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Sigmatropic
A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one σ-bond is changed to another σ-bond in an uncatalyzed intramolecular reaction. The name ''sigmatropic'' is the result of a compounding of the long-established sigma designation from single carbon–carbon bonds and the Greek word ''tropos'', meaning turn. In this type of rearrangement reaction, a substituent moves from one part of a π-bonded system to another part in an intramolecular reaction with simultaneous rearrangement of the π system. True sigmatropic reactions are usually uncatalyzed, although Lewis acid catalysis is possible. Sigmatropic reactions often have transition-metal catalysts that form intermediates in analogous reactions. The most well-known of the sigmatropic rearrangements are the ,3Cope rearrangement, Claisen rearrangement, Carroll rearrangement, and the Fischer indole synthesis. Overview of sigmatropic shifts Woodward–Hoffman sigmatropic shift nomenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sigmatropic Rearrangements
A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one σ-bond is changed to another σ-bond in an uncatalyzed intramolecular reaction. The name ''sigmatropic'' is the result of a compounding of the long-established sigma designation from single carbon–carbon bonds and the Greek word ''tropos'', meaning turn. In this type of rearrangement reaction, a substituent moves from one part of a π-bonded system to another part in an intramolecular reaction with simultaneous rearrangement of the π system. True sigmatropic reactions are usually uncatalyzed, although Lewis acid catalysis is possible. Sigmatropic reactions often have transition-metal catalysts that form intermediates in analogous reactions. The most well-known of the sigmatropic rearrangements are the ,3Cope rearrangement, Claisen rearrangement, Carroll rearrangement, and the Fischer indole synthesis. Overview of sigmatropic shifts Woodward–Hoffman sigmatropic shift nomenclatu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Claisen Rearrangement
The Claisen rearrangement is a powerful carbon–carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl vinyl ether will initiate a ,3sigmatropic rearrangement to give a γ,δ-unsaturated carbonyl, driven by exergonically favored carbonyl CO bond formation (ΔΔHf = -327kcalmol−1). Mechanism The Claisen rearrangement is an exothermic, concerted (bond cleavage and recombination) pericyclic reaction. Woodward–Hoffmann rules show a suprafacial, stereospecific reaction pathway. The kinetics are of the first order and the whole transformation proceeds through a highly ordered cyclic transition state and is intramolecular. Crossover experiments eliminate the possibility of the rearrangement occurring via an intermolecular reaction mechanism and are consistent with an intramolecular process. There are substantial solvent effects observed in the Claisen rearrangement, where polar solvents tend to accelerate the reaction to a greater e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Woodward–Hoffmann Rules
The Woodward–Hoffmann rules (or the pericyclic selection rules), devised by Robert Burns Woodward and Roald Hoffmann, are a set of rules used to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions, an important class of reactions in organic chemistry. The rules are best understood in terms of the concept of ''the conservation of orbital symmetry'' using ''orbital correlation diagrams'' (see Section 3 below). The Woodward–Hoffmann rules are a consequence of the changes in electronic structure that occur during a pericyclic reaction and are predicated on the phasing of the interacting molecular orbitals. They are applicable to all classes of pericyclic reactions (and their microscopic reverse 'retro' processes), including (1) electrocyclic reaction, electrocyclizations, (2) cycloadditions, (3) sigmatropic reactions, (4) group transfer reactions, (5) ene reactions, (6) cheletropic reactions, and (7) dyotropic reactions. Due to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rearrangement Reaction
In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular. In the example below, the substituent R moves from carbon atom 1 to carbon atom 2: :\underset\ce\ce\underset\ce\ce Intermolecular rearrangements also take place. A rearrangement is not well represented by simple and discrete electron transfers (represented by curved arrows in organic chemistry texts). The actual mechanism of alkyl groups moving, as in Wagner-Meerwein rearrangement, probably involves transfer of the moving alkyl group fluidly along a bond, not ionic bond-breaking and forming. In pericyclic reactions, explanation by orbital interactions give a better picture than simple discrete electron transfers. It is, nevertheless, possible to draw the curv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cope Rearrangement
The Cope rearrangement is an extensively studied organic reaction involving the ,3sigmatropic rearrangement of 1,5-dienes. It was developed by Arthur C. Cope and Elizabeth Hardy. For example, 3-methyl-hexa-1,5-diene heated to 300 °C yields hepta-1,5-diene. The Cope rearrangement causes the fluxional states of the molecules in the bullvalene family. Mechanism The Cope rearrangement is the prototypical example of a concerted sigmatropic rearrangement. It is classified as a ,3sigmatropic rearrangement with the Woodward–Hoffmann symbol π2s+σ2s+π2s.html" ;"title="sub>π2s+σ2s+π2s">sub>π2s+σ2s+π2sand is therefore thermally allowed. It is sometimes useful to think of it as going through a transition state energetically and structurally equivalent to a diradical, although the diradical is not usually a true intermediate (potential energy minimum). The chair transition state illustrated here is preferred in open-chain systems (as shown by the Doering-Roth experiments ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pericyclic Reaction
