AcharyaChanakya/simple-wikipedia huggingface dataset:
Several witnesses at the youth camp, believe (as of 23 July 2011) that there was more than one shooter. The police have received descriptions of a second gunman, and are currently checking this information. Due to the uncertainty surrounding these witness descriptions and the chaotic nature of the events the police have, as a matter of precaution, yet to make an official comment on the matter. Acting Police Chief Sveinung Sponheim has said that "It's very difficult at this point to say whether he was acting alone or whether he was acting as part of a larger network".
At a press conference on the morning after the attacks, prime minister Jens Stoltenberg called the attack a "national tragedy" and the worst atrocity since World War II. Stoltenberg said that the attack would not hurt the Norwegian democracy, and said the proper answer to the violence was "more democracy, more openness, but not naivety".
Eskil Pedersen of the Workers' Youth League vowed to "return to Utøya" and urged Norway to continue its tradition of openness and tolerance.
King Harald sent his condolences to the victims and their families, and urged unity.
Svein Østerud , professor emeritus, said that before we can analyze the trauma of the nation, we have to acknowledge that Breivik and [some] other terrorists, are youths that lost their way, when going thru institutions ... while struggling to find one's identity, and at the same time (and everyday) being forced to [ conform to the] norms set by school, parents, and social media.
The European Union, NATO, the United Nations Security Council, governments and leaders from around the world expressed their condemnation of the attack, condolences, and solidarity with Norway.
At Utøya, the place of memorial is called ["the clearing"] "Lysninga"; a part of it is ["the ring"] "Ringen" - a "ring of steel [that] hangs between trees and here the names and age of the majority of those 69 killed are engraved"; "it lies at the highest point of the island"; It was unveiled during the summer of 2015. "Hegnhuset" was inaugurated in 2016.
A temporary national monument in Oslo was unveiled on 22 July 2016.
One monolith stands in each municipality.
At 53 [places] in Norway, are statues by Nico Widerberg that were anonymously financed.
One monolith was put at Utsikten - a roadside rest area with a view of Utøya; it is located on E16 at Nes in Hole (municipality).
In June 2017 the government decided that one of the national memorials, should be placed at Utøya-kaia, in Hole municipality; the memorial will not [be a work of art, or] have an artistic expression. KORO , an agency under the Ministry of Culture, will no longer formally be tied to the process in regard to the memorial in Hole.
Jan Kjærstad published in 2017, "Berge", a novel that is about the attacks and a triple homicide in 1999, in Norway .
Harald Cerny
Harald Cerny (born 13 September 1973) is a former Austrian football midfielder. He played mostly for TSV 1860 München.
He started his career with ASV Hinterbrühl and FC Admira/Wacker where he played in the different youth teams. At the age of 19 he went to Bayern München where he started the professional career. The first two years he played for the second squad but in the 1992/93 he played in the first team giving his debut versus Eintracht Frankfurt. 1993 he went back to Austria playing with FC Admira/Wacker . After Wacker Innsbruck in the 1994/95 season he went back to Munich but played for Bayerns rival TSV 1860 München. With 268 matches, 238 of them in the Bundesliga, for 1860 he is the record holder of the club. Due to injuries, he ended his career in 2007.
Cerny made his debut for Austria in March 1993 against Greece. He played 47 matches and scored four goals.His last international was an April 2004 against Luxembourg. He was also in the squad for the 1998 FIFA World Cup in France. There he played two matches versus Cameroon and Chile.
Franz Wohlfahrt
Franz Bernhard Wohlfahrt (born 1 July 1964 in Sankt Veit an der Glan, Austria) is a former Austrian goalkeeper.
He started with the local club SV St.Veit and turned professional with F.K. Austria Wien. He came together with his older brother Mario, who soon went back to St. Veit. Franz Wohlfahrt played then 20 years or 496 matches for this club divided in two sections. With Austria Wien he became 6 times Austrian Champion and four times Austrian cup winner. He became widely known during a UEFA Cup match versus Ajax Amsterdam when he was injured by a bar thrown by an Ajax supporter. Following this Ajax was banned for one year in European football. From 1996 till 2000 he played for the German team VfB Stuttgart, with the club he played in the 1997/98 UEFA Cup final versus Chelsea (0:1). 2000 he went back to Austria Wien. 2002 he ended his career but in 2007 he started again playing for ASK Hirm, whose goalkeeper was injured.
