In chemistry a carbene is a short-lived and highly reactive organic molecule with a divalent carbon atom with only six valence electrons and the general formula: R₁R₂C:. The carbon atom is sp² hybridised with an empty p-orbital extending above and below a plane containing R₁ and R₂ and the free electron pair. // Introduction Chemistry is a large field encompassing many subdisciplines that often overlap with significant portions of other sciences. ... 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. ... four sp3-Orbitals three sp2-Orbitals 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 a divalent 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 a pair of electrons and sp2 hybrid structure. Triplet carbenes have two unpaired electrons. They may be either sp2 hybrid or linear sp hybrid. Most carbenes have nonlinear triplet ground state with the exception of carbenes with nitrogen, oxygen, sulfur atoms, and dihalocarbenes. 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...

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 Multiplicity), and are thus the most stable state. Triplet carbenes are generally stable in gaseous state while singlet carbenes are often found in aqueous media. Since singlet carbenes are excited state species, they will over time decompose into triplet carbenes if no reaction proceeds. Image File history File links Carbenes. ... The terms spin and SPIN have several meanings, including those primarily discussed as spinning: For spin in sub-atomic physics, see spin (physics) For the stalled aircraft maneuver or any of several forms of loss of control in aircraft, see spin (flight) For the periodical, see Spin Magazine For the... It has been suggested that this article or section be merged with List of Hunds rules. ... 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). ...

Singlet and triplet carbenes do not always demostrate same reactivity. Singlet carbenes generally participate in cheletropic reactions as either electrophiles or nucleophiles. Triplet carbenes should be considered to be diradicals, and participate in stepwise radical additions. Addition of singlet carbenes to olefinic double bonds is more stereoselective than that of triplet carbenes. Reactions of singlet methylene are stereospecific while those of triplet methylene are not. An electrocyclic reaction is a type of pericyclic rearrangement reaction where the net result is one pi bond being converted into one sigma bond. ... 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. ... A synonym for the more widely accepted term, alkene. ...

Image File history File links Carbene_strsp. ...

Illustrates the stereospecific reaction of a singlet methylene with an alkene

Image File history File links Carbene_nonstrsp. ...

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 are highly reactive electrophilic species. Reactivity of a particular carbene depends on the substituent groups, preparation method, reaction conditions such as presence or absence of metals. Some of the reactions carbenes can do are insertions into C-H bonds, skeletal rearragements, and additions to double and triple bonds. Alkyl carbenes intsert much more selectively than methylene, which does not differentiate between primary, secondary, and tertiary C-H bonds. 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 substance. ... 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. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... An Alkyl is a univalent radical containing only carbon and hydrogen atoms arranged in a chain. ...

Intramolecular insertion reactions present new synthetic solutions. Generally, rigid structures favor such interstions to happen. When intramolecular insertion is possible, no intermolecular insertions are seen. Rhodium and copper complexes promote carbene formation. Both inter- and intramolecular insertions are amendable to asymmetric induction by choosing chiral ligands on metal centers. Intramolecular describes a process or characteristic limited within the structure of a single, or each molecule; a property or phenomenon limited to the extent of a single, or each molecule. ... Intermolecular describes a process or characteristic that extends from one molecule to an adjacent one; a property or phenomenon that extends from one molecule to another. ... Rh redirects here. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ...

Carbenes can be stabilized as organometallic species. These transition metal carbene complexes fall into two categories: Image File history File links Carbene_intra. ... 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.

The following people whose family name is Fischer have articles: Andrea Fischer (born 1960), German politician Bobby Fischer (born 1943), (Icelandic) American chess player Edwin Fischer (1886-1960), Swiss pianist and conductor Ernst Otto Fischer (born 1918, German chemist, Nobel prizewinner Ernst Gottfried Fischer (1754–1831) German chemist developer of... Richard R. Schrock, professor at MIT and winner of the Nobel Prize in Chemistry in 2005 Ed Schrock, American politician This is a disambiguation page — a list of articles associated with the same title. ...

Generation of Carbenes

Most commonly, photolytic, thermal, or transition metal catalyzed decomposition of diazoalkanes is used to create carbene molecules. Another method is induced elimination of halogen from gem-dihalides or HX from CHX3 moiety, employing organolithium reagents. It is not certain that in these reactions actual free carbenes are formed. It is most likely that a metal-carbene complex forms. Nevertheless, these metallocarbenes (or carbenoids) give the expected products. In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc and scandium. ... The halogens are a chemical series. ... An organolithium reagent is any organic compound with a direct bond between a carbon and a lithium atom. ...

Another approach to carbene formation is formation of diazoalkane, which then decomposes to give a carbene. The process is similar to the Bamford-Stevens reaction, which gives carbenes in aprotic solvents and carbenium ions in protic solvents. Image File history File links Carbene_made. ...

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 are known as Arduengo Carbenes and 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/brown Atomic mass 10. ...

Another mode of stabilization is present in Bertrand's Carbene, which is [Bis(diisopropylamino)phosphino[trimethylsilylcarbene]. The compound is alternatively formulated as a phosphaalkyne. 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. ...

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. 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