Linear acetylenic carbon
Encyclopedia
Linear acetylenic carbon (LAC), also called carbyne
, is an allotrope of carbon
that has the chemical structure -(C≡C)n- as a repeating chain.
The carbon atoms in this form are each linear in geometry with sp orbital hybridisation
: it is a polymer
with alternating single and triple bonds. This type of carbyne is of considerable interest to nanotechnology
as its Young's modulus
is forty times that of diamond
, the hardest known material. The existence of carbyne itself as a carbon allotrope is controversial, as the properties and synthetic methods seem consistent with generation of fullerene
s. However, polyalkyne oligomers called polyyne
s as substructures of larger compounds are well known and actively researched as a substitute. Carbyne chains of over 300 carbons have been prepared and appear to be reasonably stable as long as the terminal alkynes on the chain are capped rather than having a free acetylenic H atom. The analysis in this study specifically demonstrated that the result was a carbyne-like structure rather than a fullerene.
An analysis of a synthesized linear carbon allotrope found it to have a cumulene
electronic structure—sequential double bond
s along an sp-hybridized carbon chain—rather than the alternating triple–single pattern of linear carbyne.
Carbyne
In chemistry, a carbyne is a monovalent carbon radical species containing an electrically neutral univalent carbon atom with three non-bonded electrons.- Gas phase/reactive intermediate :...
, is an allotrope of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
that has the chemical structure -(C≡C)n- as a repeating chain.
The carbon atoms in this form are each linear in geometry with sp orbital hybridisation
Orbital hybridisation
In chemistry, hybridisation is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. Hybridised orbitals are very useful in the explanation of the shape of molecular orbitals for molecules. It is an integral part...
: it is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
with alternating single and triple bonds. This type of carbyne is of considerable interest to nanotechnology
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
as its Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...
is forty times that of diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
, the hardest known material. The existence of carbyne itself as a carbon allotrope is controversial, as the properties and synthetic methods seem consistent with generation of fullerene
Fullerene
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...
s. However, polyalkyne oligomers called 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 as substructures of larger compounds are well known and actively researched as a substitute. Carbyne chains of over 300 carbons have been prepared and appear to be reasonably stable as long as the terminal alkynes on the chain are capped rather than having a free acetylenic H atom. The analysis in this study specifically demonstrated that the result was a carbyne-like structure rather than a fullerene.
An analysis of a synthesized linear carbon allotrope found it to have a cumulene
Cumulene
A cumulene is a chemical compound with two or more cumulative double bonds, for example butatriene , H2C=C=C=CH2. Unlike alkanes and most alkenes, cumulenes tend to be rigid, which makes them appealing for molecular nanotechnology. Polyynes are another kind of rigid carbon chains...
electronic structure—sequential double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
s along an sp-hybridized carbon chain—rather than the alternating triple–single pattern of linear carbyne.