Methylidyne radical

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 CH^3• (also written as ⫶CH); each dot representing an unpaired electron. The corresponding systematic names are methylidyne 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).

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(3•)".

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.