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Di-π-methane Rearrangement
The di-π-methane rearrangement is a photochemical reaction of a molecular entity that contains two π-systems separated by a saturated carbon atom (a 1,4-diene or an allyl-substituted aromatic ring), to form an ene- (or aryl-) substituted cyclopropane. The rearrangement reaction formally amounts to a 1,2 shift of one ene group (in the diene) or the aryl group (in the allyl-aromatic analog) and bond ''formation'' between the lateral carbons of the non-migrating moiety. Discovery and mechanism This rearrangement was originally encountered in the photolysis of barrelene to give semibullvalene. Once the mechanism was recognized as general by Howard Zimmerman in 1967, it was clear that the structural requirement was having two pi groups attached to an sp3-hybridized carbon, and then a variety of further examples was obtained. One was the photolysis of the ''Mariano Compound'', 3,3-dimethyl-1,1,5,5-tetraphenyl-1,4-pentadiene. Another was the reaction of the ''Pratt diene'' Equat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mechanistic Organic Photochemistry
Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ultraviolet lamps are employed. Organic photochemistry has proven to be a very useful synthetic tool. Complex organic products can be obtained simply. History Early examples were often uncovered by the observation of precipitates or color changes from samples that were exposed to sunlights. The first reported case was by Ciamician that sunlight converted santonin to a yellow photoproduct: An early example of a precipitate was the photodimerization of anthracene, characterized by Yulii Fedorovich Fritzsche and confirmed by Elbs. Similar observations focused on the dimerization of cinnamic acid to truxillic acid. Many photodimers are now recognized, e.g. pyrimidine dimer, thiophosgene, diamantane. Another example was uncovered by Egb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semibullvalene
Bullvalene is a hydrocarbon with the chemical formula . The molecule has a cage-like structure formed by the fusion of one cyclopropane and three cyclohepta-1,4-diene rings. Bullvalene is unusual as an organic molecule due to the and bonds forming and breaking rapidly on the NMR timescale; this property makes it a fluxional molecule. Stereodynamics The bullvalene molecule is a cyclopropane platform with three vinylene arms conjoined at a methine group. This arrangement enables a degenerate Cope rearrangement with the result that all carbon atoms and hydrogen atoms appear equivalent on the NMR timescale. At room temperature the 1H NMR signals average to a rounded peak at 5.76 ppm. At lower temperatures the peak broadens into a mound-like appearance, and at very low temperatures the fluxional behavior of bullvalene is reduced, allowing for 4 total signals to be seen. This pattern is consistent with an exchange process whose rate ''k'' is close to the frequency separation of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barr To Semibullvalene Mech
Barr may refer to: Places * Barr (placename element), element of place names meaning 'wooded hill', 'natural barrier' * Barr, Ayrshire, a village in Scotland * Barr Building (Washington, DC), listed on the US National Register of Historic Places * Barr Castle, ruin in Renfrewshire, Scotland * Barr Castle, in Galston, East Ayrshire, Scotland * Barr, Bas-Rhin, a commune of the Bas-Rhin ''département'' in France * Barr Township, Daviess County, Indiana, US * Barr Township, Cambria County, Pennsylvania, US Companies * A.G. Barr, a Scottish soft drinks manufacturer * Barr Construction Ltd, a Scottish construction company * Barr Pharmaceuticals, a generic drug manufacturer that was acquired by Teva Pharmaceutical in 2008 People * Barr (surname) * Brendan Fowler, a.k.a. BARR, American musician * Barr (tribe), a people in southwest Asia Other uses * Barr body, the inactive chromosome in a somatic cell * Al-Barr, one of the names of God in Islam See also * Barre (disambigua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigma Bond
In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is symmetrical with respect to rotation about the bond axis. By this definition, common forms of sigma bonds are s+s, pz+pz, s+pz and dz2+dz2 (where z is defined as the axis of the bond or the internuclear axis). Quantum theory also indicates that molecular orbitals (MO) of identical symmetry actually mix or ''hybridize''. As a practical consequence of this mixing of diatomic molecules, the wavefunctions s+s and pz+pz molecular orbitals become blended. The extent of this mixing (or hybridization or blending) depends on the relative energies of the MOs of like symmetry. For homodiatomics (homonuclear diatomic molecules), bonding σ orbitals have no nodal planes at which the wavefunction i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intersystem Crossing
Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity. Excited Singlet and Triplet States When an electron in a molecule with a singlet ground state is excited (''via'' absorption of radiation) to a higher energy level, either an excited singlet state or an excited triplet state will form. Singlet state is a molecular electronic state such that all electron spins are paired. That is, the spin of the excited electron is still paired with the ground state electron (a pair of electrons in the same energy level must have opposite spins, per the Pauli exclusion principle). In a triplet state the excited electron is no longer paired with the ground state electron; that is, they are parallel (same spin). Since excitation to a triplet state involves an additional "forbidden" spin transition, it is less probable that a triplet state will form when the molecule absorbs radiation. W ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible with water and serves as an important organic solvent in its own right, in industry, home, and laboratory. About 6.7 million tonnes were produced worldwide in 2010, mainly for use as a solvent and production of methyl methacrylate (and from that PMMA) as well as bisphenol A.Acetone World Petrochemicals report, January 2010Stylianos Sifniades, Alan B. Levy, "Acetone" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. It is a common building block in |
