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Phosphorane
A phosphorane (IUPAC name: λ5-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. It has the general formula PR5. The parent hydride compound is the hypothetical molecule PH5. The derivative pentaphenylphosphorane (Ph5P) is stable. Phosphoranes adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds. Hypervalent bonding is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule phosphorus pentafluoride.G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, . Phosphoranes of the type R3P=CR2 are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphorane
A phosphorane (IUPAC name: λ5-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. It has the general formula PR5. The parent hydride compound is the hypothetical molecule PH5. The derivative pentaphenylphosphorane (Ph5P) is stable. Phosphoranes adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds. Hypervalent bonding is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule phosphorus pentafluoride.G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, . Phosphoranes of the type R3P=CR2 are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organophosphorus Chemistry
Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX (nerve agent), VX nerve agents. Organophosphorus chemistry is the corresponding science of the properties and reactivity of organophosphorus compounds. Phosphorus, like nitrogen, is in pnictogen, group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties. The definition of organophosphorus compounds is variable, which can lead to confusion. In industrial and environmental chemistry, an organophosphorus compound need contain only an organic substituent, but need not have a direct phosphorus-carbon (P-C) bond. Thus a large proportion of pesticides (e.g., malathion), are often included in this class of compound ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organophosphorus Chemistry
Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX (nerve agent), VX nerve agents. Organophosphorus chemistry is the corresponding science of the properties and reactivity of organophosphorus compounds. Phosphorus, like nitrogen, is in pnictogen, group 15 of the periodic table, and thus phosphorus compounds and nitrogen compounds have many similar properties. The definition of organophosphorus compounds is variable, which can lead to confusion. In industrial and environmental chemistry, an organophosphorus compound need contain only an organic substituent, but need not have a direct phosphorus-carbon (P-C) bond. Thus a large proportion of pesticides (e.g., malathion), are often included in this class of compound ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. Stereochemistry For the reaction with aldehydes, the double bond geometry is readily predicted based on the nature of the ylide. With unstabilised ylides (R3 = alkyl) this results in (''Z'')-alkene product with moderate to high selectivity. With stabilized ylides (R3 = ester or ketone), the (''E'')-alkene is formed with high selectivity. The (''E'')/(''Z'') selectivity is often poor with semistabilized ylides (R3 = aryl). To obtain the (''E'')-alkene for unstabilized ylides, the Schlosser modification of the W ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphorus Pentafluoride
Phosphorus pentafluoride, P F5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air. Preparation Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, which remains a favored method: :3 PCl5 + 5 AsF3 → 3 PF5 + 5 AsCl3 Structure Single-crystal X-ray studies indicate that the PF5 has trigonal bipyramidal geometry. Thus it has two distinct types of P−F bonds (axial and equatorial): the length of an axial P−F bond is distinct from the equatorial P−F bond in the solid phase, but not the liquid or gas phases due to Berry pseudo rotation. Fluorine-19 NMR spectroscopy, even at temperatures as low as −100 °C, fails to distinguish the axial from the equatorial fluorine environments. The apparent equivalency arises from the low barrier for pseudorotation via the Berry mechanism, by which the axial and equatorial fluorine atoms rapidly exchange position ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphane
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (). With traces of present, is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure. Phosphines are compounds that include and the organophosphines, which are derived from by substituting one or more hydrogen atoms with organic groups. They have the general formula . Phosphanes are saturated phosphorus hydrides of the form , such as triphosphane. Phosphine, PH3, is the smallest of the phosphines and the smallest of the phosphanes. History Philippe Gengembre (1764–1838), a student of Lavoisier, fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Methylenetriphenylphosphorane
Methylenetriphenylphosphorane is an organophosphorus compound with the formula Ph3PCH2. It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species. Preparation and use Methylenetriphenylphosphorane is prepared from methyltriphenylphosphonium bromide by its deprotonation using a strong base like butyllithium: :Ph3PCH3Br + BuLi → Ph3PCH2 + LiBr + BuH The phosphorane is generally not isolated, instead it is used in situ. The estimated pKa of this carbon acid is near 15. Potassium tert-butoxide has been used in place of butyl lithium. Sodium amide has also been used a base. Methylenetriphenylphosphorane is used to replace oxygen centres in aldehydes and ketones with a methylene group, i.e., a methylenation: :R2CO + Ph3PCH2 → R2C=CH2 + Ph3PO The phosphorus-containing product is triphenylphosphine oxide. Structure Crystallographic characterization of the colourless ylide reveals that the phosphorus atom is approx ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reagent
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a substance ''consumed'' in the course of a chemical reaction. ''Solvents'', though involved in the reaction mechanism, are usually not called reactants. Similarly, ''catalysts'' are not consumed by the reaction, so they are not reactants. In biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates. Definitions Organic chemistry In organic chemistry, the term "reagent" denotes a chemical ingredient (a compound or mixture, typically of inorganic or small organic molecules) introduced to cause the desired transformation of an organic substance. Examples include the Collins reagent, Fenton's reagent, and Grignard reagents. Analytical chemistry In analytical chemistry, a reagent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 multiple bond 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 attraction between the " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apical (chemistry)
In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not identical (see also pentagonal bipyramid), because there is no geometrical arrangement with five terminal atoms in equivalent positions. Examples of this molecular geometry are phosphorus pentafluoride (), and phosphorus pentachloride () in the gas phase. Axial (or apical) and equatorial positions The five atoms bonded to the central atom are not all equivalent, and two different types of position are defined. For phosphorus pentachloride as an example, the phosphorus atom shares a plane with three chlorine atoms at 120° angles to each other in ''equatorial'' positions, and two more chlorine atoms above and below the plane (''axial'' or ''apical'' positions). According to the VSEPR theory of molecular geometry, an axial position is more crowd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypervalent Molecule
In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pentachloride (), sulfur hexafluoride (), chlorine trifluoride (), the chlorite () ion, and the triiodide () ion are examples of hypervalent molecules. Definitions and nomenclature Hypervalent molecules were first formally defined by Jeremy I. Musher in 1969 as molecules having central atoms of group 15–18 in any valence other than the lowest (i.e. 3, 2, 1, 0 for Groups 15, 16, 17, 18 respectively, based on the octet rule). Several specific classes of hypervalent molecules exist: * Hypervalent iodine compounds are useful reagents in organic chemistry (e.g. Dess–Martin periodinane) * Tetra-, penta- and hexavalent phosphorus, silicon, and sulfur compounds (e.g. PCl5, PF5, SF6, sulfuranes and persulfuranes) * Noble gas compounds (ex. xe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is a member of the International Science Council (ISC). IUPAC is registered in Zürich, Switzerland, and the administrative office, known as the "IUPAC Secretariat", is in Research Triangle Park, North Carolina, United States. This administrative office is headed by IUPAC's executive director, currently Lynn Soby. IUPAC was established in 1919 as the successor of the International Congress of Applied Chemistry for the advancement of chemistry. Its members, the National Adhering Organizations, can be national chemistry societies, national academies of sciences, or other bodies representing chemists. There are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPAC's Inter-divisional Committee on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