In 1983 he played in the 1983 FIFA World Youth Championship. His first match in the senior team was in August 1987 in a match versus Switzerland. His last match was a qualification match for the 2002 FIFA World Cup versus Turkey. He was also a goalkeeper in the 1998 FIFA World Cup squad. In 1999 he was goalkeeper during the 0:9 defeat versus Spain in Valencia. All in all he played 59 matches for Austria.
Gas exchange
Exchange of gases or gas exchange is carried out by organisms, where different gases move in different directions. Animals, microorganisms and plants breathe out carbon dioxide and breathe in oxygen. To balance the composition of air, plants use carbon dioxide to carry out photosynthesis, so oxygen is made. Plants only carry this out during the day, when there is sunlight. Plants respire all day and night.
In humans, gas exchange happens in the alveolus (alveoli for plural). These are in the lungs and help with diffusion. Oxygen diffuses into the bloodstream, from the air. Oxygen is used in aerobic respiration. Carbon dioxide diffuses out of the bloodstream, into the air. Carbon dioxide is a waste product made by respiration.
Not all of the oxygen breathed in gets to the blood. A small percentage is breathed back out again, and a small amount of carbon dioxide stays in the blood.
Pentene
Pentene is the name of alkenes with the formula CH. They are hydrocarbons. In total, there are five different pentenes. Pentens occur in cracking processes and in natural gas. Pentenes are used for polymerization, and for the synthesis of isoprene, amyl alcohols and Alkylphenols. Amyl alcohols are used as stabilizers in the production of Chloroform and Dichloromethane to stop phosgene from being made.
Paul Strzelecki
Paul Edmund de Strzelecki (20 July 1797 — October 1873) was a Polish man who taught himself geology. He became famous for his explorations in Australia.
He was born in Gluszyna, near Poznan, Western Poland in 1797 and later served briefly with the Prussian army. He tried unsuccessfully to marry a young girl, and then was accused of stealing money from his employer. He moved to London and gave himself the title of Count Strzelecki. In 1834 he went to North America and spent time visiting mineral areas and exploring for minerals. He is said to be the first person to find copper in Canada. In 1836 he travelled along the west coast from Chile to California.
In 1839 he visited the Hawaii, Tahiti, New Zealand and finally landed in Sydney, Australia. He wanted to make a geological map, and explored large parts of New South Wales and Victoria, including the Australian Alps. He climbed Australia's highest mountain, and named it Mount Kosciuszko, after the Polish leader, Tadeusz Kosciuszko.
He spent several years in Tasmania before going back to Sydney. He went back to London in 1843. He wrote a book on his discoveries in Australia called "Physical Description of New South Wales and Van Diemen's Land". He was given the Founder's Medal by the Royal Geographical Society.
In 1847—8 he was put in charge of the giving out money in Ireland during the Great Famine for the British Relief Association. He established standards for giving out assistance that are still being used.
He was made a Fellow of the Royal Geographic Society and the Royal Society. He was awarded the K.C.M.G. in 1869. He died from cancer in 1873. He left instructions that after his death his papers were to be burnt and his body buried in an unmarked grave.
A road from Lyndhurst to Innamincka was named the Strzelecki Track after Paul Strzelecki. It was used until the 1930's to move cattle to Adelaide, and now is the main road to Moomba, a huge natural gas field which supplies Adelaide and Sydney. The Strzelecki Ranges in Victoria are also named after him. A large national park on Flinders Island, the Strzelecki National Park, was named after Strzelecki who climbed the mountains there in 1842.
Stress (mechanics)
Stress is the force per unit area on a body that tends to cause it to change shape.
Stress is a measure of the internal forces in a body between its particles. These internal forces are a reaction to the external forces applied on the body that cause it to separate, compress or slide. External forces are either surface forces or body forces. Stress is the average force per unit area that a particle of a body exerts on an adjacent particle, across an imaginary surface that separates them.
The formula for uniaxial normal stress is:
where σ is the stress, F is the force and A is the surface area.