Singlet State
In quantum mechanics, a singlet state usually refers to a system in which all electrons are paired. The term 'singlet' originally meant a linked set of particles whose net angular momentum is zero, that is, whose overall spin quantum number s=0. As a result, there is only one spectral line of a singlet state. In contrast, a doublet state contains one unpaired electron and shows splitting of spectral lines into a doublet; and a triplet state has two unpaired electrons and shows threefold splitting of spectral lines. History Singlets and the related spin concepts of doublets and triplets occur frequently in atomic physics and nuclear physics, where one often needs to determine the total spin of a collection of particles. Since the only observed fundamental particle with zero spin is the extremely inaccessible Higgs boson, singlets in everyday physics are necessarily composed of sets of particles whose individual spins are non-zero, e.g. or 1. The origin of the term "singlet" is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triplet State
In quantum mechanics, a triplet is a quantum state of a system with a spin of quantum number =1, such that there are three allowed values of the spin component, = −1, 0, and +1. Spin, in the context of quantum mechanics, is not a mechanical rotation but a more abstract concept that characterizes a particle's intrinsic angular momentum. It is particularly important for systems at atomic length scales, such as individual atoms, protons, or electrons. Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception. At room temperature, O2 exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive despite being thermodynamically one of the strongest oxidants. Photochemical or thermal activation can bring it into the singlet state, which makes it kinetically as well as thermodynamically a very strong oxidant. __TOC__ Two spin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pratt Wiki
Pratt is an English surname. Notable people with the surname include: A–F * Abner Pratt (1801–1863), American diplomat, jurist, politician, lawyer * Al Pratt (baseball) (1847–1937), American baseball player * Andy Pratt (baseball) (born 1979), American baseball player * Andy Pratt (singer-songwriter) (born 1947), American singer-songwriter and musician * Antwerp Edgar Pratt (1852-1924), British naturalist, explorer, collector of plants and animals * Awadagin Pratt (born 1966), American concert pianist * Babe Pratt (Walter Peter Pratt, 1916–1988), Canadian ice hockey player * Betty Rosenquest Pratt, (1925–2016), American tennis player * Bob Pratt (1912–2001), Australian rules footballer * Caleb S. Pratt (1832–1861), Union Officer * Charles Pratt, 1st Earl Camden (1713–1794), British lawyer * Charles Pratt (1830–1891), American businessman and philanthropist * Chris Pratt (born 1979), American actor * Christopher Pratt (born 1935), Canadian artist * Daniel Pratt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mariano
Mariano is a masculine name from the Romance languages, corresponding to the feminine Mariana. It is an Italian, Spanish and Portuguese variant of the Roman Marianus which derived from Marius, and Marius derived from the Roman god Mars (see also Ares) or from the Latin ''maris'' "male". Mariano and Marian are sometimes seen as a conjunction of the two female names Mary and Ann. This name is an homage to The Virgin Mary, Mother of Jesus. Mariano, as a surname, is of Italian, Spanish and Portuguese origin from the personal name ''Mariano'', from the Latin family name ''Marianus'' (a derivative of the ancient personal name ''Marius'', of Etruscan origin). In the early Christian era it came to be taken as an adjective derived from ''Maria'', and was associated with the cult of the Virgin Mary. It was borne by various early saints, including a 3rd-century martyr in Numibia and a 5th-century hermit of Berry, France. It is also a Sephardic Jewish surname derived from the term Merano. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Howard Zimmerman
Howard E. Zimmerman (July 5, 1926 – February 12, 2012) was a professor of chemistry at the University of Wisconsin–Madison. He was elected to the National Academy of Sciences in 1980 and the recipient of the 1986 American Institute of Chemists Chemical Pioneer Award. Biography Howard E. Zimmerman was a native of Connecticut. During World War II he served in the U.S. Armored Corps in Europe where he was a tank gunner. His final rank was technical sergeant. He obtained a B. S. in Chemistry in 1950 and a Ph.D. in 1953 both from Yale University. He was a Postdoctoral Research Fellow with a National Research Council fellowship from 1953 to 1954 working with R. B. Woodward (Harvard). From 1954 to 1960 he was assistant professor at Northwestern University. Beginning in 1960 he was Associate Professor and then Professor at the University of Wisconsin, and from 1990 he was Hilldale and A. C. Cope Professor of Chemistry. His publications number over 285 (including 11 chapters). Zimme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barrelene
Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo .2.2cta-2,5,7-triene. First synthesized and described by Howard Zimmerman in 1960, the name derives from the resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels–Alder adduct of benzene and acetylene. Due to its unusual molecular geometry, the compound is of considerable interest to theoretical chemists. Iptycenes, with the alkene groups part of an arenes, are related compounds. It is also a starting material for many other organic compounds, such as semibullvalene. The original Zimmerman, synthesis modified in 1969, starts from coumalic acid: : Many alternative routes have been devised since then, one of them starting from benzene oxide: : An alternate route that allows synthesis of the parent barrelene system and a variety of substituted barrelenes has also been reported Barrelene reactions Barrelene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
