organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...

, a carbyne is a general term for any

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

whose

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

consists of an

electrically neutral Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respectiv ...

carbon atom connected by a single covalent bond and has three non-bonded electrons. The carbon atom has either one or three unpaired

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kno ...

s, depending on its excitation state; making it a

radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

. The chemical formula can be written or (also written as ), or just CH. Carbynes can be seen as derivatives of the simplest such compound, the

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 ...

or unsubstituted carbyne or , in which the functional group is a

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxi ...

atom. Reported for the first time back in 1967 by Kasatochkin, carbyne is an infinite sp1 hybridized long linear chain of carbon, where each link is just a single carbon atom.

Electronic configuration

Carbyne molecules are generally found to be in electronic

doublet state In quantum mechanics, a doublet is a composite quantum state of a system with an effective spin of 1/2, such that there are two allowed values of the spin component, −1/2 and +1/2. Quantum systems with two possible states are sometimes called t ...

s: the non-bonding electrons on carbon are arranged as one

(unpaired electron) and one electron pair, leaving a vacant

atomic orbital In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any sp ...

, rather than being a triradical (the quartet state). The simplest case is the CH radical, which has an

electron configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom ...

. Here the 1σ

molecular orbital In chemistry, a molecular orbital is a mathematical function describing the location and wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of findin ...

is essentially the carbon 1s atomic orbital, and the 2σ is the C–H bonding orbital formed by

overlap Overlap may refer to: * In set theory, an overlap of elements shared between sets is called an intersection, as in a Venn diagram. * In music theory, overlap is a synonym for reinterpretation of a chord at the boundary of two musical phrases * Ove ...

of a carbon sp hybrid orbital with the hydrogen 1s orbital. The 3σ is a carbon

non-bonding orbital A non-bonding orbital, also known as ''non-bonding molecular orbital'' (NBMO), is a molecular orbital whose occupation by electrons neither increases nor decreases the bond order between the involved atoms. Non-bonding orbitals are often designat ...

pointing along the C–H axis away from the hydrogen, while there are two non-bonding 1π orbitals perpendicular to the C–H axis. However the 3σ is an sp hybrid which has lower energy than the 1π orbital which is pure p, so the 3σ is filled before the 1π. The CH radical is in fact

isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in the ...

with the nitrogen atom which does have three unpaired electrons in accordance with

Hund's rule of maximum multiplicity Hund's rule of maximum multiplicity is a rule based on observation of atomic spectra, which is used to predict the ground state of an atom or molecule with one or more open electronic shells. The rule states that for a given electron configuration ...

. However the nitrogen atom has three degenerate p orbitals, in contrast to the CH radical where hybridization of one orbital (the 3σ) leads to an energy difference.

Occurrence

A carbyne can occur as a short-lived

reactive intermediate In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these com ...

. For instance,

fluoromethylidyne Fluoromethylidyne is not a stable chemical species but a metastable radical containing one highly reactive carbon atom bound to one fluorine atom with the formula CF. The carbon atom has a lone-pair and a single unpaired (radical) electron in the g ...

(CF) can be detected in the gas phase by spectroscopy as an intermediate in the

flash photolysis Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a flash ...

of CHFBr₂. Carbynes can act as trivalent

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...

s in complexes with transition metals, in which they are connected to a

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typica ...

by the three non-bonded electrons in the –C^3• group. Examples of such

coordination compound A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

s are , W Br( CO)₂(

2,2'-bipyridine The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline o ...

)≡ C-

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used as ...

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 Lithium diisopropylamide (commonly abbreviated LDA) is a chemical compound with the molecular formula . It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature ...

to form ( ⁱPr₂N)(OLi)C=W(CO)₅. This salt is then oxidized with either

oxalyl bromide The oxalyl cation, also known as ''oxalic'', has the chemical formula 2O2sup>2+. It is the cation derived from oxalic acid. Chemical compounds containing the oxalyl cation include: Related compounds/ions *Oxalic acid, C2O4H2 *The oxalate anion, ...

or triphenylphosphine dibromide, followed by addition of

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists a ...

. Another method is to treat a methoxy metal

carbene In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" ma ...

with a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

References

{{Reflist Free radicals Organometallic chemistry