In SI units, force is measured in newtons and area in square metres. This means stress is newtons per square meter, or N/m. However, stress has its own SI unit, called the pascal. 1 pascal (symbol Pa) is equal to 1 N/m. In Imperial units, stress is measured in pound-force per square inch, which is often shortened to "psi". The dimension of stress is the same as that of pressure.
In continuum mechanics, the loaded deformable body behaves as a continuum. So, these internal forces are distributed continually within the volume of the material body. (This means that the stress distribution in the body is expressed as a piecewise continuous function of space and time.) The forces cause deformation of the body's shape. The deformation can lead to a permanent shape change or structural failure if the material is not strong enough.
Some models of continuum mechanics treat force as something that can change. Other models look at the deformation of matter and solid bodies, because the characteristics of matter and solids are three dimensional. Each approach can give different results. Classical models of continuum mechanics assume an average force and do not properly include "geometrical factors". (The geometry of the body can be important to how stress is shared out and how energy builds up during the application of the external force.)
In some situations, the stress within an object can be described by a single number, or by a single vector (a number and a direction). Three such simple stress situations are the "uniaxial normal stress", the "simple shear stress", and the "isotropic normal stress".
Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress.
Therefore in a uniaxial material the length increases in the tensile stress direction and the other two directions will decrease in size. In the uniaxial manner of tension, tensile stress is induced by pulling forces. Tensile stress is the opposite of compressive stress.
Structural members in direct tension are ropes, soil anchors and nails, bolts, etc. Beams subjected to bending moments may include tensile stress as well as compressive stress and/or shear stress.
Tensile stress may be increased until the reach of tensile strength, namely the "limit state" of stress.
All real objects occupy three-dimensional space. However, if two dimensions are very large or very small compared to the others, the object may be modelled as one-dimensional. This simplifies the mathematical modelling of the object. One-dimensional objects include a piece of wire loaded at the ends and viewed from the side, and a metal sheet loaded on the face and viewed up close and through the cross section.
Pericyclic reaction
In organic chemistry, a pericyclic reaction is a type of chemical reaction between organic compounds. In the case of pericyclic reactions, the transition state of the molecule is a ring (has a cyclic geometry), and the reaction goes forward in a concerted way. Pericyclic reactions are usually rearrangement reactions. The most important groups of pericyclic reactions are:
In general, pericyclic reactions are equilibrium processes. However, it is possible to push the reaction in one direction if the product is at a significantly lower energy level. This is applying Le Chatelier's principle to a reaction involving a single molecule.
Many pericyclic reactions have similar stepwise radical processes connected with them. Chemists disagree whether some reactions are pericyclic reactions. For example, it is not definitively known whether the [2+2] cycloaddition mechanism is concerted (or may depend on the reactive system). Many pericyclic reactions have similar reactions that are metal-catalyzed. But these metal-catalyzed reactions are also not really pericyclic. The metal catalysts stabilize the reaction intermediates. So the reaction is not concerted, but rather metal-stabilized.
A large photoinduced hydrogen sigmatropic shift was utilized in a corrin synthesis performed by Albert Eschenmoser containing a 16π system.
Due to the principle of microscopic reversibility, there is a parallel set of "retro" pericyclic reactions, which perform the reverse reaction.
Pericyclic reactions also happen in several biological processes:
2011–12 Manchester United F.C. season
The 2011–12 season is Manchester United's 20th season in the Premier League.
Manchester United signed a £40 million four-year deal with DHL.
In November, Sir Alex Ferguson celebrated 25 years in charge of the club.
Manchester United started their season with a tour in the United States. United finishing the tour with a game against Barcelona in Washington on 30 July.
Manchester United will face Benfica, Basel and Otelul Galati in Group C.
Manchester United were drawn against Crystal Palace in the quarter-finals of the League Cup.
The Annoying Orange
The Annoying Orange is a comedy web series created by Dane Boedigheimer. The main character is an orange who annoys other fruits. The episodes are uploaded to the YouTube channel "realannoyingorange" weekly, with now over 200 videos. , The channel had almost 3 million subcribers. At that time, it was 43rd in terms of how many people are subscribed to it.
