In chemistry, a hypervalent molecule 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 in chlorous acid and the triiodide ion are examples of hypervalent molecules.
The 1,3-dipolar cycloaddition is a chemical reaction between a 1,3-dipole and a dipolarophile to form a five-membered ring. The earliest 1,3-dipolar cycloadditions were described in the late 19th century to the early 20th century, following the discovery of 1,3-dipoles. Mechanistic investigation and synthetic application were established in the 1960s, primarily through the work of Rolf Huisgen. Hence, the reaction is sometimes referred to as the Huisgen cycloaddition. 1,3-dipolar cycloaddition is an important route to the regio- and stereoselective synthesis of five-membered heterocycles and their ring-opened acyclic derivatives. The dipolarophile is typically an alkene or alkyne, but can be other pi systems. When the dipolarophile is an alkyne, aromatic rings are generally produced.
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides/oxychlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.
Methyllithium is the simplest organolithium reagent, with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in solution with an ether as the solvent, is a reagent in organic synthesis as well as organometallic chemistry. Operations involving methyllithium require anhydrous conditions, because the compound is highly reactive towards water. Oxygen and carbon dioxide are also incompatible with MeLi. Methyllithium is usually not prepared, but purchased as a solution in various ethers.
Hexamethyltungsten is the chemical compound W(CH3)6 also written WMe6. Classified as a transition metal alkyl complex, hexamethyltungsten is an air-sensitive, red, crystalline solid at room temperature; however, it is extremely volatile and sublimes at −30 °C. Owing to its six methyl groups it is extremely soluble in petroleum, aromatic hydrocarbons, ethers, carbon disulfide, and carbon tetrachloride.
Organobismuth chemistry is the chemistry of organometallic compounds containing a carbon to bismuth chemical bond. Applications are few. The main bismuth oxidation states are Bi(III) and Bi(V) as in all higher group 15 elements. The energy of a bond to carbon in this group decreases in the order P > As > Sb > Bi. The first reported use of bismuth in organic chemistry was in oxidation of alcohols by Frederick Challenger in 1934 (using Ph3Bi(OH)2). Knowledge about methylated species of bismuth in environmental and biological media is limited.
Organomolybdenum chemistry is the chemistry of chemical compounds with Mo-C bonds. The heavier group 6 elements molybdenum and tungsten form organometallic compounds similar to those in organochromium chemistry but higher oxidation states tend to be more common.
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.
In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AOmXn, where X is a halogen. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I) in their molecules. The element A may be a main group element, a transition element, a rare earth element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.
A pyramidal carbocation is a type of carbocation with a specific configuration. This ion exists as a third class, besides the classical and non-classical ions. In these ions, a single carbon atom hovers over a four- or five-sided polygon, in effect forming a pyramid. The four-sided pyramidal ion will carry a charge of 1+, and the five-sided pyramid will carry 2+. In the images, the black spot on the vertical line represents the hovering carbon atom.
Pentamethylarsenic (or pentamethylarsorane)is an organometalllic compound containing five methyl groups bound to an arsenic atom with formula As(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid.
Pentamethylantimony or pentamethylstiborane is an organometalllic compound containing five methyl groups bound to an antimony atom with formula Sb(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramid. Some other antimony(V) organometallic compounds include pentapropynylantimony (Sb(CCCH3)5) and pentaphenyl antimony (Sb(C6H5)5). Other known pentamethyl-pnictides include pentamethylbismuth and pentamethylarsenic.
Pentamethyltantalum is a homoleptic organotantalum compound. It has a propensity to explode when it is melted. Its discovery was part of a sequence that led to Richard R. Schrock's Nobel Prize winning discovery in olefin metathesis.
Trisilaallene is a subclass of silene derivatives where a central silicon atom forms double bonds with each of two terminal silicon atoms, with the generic formula R2Si=Si=SiR2. Trisilaallene is a silicon-based analog of an allene, but their chemical properties are markedly different.
Tellurophenes are the tellurium analogue of thiophenes and selenophenes.
(Pentamethylcyclopentadienyl)aluminium(I) is an organometallic compound with the formula Al(C5Me5) ("Me" is a methyl group; CH3). The compound is often abbreviated to AlCp* or Cp*Al, where Cp* is the pentamethylcyclopentadienide anion (C5Me5−). Discovered in 1991 by Dohmeier et al., AlCp* serves as the first ever documented example of a room temperature stable monovalent aluminium compound. In its isolated form, Cp*Al exists as the tetramer [Cp*Al]4, and is a yellow crystal that decomposes at temperatures above 100 °C but also sublimes at temperatures above 140 °C.
Nontrigonal pnictogen compounds refer to tricoordinate trivalent pnictogen compounds that are not of typical trigonal pyramidal molecular geometry. By virtue of their geometric constraint, these compounds exhibit distinct electronic structures and reactivities, which bestow on them potential to provide unique nonmetal platforms for bond cleavage reactions.
(Trimethylsilyl)methyllithium is classified both as an organolithium compound and an organosilicon compound. It has the empirical formula LiCH2Si(CH3)3, often abbreviated LiCH2TMS. It crystallizes as the hexagonal prismatic hexamer [LiCH2TMS]6, akin to some polymorphs of methyllithium. Many adducts have been characterized including the diethyl ether complexed cubane [Li4(μ3-CH2TMS)4(Et2O)2] and [Li2(μ-CH2TMS)2(TMEDA)2].
Bismuthinidenes are a class of organobismuth compounds, analogous to carbenes. These compounds have the general form R-Bi, with two lone pairs of electrons on the central bismuth(I) atom. Due to the unusually low valency and oxidation state of +1, most bismuthinidenes are reactive and unstable, though in recent decades, both transition metals and polydentate chelating Lewis base ligands have been employed to stabilize the low-valent bismuth(I) center through steric protection and π donation either in solution or in crystal structures. Lewis base-stabilized bismuthinidenes adopt a singlet ground state with an inert lone pair of electrons in the 6s orbital. A second lone pair in a 6p orbital and a single empty 6p orbital make Lewis base-stabilized bismuthinidenes ambiphilic.
Molybdenum difluoride dioxide is the inorganic compound with the formula MoF2O2. It is a white, diamagnetic, volatile solid.
