In organic chemistry, a carbyne is a general term for any compound whose structure consists of an electrically neutral carbon atom connected by a single covalent bond and has three non-bonded electrons. The carbon atom has either one or three unpaired electrons, depending on its excitation state; making it a radical. The chemical formula can be written R-Co or R-C3o (also written as ?C-R), or just CH.
Carbyne molecules are generally found to be in electronic doublet states: the non-bonding electrons on carbon are arranged as one radical (unpaired electron) and one electron pair, leaving a vacant atomic orbital, rather than being a tri-radical (the quartet state). The simplest case is the CH radical, which has an electron configuration 1?2 2?2 3?2 1?. Here the 1? molecular orbital is essentially the carbon 1s atomic orbital, and the 2? is the C-H bonding orbital formed by overlap of a carbon s-p hybrid orbital with the hydrogen 1s orbital. The 3? is a carbon non-bonding orbital pointing along the C-H axis away from the hydrogen, while there are two non-bonding 1? orbitals perpendicular to the C-H axis. However the 3? is an s-p hybrid which has lower energy than the 1? orbital which is pure p, so the 3? is filled before the 1?. The CH radical is in fact isoelectronic with the nitrogen atom which does have three unpaired electrons in accordance with Hund's rule of maximum multiplicity. However the nitrogen atom has three degenerate p orbitals, in contrast to the CH radical where hybridization of one orbital (the 3?) leads to an energy difference.
A carbyne can occur as a short-lived reactive intermediate. For instance, fluoromethylidyne (CF) can be detected in the gas phase by spectroscopy as an intermediate in the flash photolysis of CHFBr2.
Carbynes can act as trivalent ligands in complexes with transition metals, in which they are connected to a metal by the three non-bonded electrons in the -C3o group. Examples of such coordination compounds are , WBr(CO)2(2,2'-bipyridine)?C-aryl and WBr(CO)2(PPh3)2?C-NR2. Such a compound can be obtained by the reaction of tungsten hexacarbonyl W(CO)6 with lithium diisopropylamide to form (iPr2N)(OLi)C=W(CO)5. This salt is then oxidized with either oxalyl bromide or triphenylphosphine dibromide, followed by addition of triphenylphosphine. Another method is to treat a methoxy metal carbene with a Lewis acid.