Orange is the main character. He is described as really annoying, but sometimes funny. He warns others about a knife and other items ready to kill them.
Pear is described as a normal/bad/lying/negative/abusive character. He was Orange (Annoying Orange)'s best friend and normally tells Orange to stop being annoying and shut up, but it is discovered in the episode "Wishful Thinking" that Pear would not be friends without Grapefruit. Pear is in Grapefruit's gang and was making fun of Orange.
Midget Apple is a small apple in the series. He does not like being called "Midget Apple", prefering the term "Little Apple".
Apple is Orange's former best friend and current rival (bully). Apple is in Grapefruit's bullying gang.
In 2012, Cartoon Network made a 2012-2014 high fructose adventures TV show based on the YouTube series.
Cycloaddition
A cycloaddition is a chemical reaction between reactants with double bonds that get replaced by a ring structure. It is a pericyclic chemical reaction where "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." It is a cyclization reaction: it makes new ring of atoms.
Cycloadditions are named by the basic size of the molecules that are being brought together. This would make the Diels–Alder reaction a [4 + 2]cycloaddition, and the 1,3-dipolar cycloaddition a [3 + 2]cycloaddition. This type of reaction is a non-polar addition reaction.
Heat can cause the double bonds to form a ring. Thermal cycloadditions usually have (4n + 2) π electrons participating in the starting material, for some whole number "n". Because of orbital symmetry, most cycloadditions are suprafacial-suprafacial. Rarely, they are antarafacial-antarafacial. There are a few examples of thermal cycloadditions which have 4n π electrons (for example the [2 + 2] cycloaddition). These proceed in a suprafacial-antarafacial sense. For example, the dimerisation of ketene has a orthogonal set of p orbitals. Those p orbitals allow the reaction to proceed using a crossed transition state.
Light can also cause the double bonds to form a ring. Cycloadditions in which 4n π electrons participate can also occur as a result of photochemical activation. Here, one component makes an electron move from the highest occupied molecular orbital (HOMO) (π bonding) to the lowest unoccupied molecular orbital (LUMO) (π* antibonding). After the electron is promoted to the higher orbital, orbital symmetry allows the reaction to proceed in a suprafacial-suprafacial manner. An example is the DeMayo reaction. Another example is shown below, the photochemical dimerization of cinnamic acid.
Note that not all photochemical (2+2) cyclizations are cycloadditions; some are known to operate by radical mechanisms.
Some cycloadditions instead of π bonds operate through strained cyclopropane rings; as these have significant π character. For example, an analog for the Diels–Alder reaction is the quadricyclane-DMAD reaction:
In the (i+j+...) cycloaddition notation i and j refer to the number of atoms involved in the cycloaddition. In this notation a Diels-Alder reaction is a (4+2)cycloaddition and a 1,3-dipolar addition such as the first step in ozonolysis is a (3+2)cycloaddition. This notation uses parenthesis. The IUPAC preferred notation however, with [i+j+...] counts electrons and not atoms. It uses square brackets. In this notation, the Diels–Alder reaction and the dipolar reaction both become a [4+2]cycloaddition. The reaction between norbornadiene and an activated alkyne is a [2+2+2]cycloaddition.
The Diels–Alder reaction is a [4+2]cycloaddition reaction.
The Huisgen cycloaddition reaction is a [2+3]cycloaddition.
The Nitrone-olefin cycloaddition is a [3+2]cycloaddition.
Cycloadditions often have metal-catalyzed and stepwise radical analogs, however these are not strictly speaking pericyclic reactions. When charged or radical intermediates are involved in a cycloaddition, or when the cycloaddition result is found in a series of reaction steps, they are sometimes called formal cycloadditions to make a difference from true pericyclic cycloadditions.
One example of a formal [3+3]cycloaddition between a cyclic enone and an enamine catalyzed by "n"-butyllithium is a Stork enamine / 1,2-addition cascade reaction:
Cheletropic reaction
A cheletropic reaction is a type of pericyclic reaction where one atom on one of the reagents gets two new bonds. A pericyclic reaction is one that involves a transition state with a cyclic array of atoms and an associated cyclic array of interacting orbitals. A reorganization of σ and π bonds occurs in this cyclic array.
