In chemistry a carbene is a short-lived and highly reactive organic molecule with a divalent carbon atom with only 6 valence electrons and the general formula: R₁R₂C:. The carbon atom is sp² hybridised with a empty p-orbital extending above and below a plane containing R₁ and R₂ and the free electron pair. Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... Organic has several meanings and related topics. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Valence is a scientific term in chemistry to describe electrons in the outermost orbital. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Valence is a scientific term in chemistry to describe electrons in the outermost orbital. ... In chemistry, hybridisation is the mixing of atomic orbitals belonging to a same electron shell to form new orbitals suitable for the qualitative description of atomic bonding properties. ... A lone pair is an electron pair without bonding or sharing with other atoms. ...

The parent carbene is H₂C: also called methylene. An often encountered carbene is Cl₂C: or dichlorocarbene which can be generated in situ from chloroform and a strong base. In chemistry, methylene is di-valent functional group CH2 derived formally from methane. ... In situ (in place in Latin), a term used in: biology, where it means to examine the phenomenon exactly in place where it occurs (without removing it in some special medium etc. ... PEL-TWA (OSHA) 50 ppm (240 mg/m3) IDLH (NIOSH) 500 ppm Flash point non-flammable RTECS number FS9100000 Supplementary data page Structure & properties n, εr, etc. ... A base is: in mathematics: A number that is raised to a power, or base of an exponential function. ...

Generally there are two types of carbenes; singlet or triplet carbenes. Singlet carbenes have their electrons paired; triplet carbenes have their electrons unpaired (the nomenclature difference comes from disparate signatures in EPR spectra). Singlet and triplet carbenes are named so because of the electronic spins they posses: The total spin of singlet carbenes is one while that of triplet carbenes is three (calcuated as total number of unpaired electrons+1). Triplet carbenes usually have energies 30-40 KJ/mol lower than singlet carbenes (See also Hund's rule of Maximum Multiplicy), and are thus the most stable state. Triplet carbenes are genrally stable in gaeuos state while singlet carbenes are often found in aqueous media. Singlet carbenes generally participate in cheleotropic reactions as either electrophiles or nucleophiles. Triplet carbenes should be considered to be diradicals, and participate in stepwise radical additions. Since singlet carbenes are excited state species, they will over time decompose into triplet carbenes if no reaction proceeds. In theoretical physics, a singlet usually refers to a one-dimensional representation (e. ... A triplet is a set of three items, and includes in particular: one of three babies in a multiple birth a preparation of opal as a gemstone, with a thin layer of opal backed with a dark material and covered with cap of clear quartz in poetry, a tercet (three... Properties The electron is a subatomic particle. ... Nomenclature is a system of naming and categorizing objects in a given category. ... EPR may refer to the following: Electron paramagnetic resonance, more commonly called Electron spin resonance, used especially in Analytical Chemistry EPR paradox by Einstein, Podolsky and Rosen (Quantum Mechanics) Extended producer responsibility European Pressurized Reactor Enlisted Performance Report, an evaluation form used by the United States Air Force Ejército Popular... In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ... In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). ...

Moreover, reactions of singlet methylene is stereospecific while that of triplet methylene are not.

Illustrates the stereospecific reaction of a singlet methylene with an alkene

Illustrates the non-stereospecific reaction of a triplet methylene with an alkene

The reaction of methylene generated from photolysis of diazomethane with cis-2-butene and trans-2-butene is stereospecific which proves that in this reaction methylene is a singlet.¹ Photolysis refers to any chemical reaction in which a compound is broken down by light. ... A diazo compund is any class of organic substances that have the characteristic atomic grouping: as a part of their molecular structure. ... In chemistry, a stereospecific chemical reaction yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditions. ...

skell analysis of carbene File links The following pages link to this file: Carbenes ...

Carbenes can be stabilized as organometallic species. These transition metal carbene complexes fall into two categories: Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. ... A transition metal carbene complex is a compound bearing a formal carbon-metal double bond. ...

• Fischer carbenes in which carbenes are tethered to a metal and an electron-withdrawing group (usually a carbonyl),
• schrock carbenes; in which carbenes are tethered to a metal and an electron-donating group. The reactions that such carbenes participate in are very different from those in which organic carbenes participate.

Persistent carbenes

A carbene is a reactive intermediate but certain organic carbenes, so called persistent carbenes, discovered in the 1990's are also quite stable. Singlet carbenes derived from imidazolium or thiazolium salts, for example, can be crystallized and isolated as free carbenes and stored without chemical decomposition, if kept in an oxygen- and moisture-free atmosphere ² In chemistry a reactive intermediate is a short-lived high energy highly reactive molecule. ... Imidazole is a heterocyclic aromatic organic compound. ... chemical decomposition is the gradual fragmentation of a chemical compound into smaller molecules. ...

One stable N-heterocyclic Carbene ³ has a structure analogous to borazine with one boron atom replaced by methylene. This results in a planar 6 electron compound. stable imidazolium carbene File links The following pages link to this file: Carbenes ... Adamantane (Tricyclo[3. ... In organic chemistry, a substituent is an atom or group of atoms subsituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... Borazine is an inorganic compound composed of the elements boron, nitrogen and hydrogen. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black Atomic mass 10. ...

In 2001, Hideo Tomioka and his associates were able to produce a comparatively stable triplet carbene, taking advantage of resonance. Triplet bis(9-anthryl)carbene ⁴ has a half-life of 19 minutes. Image File history File links Borazine carbene File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Lithium tetramethylpiperidide or LiTMP (CAS 38227-87-1) is an organic base and a harpoon base. ... A cyclohexane molecule in chair conformation, with hydrogen atoms in axial position in red, equatorial in blue. ... Resonance structures are diagrammatic tools in organic chemistry to symbolize resonant bonds between atoms in molecules. ...

References

• ^[1] Structure of Carbene CH2 Philip S. Skell, Robert C. Woodworth; J. Am. Chem. Soc.; 1956; 78(17); 4496-4497. Abstract
• ^[2] A stable crystalline carbene Anthony J. Arduengo, , III Richard L. Harlow, Michael Kline; J. Am. Chem. Soc.; 1991; 113(1); 361-363. Abstract
• ^[3] Stable Planar Six--Electron Six-Membered N-Heterocyclic Carbenes with Tunable Electronic Properties Carsten Präsang, Bruno Donnadieu, and Guy Bertrand J. Am. Chem. Soc.; 2005; 127(29) pp 10182 - 10183 Abstract
• ^[4] Nature, 412, 626 (2001), also see [1]
• ^[5] Organic Chemistry R.T Morrison, R.N Boyd pp 473-478