In organic chemistry, a pericyclic reaction is the type of organic reaction wherein the transition state of the molecule has a cyclic geometry, the reaction progresses in a concerted fashion, and the bond orbitals involved in the reaction overlap in a continuous cycle at the transition state. Pericyclic reactions stand in contrast to ''linear reactions'', encompassing most organic transformations and proceeding through an acyclic transition state, on the one hand and '' coarctate reactions'', which proceed through a doubly cyclic, concerted transition state on the other hand. Pericyclic reactions are usually rearrangement or addition reactions. The major classes of pericyclic reactions are given in the table below (the three most important classes are shown in bold). Ene reactions and cheletropic reactions are often classed as group transfer reactions and cycloadditions/cycloeliminations, respectively, while dyotropic reactions and group transfer reactions (if ene reactions are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roald Hoffmann
Roald Hoffmann (born Roald Safran; July 18, 1937) is a Polish Americans, Polish-American theoretical chemistry, theoretical chemist who won the 1981 Nobel Prize in Chemistry. He has also published plays and poetry. He is the Frank H. T. Rhodes Professor of Humane Letters, Emeritus, at Cornell University, in Ithaca, New York. Early life Escape from the Holocaust Hoffmann was born in Złoczów, Second Polish Republic (now Zolochiv, Ukraine), to a Polish-Jewish family, and was named in honor of the Norway, Norwegian explorer Roald Amundsen. His parents were Clara (Rosen), a teacher, and Hillel Safran, a civil engineer. After Germany invaded Poland and occupied the town, his family was placed in a labor camp where his father, who was familiar with much of the local infrastructure, was a valued prisoner. As the situation grew more dangerous, with prisoners being transferred to extermination camps, the family bribed guards to allow an escape. They arranged with a Ukrainian neighbor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert Burns Woodward
Robert Burns Woodward (April 10, 1917 – July 8, 1979) was an American organic chemist. He is considered by many to be the most preeminent synthetic organic chemist of the twentieth century, having made many key contributions to the subject, especially in the synthesis of complex natural products and the determination of their molecular structure. He also worked closely with Roald Hoffmann on theoretical studies of chemical reactions. He was awarded the Nobel Prize in Chemistry in 1965. Early life and education Woodward was born in Boston, Massachusetts, on April 10, 1917. He was the son of Margaret Burns (an immigrant from Scotland who claimed to be a descendant of the poet, Robert Burns) and her husband, Arthur Chester Woodward, himself the son of Roxbury apothecary, Harlow Elliot Woodward. His father was one of the many victims of the 1918 influenza pandemic of 1918. From a very early age, Woodward was attracted to and engaged in private study of chemistry while he att ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Woodward Hoffmann Order Nomenclature Bond Break
A woodward is a warden of a wood. Woodward may also refer to: Places ;United States * Woodward, Iowa * Woodward, Oklahoma * Woodward, Pennsylvania, a census-designated place * Woodward Avenue, a street in Tallahassee, Florida, which bisects the campus of Florida State University * Woodward Avenue, a Michigan state highway * Woodward Corridor, a neighborhood in Detroit, Michigan * Woodward County, Oklahoma * Woodward Park (other), multiple places * Woodward Pond, a man-made pond in Bowie, Maryland * Woodward Township, Pennsylvania (other), multiple places People * Woodward (surname) * Frank Lee Woodward (1871–1952), English educationist, Pali scholar, author and theosophist Businesses * Woodward, Inc., American maker of energy devices * Woodward & Lothrop, American department store chain * Woodward Iron Company, in Birmingham (Woodward) Alabama * Woodward's, Canadian department store chain ** The Woodward's building in Vancouver, British Columbia Educatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which by definition have the same molecular formula and sequence of bonded atoms (constitution), but differ in structural formula (the three-dimensional orientations of their atoms in space). For this reason, it is also known as 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question ( dynamic stereochemis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereochemistry Rentention Inversion
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which by definition have the same molecular formula and sequence of bonded atoms (constitution), but differ in structural formula (the three-dimensional orientations of their atoms in space). For this reason, it is also known as 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question (dynamic stereochemistry) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Suprafacial Antarafacial -1,5-
Antarafacial ( Woodward-Hoffmann symbol a) and suprafacial (s) are two topological concepts in organic chemistry describing the relationship between two simultaneous chemical bond making and/or bond breaking processes in or around a reaction center. The reaction center can be a p- or sp''n-''orbital (Woodward-Hoffmann symbol ω), a conjugated system (π) or even a sigma bond (σ). * The relationship is ''antarafacial'' when opposite faces of the π system or isolated orbital are involved in the process (think ''anti''). For a σ bond, it corresponds to involvement of one "interior" lobe and one "exterior" lobe of the bond. * The relationship is ''suprafacial'' when the same face of the π system or isolated orbital are involved in the process (think ''syn''). For a σ bond, it corresponds to involvement of two "interior" lobes or two "exterior" lobes of the bond. The components of all pericyclic reactions, including sigmatropic reactions and cycloadditions, and electrocyclizatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