Cheletropic reactions are a subclass of cycloadditions. What sets cheletropic reactions apart is that on one of the reagents, both new bonds are being made to the same atom. A few examples are shown to the right in Figure 1. In the first case, the single atom is the carbon atom in the carbonyl group. That carbon atom ends up in carbon monoxide. The end result is making two new bonds to one atom. The first two examples are known as "cheletropic extrusions" because a small stable molecule is given off in the reaction. The driving force for these reactions is often the entropic benefit of releasing a gas (e.g. CO or N).
Because of the geometry of the molecules involved in cheletropic reactions, they confirm a number of predictions made by theoretical chemists. Cheletropic reactions confirm the conservation of molecular orbital symmetry.
In the pericyclic transition state, a small molecule donates two electrons to the ring. Two possible geometries can explain the reaction. The small molecule can approach in either a linear or non-linear way. In the linear approach, the electrons in the orbital of the small molecule are pointed directly at the π system of the big molecule. In the non-linear approach, the orbital approaches at a slightly off angle. The π-systems ability to rotate as the small molecule approaches is crucial in forming new bonds. The direction of rotation will be different depending on how many π-electrons are in the system. A diagram of a two-electron fragment approaching a four-electron π-system using frontier molecular orbitals is shown below. The rotation will be disrotatory if the small molecule approaches linearly and conrotatory if the molecule approaches non-linearly. Disrotatory and conrotatory tell how the bonds in the π-system are rotating. Disrotatory means opposite directions while conrotatory means the same direction. This is also shown in the diagram below.
Using Huckel's Rule, one can tell if the π-system is aromatic or anti-aromatic. If aromatic, linear approaches use disrotatory motion while non-linear approaches use conrotatory motion. The opposite goes with an anti-aromatic system. Linear approaches will have conrotatory motion while non-linear approaches will have disrotatory motion.
When sulfur dioxide reacts with butadiene and isoprene, two different products result. The reaction mechanism will control what gets made. A kinetic product and a thermodynamic product are both possible. More of the thermodynamic product gets made than the kinetic product. The kinetic product comes from a Diels–Alder reaction, while a cheletropic reaction makes a more thermodynamically stable product. The cheletropic pathway is used more because it makes to a more stable five-membered ring adduct. The scheme below shows the difference between the two products. The path to the left shows the thermodynamic product, while the path to the right shows the kinetic product. Suarez and Sordo showed this in 1995. They showed this both with experiments and using Gaussian calculations.
One example of this is the cheletropic reactions of 1,3-dienes with sulfur dioxide. Chemists have carefully looked at the kinetics of this reaction. In 1976, Isaacs and Laila measured the kenetic factors for the addition of sulfur dioxide to butadiene derivatives. Rates of addition were monitored in benzene at 30 °C with an initial twentyfold excess of diene. They used a spectrophotometer to study light at 320 nm to measure the disappearance of SO. The reaction showed "pseudo first-order kinetics". The chemists found that electron-withdrawing groups on the diene decreased the rate of reaction. Also, the reaction rate was affected considerably by steric effects of 2-substituents, with more bulky groups increasing the rate of reaction. (In other words, the larger the group of atoms hanging from the second carbon atom, the quicker the reaction ran.) The authors attribute this to the tendency of bulky groups to favor the cisoid conformation of the diene which is essential to the reaction (see table below). In addition, the rates at four temperatures were measured for seven of the dienes. From these measurements, chemists used the Arrhenius equation to calculate the enthalpy of activation (ΔH) and entropy of activation (ΔS) for each reaction. This was one of the first important efforts to study the kenetics of a cheletropic reaction.
Monnat, Vogel, and Sordo, in 2002, measured the kinetics of addition of sulfur dioxide to 1,2-dimethylidenecycloalkanes. They wrote that the reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide can give two different products depending on reaction conditions. The reaction makes the corresponding sultine through a hetero-Diels-Alder reaction under kinetic control (≤ -60 °C), but, under thermodynamic control (≥ -40 °C), the reaction makes the corresponding sulfolene through a cheletropic reaction. The activation enthalpy for the hetero-Diels-Alder reaction is about 2 kcal/mol smaller than that for the corresponding cheletropic reaction. The sulfolene is about 10 kcal/mol more stable than the isometric sultine in CHCl/SO solution.
