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Phosphinidene
Phosphinidenes (IUPAC: phosphanylidenes, formerly phosphinediyls) are low-valent phosphorus compounds analogous to carbenes and nitrenes, having the general structure RP. The parent phosphinidine has the formula PH. More common are the organic analogues where R = alkyl or aryl. In these compounds phosphorus has only 6 electrons in its valence level. Most phosphinidenes are highly reactive and short-lived, thereby complicating empirical studies on their chemical properties. A variety of strategies have been employed to stabilize phosphinidenes (e.g. π-donation, Steric effects, steric protection, transition metal complexation), Furthermore reagents and systems have been developed that can generate and transfer phosphinidenes as intermediates in the synthesis of various organophosphorus compounds. Electronic structure Like carbenes, phosphinidenes can exist in either a singlet state or triplet state, with the triplet state typically being more stable. The stability of these st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
X-ray Crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring the angles and intensities of the X-ray diffraction, a crystallography, crystallographer can produce a three-dimensional picture of the density of electrons within the crystal and the positions of the atoms, as well as their chemical bonds, crystallographic disorder, and other information. X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences between various materials, especially minerals and alloys. The method has also revealed the structure and function of many biological molecules, including vitamins, drugs, proteins and nucleic acids such as DNA. X-ray crystall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Transition Metal Carbene Complexes
A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. Carbene complexes have been synthesized from most transition metals and f-block metals, using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. Described often as , carbene ligands are intermediate between alkyls and carbynes . Many different carbene-based reagents such as Tebbe's reagent are used in synthesis. They also feature in catalytic reactions, especially alkene metathesis, and are of value in both industrial heterogeneous and in homogeneous catalysis for laboratory- and industrial-scale preparation of fine chemicals. Classification Metal carbene complexes are often classified into two types. The Fischer carbenes, named after Ernst Otto Fischer, feature strong ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Wittig Reaction
The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most often, the Wittig reaction is used to introduce a methylene group using methylenetriphenylphosphorane (Ph3P=CH2). Using this reagent, even a sterically hindered ketone such as camphor can be converted to its methylene derivative. Reaction mechanism Mechanistic studies have focused on unstabilized ylides, because the intermediates can be followed by NMR spectroscopy. The existence and interconversion of the betaine (3a and 3b) is subject of ongoing research. For lithium-free Wittig reactions, studies support a concerted formation of the oxaphosphetane without intervention of a betaine. In particular, phosphonium ylides 1 react with carbonyl compounds 2 via a +2cycloaddition that is sometimes described as having π2s+π2a">sub>π2s+π2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Ylide
An ylide () or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons. The result can be viewed as a structure in which two adjacent atoms are connected by both a covalent and an ionic bond; normally written X+–Y−. Ylides are thus 1,2- dipolar compounds, and a subclass of zwitterions. They appear in organic chemistry as reagents or reactive intermediates. The class name "ylide" for the compound should not be confused with the suffix "-ylide". Resonance structures Many ylides may be depicted by a multiply bonded form in a resonance structure, known as the ylene form, while the actual structure lies in between both forms: : The actual bonding picture of these types of ylides is strictly zwitterionic (the structure on the right) with the strong Coulombic attractio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Zwitterion
In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively and negatively charged functional groups. : (1,2- dipolar compounds, such as ylides, are sometimes excluded from the definition.) Some zwitterions, such as amino acid zwitterions, are in chemical equilibrium with an uncharged "parent" molecule. Betaines are zwitterions that cannot isomerize to an all-neutral form, such as when the positive charge is located on a quaternary ammonium group. Similarly, a molecule containing a phosphonium group and a carboxylate group cannot isomerize. Amino acids Tautomerism of amino acids follows this stoichiometry: : The ratio of the concentrations of the two species in solution is independent of pH. It has been suggested, on the basis of theoretical analysis, that the zwitterion is stabilized in aqueous solution by hydrogen bonding with solvent water molecules. Analysis of neutron diffraction data for g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Reactivity Of Phosphinidene
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Reactivity may refer to: * Reactivity (chemistry), the rate at which a chemical substance tends to undergo a chemical reaction * Reactive programming, a property of an execution model whereby changes are automatically propagated through a dataflow network * Reactivity (psychology) * Reactivity (electronics) * Reactivity in nuclear reactions measures the nuclear chain reaction rate in nuclear reactors and nuclear weapons See also * Reactive (other) * Reactance (other) Reactance may refer to: * Electrical reactance, the opposition to a change in voltage due to capacitance (capacitive reactance) or in current due to inductance (inductive reactance); the imaginary component of AC impedance * Magnetic reactance, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Bertrand Phosphinidene HOMO-LUMO
Bertrand may refer to: Places * Bertrand, Missouri, US * Bertrand, Nebraska, US * Bertrand, New Brunswick, Canada * Bertrand Township, Michigan, US * Bertrand, Michigan * Bertrand, Virginia, US * Bertrand Creek, state of Washington * Saint-Bertrand-de-Comminges, France * Bertrand (1981–94 electoral district), in Quebec * Bertrand (electoral district), a provincial electoral district in Quebec Other * Bertrand (name) * ''Bertrand'' (steamboat), an 1865 steamboat that sank in the Missouri River * Bertrand Baudelaire, a fictional character in ''A Series of Unfortunate Events'' * Bertrand competition, an economic model where firms compete on price * Bertrand's theorem, a theorem in classical mechanics * Bertrand's postulate, a theorem about the distribution of prime numbers * Bertrand, Count of Toulouse (died 1112) * ''Bertrand'' (film), a 1964 Australian television film See also * Bertrand Gille (other) * Bertram (other) Bertram may refer to: Places *Ber ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Kenneth B
Kenneth is a given name of Gaelic origin. The name is an Anglicised form of two entirely different Gaelic personal names: ''Cainnech'' and '' Cináed''. The modern Gaelic form of ''Cainnech'' is ''Coinneach''; the name was derived from a byname meaning "handsome", "comely". Etymology The second part of the name ''Cinaed'' is derived either from the Celtic ''*aidhu'', meaning "fire", or else Brittonic ''jʉ:ð'' meaning "lord". People Fictional characters * Kenneth Widmerpool, character in Anthony Powell's novel sequence ''A Dance to the Music of Time'' * Kenneth Parcell from 30 Rock ''30 Rock'' is an American satire, satirical sitcom television series created by Tina Fey that originally aired on NBC from October 11, 2006, to January 31, 2013. The series, based on Fey's experiences as head writer for ''Saturday Night Live' ... Places In the United States: * Kenneth, Minnesota * Kenneth City, Florida In Scotland: * Inch Kenneth, an island off the west coast of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
