Methylidyne, or (unsubstituted) carbyne, is an organic compound whose molecule consists of a single hydrogen atom bonded to a carbon atom. It is the parent compound of the carbynes, which can be seen as obtained from it by substitution of other functional groups for the hydrogen.
The carbon atom is left with either one or three unpaired electrons (unsatisfied valence bonds), depending on the molecule's excitation state; making it a radical. Accordingly, the chemical formula can be CH• or CH3• (also written as ⫶CH); each dot representing an unpaired electron. The corresponding systematic names are methylylidene or hydridocarbon(•), and methanetriyl or hydridocarbon(3•). However, the formula is often written simply as CH.
Methylidyne 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).[4]
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•)".
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/mol above the ground state.[5]
Reactions of the doublet radical with non-radical species involves insertion or addition:
[CH]•(X2Π) + H 2O → H• + CH 2O (major) or [CH 2(OH)]•
whereas reactions of the quartet radical generally involves only abstraction:
The MnCH intermediate has a tridentate methylidine ligand. The methylene ligand (H2C) is then poised couple to CO or to another methylene, thereby growing the C–C chain.[7]
Amphotericity
The methylylidyne group can exhibit both Lewis acidic and Lewis basic character.[8] Such behavior is only of theoretical interest since it is not possible to produce methylidyne.
In interstellar space
In October 2016, astronomers reported that the methylidyne radical ⫶CH, 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 supernovas and young stars, as thought earlier.[9]
Henri A. Favre; Warren H. Powell (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Cambridge, England: Royal Society of Chemistry. p.1054. ISBN978-0-85404-182-4.
"hydridocarbon(3•)". Substance page at the Chemical Entities of Biological Interest (ChEBI) website, European Bioinformatics Institute, UK. Accessed on 2019-04-20
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
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): 5146–5151. Bibcode:1977JChPh..67.5146B. doi:10.1063/1.434743.
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): 1042–1048. doi:10.1021/j100340a007.
This article uses material from the Wikipedia article Methylidyne_radical, and is written by contributors.
Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.