The authors were able to experimentally work out a rate law at 261.2 K for the reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide to give the corresponding sulfolene. The reaction was first order in 1,2-dimethylidenecyclohexane but second order in sulfur dioxide (see below). This confirmed a prediction of theoretical chemists based on high-level "ab initio" quantum calculations. Using computational methods, the authors proposed a transition structure for the cheletropic reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide (see figure at right). The reaction is second order in sulfur dioxide because another molecule of sulfur dioxide likely binds to the transition state to help stabilize it. Similar results were found in an 1995 study by Suarez, Sordo, and Sordo which used "ab initio" calculations to study the kinetic and thermodynamic control of the reaction of sulfur dioxide with 1,3-dienes.
The effect of the solvent of the cheletropic reaction of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide (shown at right) was kinetically investigated in 14 solvents. The reaction rate constants of the forward and reverse reaction in addition to the equilibrium constants were found to be linearly correlated with the E(30) solvent polarity scale.
Reactions were done at 120 °C and were studied by 1H-NMR spectroscopy of the reaction mixture. The forward rate k was found to decrease by a factor of 4.5 going from cyclohexane to methanol. The reverse rate k was found to increase by a factor of 53 going from cyclohexane to methanol, while the equilibrium constant K decreased by a factor of 140. It is suggested that there is a change of the polarity during the activation process as evidenced by relationships between the equilibrium and kinetic data. The authors say that the reaction appears to be influenced by the polarity of the solvent, and this can be shown by the change in the dipole moments when going from reactant to transition state to product. The authors also state that the cheletropic reaction doesn’t seem to be influenced by either solvent acidity or basicity.
The results of this study lead the authors to expect the following behaviors:
1. The change in the solvent polarity will influence the rate less than the equilibrium.
2. The rate constants will be characterized by opposite effect on the polarity: k will slightly decrease with the increase of E(30), and k will increase under the same conditions.
3. The effect on k will be larger than on k.
One of the most synthetically important cheletropic reactions is the addition of a singlet carbene to an alkene to make a cyclopropane (see figure at left). A carbene is a neutral molecule containing a divalent carbon with six electrons in its valence shell. Because of this, carbenes are highly reactive electrophiles and generated as reaction intermediates. A singlet carbene contains an empty "p" orbital and a roughly "sp" hybrid orbital that has two electrons. Singlet carbenes add stereospecifically to alkenes, and alkene stereochemistry is retained in the cyclopropane product. The mechanism for addition of a carbene to an alkene is a concerted [2+1] cycloaddition (see figure). Carbenes derived from chloroform or bromoform can be used to add CX to an alkene to give a dihalocyclopropane, while the Simmons-Smith reagent adds CH.
Interaction of the filled carbene orbital with the alkene π system creates a four-electron system and favors a non-linear approach. It is also favorable to mix the carbene empty "p" orbital with the filled alkene π orbital. Favorable mixing occurs through a non-linear approach (see figure 2 at right). However, while theory clearly favors a non-linear approach, there are no obvious experimental implications for a linear vs. non-linear approach.
Sigmatropic reaction
A sigmatropic reaction in organic chemistry is a pericyclic reaction. A sigmatropic reaction does not use a catalyst and involves a single molecule (an uncatalyzed intramolecular process). It changes one σ-bond into a different σ-bond. The name "sigmatropic" is the result of a compounding of the long-established "sigma" name for single carbon-carbon bonds and the Greek word "tropos", meaning turn. This is a rearrangement reaction which means that the bonds in a molecule shift between atoms without any atoms leaving or new atoms added to the molecule. In a sigmatropic 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 usually do not need a catalyst. Some sigmatropic reactions are catalyzed by a Lewis acid. Sigmatropic reactions often have transition-metal catalysts that form intermediates in analogous reactions. The most well-known of the sigmatropic rearrangements are the [3,3] Cope rearrangement, Claisen rearrangement, Carroll rearrangement and the Fischer indole synthesis.
