylidyne can be prepared frombromoform.[6]
