Cumulene
Encyclopedia
A cumulene is a chemical compound
with two or more cumulative (consecutive) double bonds
, for example butatriene (which is also just called cumulene), H2C=C=C=CH2. Unlike alkane
s and most alkene
s, cumulenes tend to be rigid, which makes them appealing for molecular nanotechnology
. Polyyne
s are another kind of rigid carbon chains. Cumulenes are found in regions of space where hydrogen is rare. See astrochemistry
.
Inorganic cumulenes include carbon suboxide
. An important class of organic cumulenes are ketene
s, which are intermediate in character between CO2 and allene.
and Fe(CO)5
Structurally, this molecule resembles Fe2(CO)9
, wherein one μ-CO ligand is replaced by 1,1-diphenylvinylidene, Ph2C2. The first monometallic vinylidene complex was (C5H5
)Mo(P(C6H5)3
)(CO)2[C=C(CN)2]Cl.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with two or more cumulative (consecutive) double bonds
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
, for example butatriene (which is also just called cumulene), H2C=C=C=CH2. Unlike alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
s and most alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s, cumulenes tend to be rigid, which makes them appealing for molecular nanotechnology
Molecular nanotechnology
Molecular nanotechnology is a technology based on the ability to build structures to complex, atomic specifications by means of mechanosynthesis. This is distinct from nanoscale materials...
. Polyyne
Polyyne
The polyynes are a group of organic compounds with alternating single and triple bonds. The simplest example is diacetylene or buta-1,3-diyne, HC≡C-C≡CH....
s are another kind of rigid carbon chains. Cumulenes are found in regions of space where hydrogen is rare. See astrochemistry
Astrochemistry
Astrochemistry is the study of the abundance and reactions of chemical elements and molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium...
.
Carbon suboxide
Carbon suboxide, or tricarbon dioxide, is an oxide of carbon with chemical formula C3O2 or O=C=C=C=O. Its four cumulative double bonds make it a cumulene...
. An important class of organic cumulenes are ketene
Ketene
A ketene is an organic compound of the form R'RC=C=O. The term is also used specifically to mean ethenone, the simplest ketene, where R' and R are hydrogen atoms.Ketenes were first studied as a class by Hermann Staudinger.-Formation:...
s, which are intermediate in character between CO2 and allene.
Structure
The rigidity of cumulenes arises from the fact that the internal carbon atoms carry two double bonds. Their sp hybridisation results in two bonds separated by 90°. Interestingly, cumulenes with (1) an even number of consecutive double bonds and (2) dissimilar substituents on either end can be chiral even though they lack a classical stereocenter. For example, penta-2,3-diene and hexa-1,3,4-triene are chiral. On the other hand odd numbers of double bonds in a cumulated system with proper substituents show cis-trans isomerism.Reactions
The reactions of cumulene are those of the isolated double bond. Although this molecule possesses two π-bonds in very close vicinity, in essence these act as isolated double bonds. This is because the two π-bonds on the central carbon atom are formed by the non-hybridised p-orbitals. As these orbitals are perpendicular towards each other and occupy each other's nodal planes the two bonds are in essence isolated.Transition metal cumulenes
The first reported complex containing a vinylidene ligand was (Ph2C2Fe2(CO)8, derived from the reaction of diphenylketeneDiphenylketene
Diphenylketene is a chemical of the ketene family. Diphenylketene, like most disubstituted ketenes is a red/orange oil at room temperature and pressure.-Chemistry and reactivity:...
and Fe(CO)5
Iron pentacarbonyl
Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula 5. Under standard conditions Fe5 is a free-flowing, straw-colored liquid with a pungent odour. This compound is a common precursor to diverse iron compounds, including many that are useful in organic synthesis. Fe5 is...
Structurally, this molecule resembles Fe2(CO)9
Diiron nonacarbonyl
Diiron nonacarbonyl is an inorganic compound with the formula Fe29. This metal carbonyl is an important reagent in organometallic chemistry and of occasional use in organic synthesis. It is a more reactive source of Fe than Fe5 and less dangerous to handle because it is nonvolatile...
, wherein one μ-CO ligand is replaced by 1,1-diphenylvinylidene, Ph2C2. The first monometallic vinylidene complex was (C5H5
Cyclopentadienyl
In organic chemistry, cyclopentadienyl is a cyclic group of atoms with the formula C5H5. Cyclopentadienyl are closely related to cyclopentadiene. Cyclopentadienyl have five carbon atoms bonded together in a pentagonal planar ring, all five of which are bonded to individual hydrogen atoms...
)Mo(P(C6H5)3
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
)(CO)2[C=C(CN)2]Cl.
External links
- IUPAC Gold BookGold BookThe Compendium of Chemical Terminology is a book published by the International Union of Pure and Applied Chemistry containing internationally accepted definitions for terms in chemistry...
IUPACs definition of cumulenes