In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms were fully ionic. It describes the degree of oxidation of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. Beside nearly-pure ionic bonding, many covalent bonds exhibit a strong ionicity, making oxidation state a useful predictor of charge.
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the trialkyl boranes.
Carbon suboxide, or tricarbon dioxide, is an organic, oxygen-containing chemical compound with formula C3O2 and structure O=C=C=C=O. Its four cumulative double bonds make it a cumulene. It is one of the stable members of the series of linear oxocarbons O=Cn=O, which also includes carbon dioxide and pentacarbon dioxide. Although if carefully purified it can exist at room temperature in the dark without decomposing, it will polymerize under certain conditions.
Sumanene is a polycyclic aromatic hydrocarbon and of scientific interest because the molecule can be considered a fragment of buckminsterfullerene. Suman means "sunflower" in both Hindi and Sanskrit. The core of the arene is a benzene ring and the periphery consists of alternating benzene rings (3) and cyclopentadiene rings (3). Unlike fullerene, sumanene has benzyl positions which are available for organic reactions.
Annulynes or dehydroannulenes are conjugated monocyclic hydrocarbons with alternating single and double bonds in addition to at least one triple bond.
A persistent carbene is an organic molecule whose natural resonance structure has a carbon atom with incomplete octet, but does not exhibit the tremendous instability typically associated with such moieties. The best-known examples and by far largest subgroup are the N-heterocyclic carbenes (NHC), in which nitrogen atoms flank the formal carbene.
A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with carbon atom having three covalent bonds, and it bears a +1 formal charge. Carbenium ions are a major subset of carbocations, which is a general term for diamagnetic carbon-based cations. In parallel with carbenium ions is another subset of carbocations, the carbonium ions with the formula R5+. In carbenium ions charge is localized. They are isoelectronic with monoboranes such as B(CH3)3.
An arenium ion in organic chemistry is a cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. For historic reasons this complex is also called a Wheland intermediate, after American chemist George Willard Wheland (1907–1976). They are also called sigma complexes. The smallest arenium ion is the benzenium ion, which is protonated benzene.
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
A halonium ion is any onium ion containing a halogen atom carrying a positive charge. This cation has the general structure R−+X−R′ where X is any halogen and no restrictions on R, this structure can be cyclic or an open chain molecular structure. Halonium ions formed from fluorine, chlorine, bromine, and iodine are called fluoronium, chloronium, bromonium, and iodonium, respectively. The 3-membered cyclic variety commonly proposed as intermediates in electrophilic halogenation may be called haliranium ions, using the Hantzsch-Widman nomenclature system.
In organic chemistry, propellane is any member of a class of polycyclic hydrocarbons, whose carbon skeleton consists of three rings of carbon atoms sharing a common carbon–carbon covalent bond. The concept was introduced in 1966 by D. Ginsburg Propellanes with small cycles are highly strained and unstable, and are easily turned into polymers with interesting structures, such as staffanes. Partly for these reasons, they have been the object of much research.
Atomic carbon, systematically named carbon and λ0-methane, is a colourless gaseous inorganic chemical with the chemical formula C. It is kinetically unstable at ambient temperature and pressure, being removed through autopolymerisation.
The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry, and relatively short, due to its partial ionic character. The bond also strengthens and shortens as more fluorines are added to the same carbon on a chemical compound. As such, fluoroalkanes like tetrafluoromethane are some of the most unreactive organic compounds.
In organic chemistry, the di-π-methane rearrangement is the photochemical rearrangement of a molecule that contains two π-systems separated by a saturated carbon atom. In the aliphatic case, this molecules is a 1,4-diene; in the aromatic case, an allyl-substituted arene. The reaction forms (respectively) an ene- or aryl-substituted cyclopropane. Formally, it amounts to a 1,2 shift of one ene group or the aryl group, followed by bond formation between the lateral carbons of the non-migrating moiety:
Biphenylene is an organic compound with the formula (C6H4)2. It is a pale, yellowish solid with a hay-like odor. Despite its unusual structure, it behaves like a traditional polycyclic aromatic hydrocarbon.
Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula C12H18 and the condensed structural formula C6(CH3)6. It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929, Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a historically significant result, both for the field of X-ray crystallography and for understanding aromaticity.
Eluvathingal Devassy Jemmis is a professor of theoretical chemistry at the Indian Institute of Science, Bangalore, India. He was the founding director of Indian Institute of Science Education and Research, Thiruvananthapuram (IISER-TVM). His primary area of research is applied theoretical chemistry with emphasis on structure, bonding and reactivity, across the periodic table of the elements. Apart from many of his contributions to applied theoretical chemistry, an equivalent of the structural chemistry of carbon, as exemplified by the Huckel 4n+2 Rule, benzenoid aromatics and graphite, and tetrahedral carbon and diamond, is brought in the structural chemistry of boron by the Jemmis mno rules which relates polyhedral and macropolyhedral boranes to allotropes of boron and boron-rich solids. He has been awarded Padma Shri in Science and Engineering category by the Government of India.
In chemistry, the Jemmis mno rules represent a unified rule for predicting and systematizing structures of compounds, usually clusters. The rules involve electron counting. They were formulated by E. D. Jemmis to explain the structures of condensed polyhedral boranes such as B20H16, which are obtained by condensing polyhedral boranes by sharing a triangular face, an edge, a single vertex, or four vertices. These rules are additions and extensions to Wade's rules and polyhedral skeletal electron pair theory. The Jemmis mno rule provides the relationship between polyhedral boranes, condensed polyhedral boranes, and β-rhombohedral boron. This is similar to the relationship between benzene, condensed benzenoid aromatics, and graphite, shown by Hückel's 4n + 2 rule, as well as the relationship between tetracoordinate tetrahedral carbon compounds and diamond. The Jemmis mno rules reduce to Hückel's rule when restricted to two dimensions and reduce to Wade's rules when restricted to one polyhedron.
Tricarbon monoxide C3O is a reactive radical oxocarbon molecule found in space, and which can be made as a transient substance in the laboratory. It can be trapped in an inert gas matrix or made as a short lived gas. C3O can be classified as a ketene or an oxocumulene a kind of heterocumulene.
