Methylidyne radical
Methylidyne, or 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, depending on the molecule's excitation state; making it a radical. Accordingly, the chemical formula can be CH• or CH3• ; each dot representing an unpaired electron. The corresponding systematic names are methylidyne or hydridocarbon, and methanetriyl or hydridocarbon. However, the formula is often written simply as CH.
Methylidyne is a highly reactive gas that is quickly destroyed in ordinary conditions on Earth but is abundant in the interstellar medium.
Nomenclature
The trivial name carbyne is the preferred 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".
Bonding
As an odd-electron species, CH is a radical. The ground state is a doublet. The first two excited states are a quartet and a doublet. The quartet lies at 71 kJ/mol above the ground state.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 as tridentate ligand in coordination complexes. An example is methylidynetricobaltnonacarbonyl.
Occurrence and reactivity
Fischer–Tropsch intermediate
Methylidyne-like species are implied intermediates in the Fischer–Tropsch process, the hydrogenation of CO to produce hydrocarbons. Methylidyne entities are assumed to bond to the catalyst's surface. A hypothetical sequence is:The MnCH intermediate has a tridentate methylidine ligand. The methylene ligand is then poised couple to CO or to another methylene, thereby growing the C–C chain.