A special notation is used to describe sigmatropic shifts. Each of the carbon atoms on the backbone of the molecule are assigned a position number. Sigmatropic rearrangements are described by an order term [i,j]. This means the migration of a σ-bond adjacent to one or more π systems to a new position (i-1) and (j-1) atoms removed from the original location of the σ-bond. When the sum of i and j is an even number, this is an indication of the involvement of a neutral, all C atom chain. An odd number suggests that there is a charged C atom or of a heteroatom lone pair replacing a carbon-carbon double bond. Thus, [1,5] and [3,3] shifts become [1,4] and [2,3] shifts with heteroatoms, while preserving symmetry considerations. Hydrogens are omitted in the third example for clarity.
Here is a way to find the order of a given sigmatropic rearrangement. The first step is to give numbers to each atom starting with the atoms of the bond being broken as atom 1. Chemists count the atoms in each direction from the broken bond to the atoms that form the new σ-bond in the product. The numbers that correspond to the atoms forming the new bond are then separated by a comma and placed within brackets. This creates the sigmatropic reaction order descriptor.
Chemists also count atoms when naming a sigmatropic shift where a hydrogen atom moves. The carbon chain does not break in a hydrogen atom migration. So, chemists count across all atoms involved in the reaction rather than only across the closest atoms. For example, the following hydrogen atom migration is of order [1,5], attained by counting counterclockwise through the π system, rather than the [1,3] order through the ring CH group that would mistakenly result if counted clockwise.
Chemists have studied sigmatropic reactions where the migrating group has a sterocenter. In principle, all sigmatropic shifts can occur with either the same (retention) or the opposite (inversion) geometry of the migrating group. This depends on whether the original bonding lobe of the migrating atom or its other lobe is used to form the new bond.
In cases of stereochemical retention, the migrating group translates without rotation into the bonding position. In the case of stereochemical inversion the migrating group both rotates and translates to reach its bonded conformation.
There is another way that a sigmatropic reaction can produce products with different sterochemistry. The migrating group can stay on the original face of the π system after rebonding. Or, it can go to the opposite face of the π system. If the migrating group remains on the same face of the π system, the shift is known as suprafacial. If the migrating group transfers to the opposite face is called an antarafacial shift. Transformations that occur within small- or medium-sized rings cannot make antarafacial shifts.
In a thermal [1,3] hydride shift, a hydride moves three atoms. The Woodward-Hoffmann rules dictate that it would proceed in an antarafacial shift. Although such a shift is symmetry allowed, the Mobius topology required in the transition state prohibits such a shift. It is geometrically impossible. This is why enols do not isomerize without an acid or base catalyst.
Thermal alkyl [1,3] shifts, similar to [1,3] hydride shifts, must proceed antarafacially. The geometry of the transition state is prohibitive. But an alkyl group, due to the nature of its orbitals, can invert its geometry and form a new bond with the back lobe of its sp orbital. This reaction will result a suprafacial shift. These reactions are still not common in open chain systems because of the highly ordered nature of the transition state. So, the reactions work better in cyclic molecules.
Photochemical [1,3] shifts should be suprafacial shifts; however, most are non-concerted because they proceed through a triplet state (that is, they have a diradical mechanism, to which the Woodward-Hoffmann rules do not apply).
A [1,5] shift involves the shift of 1 substituent (-H, -R or -Ar) down 5 atoms of a π system. Hydrogen has been shown to shift in both cyclic and open chain systems at temperatures at or above 200 ˚C. These reactions are predicted to proceed suprafacially, by a Huckel-topology transition state.
Photoirradiation would require an antarafacial shift of hydrogen. Although such reactions are rare, there are examples where antarafacial shifts are favored:
In contrast to hydrogen [1,5] shifts, there have never been any observed [1,5] alky shifts in an open-chain system. Chemists have determined rate preferences for [1,5] alkyl shifts in cyclic systems: carbonyl and carboxyl> hydride> phenyl and vinyl» alkyl.
Alkyl groups undergo [1,5] shifts very poorly and usually require high temperatures. However, for cyclohexadienes, the temperature for alkyl shifts is not much higher than that for carbonyls, the best migratory group. A study showed that this is because alkyl shifts on cyclohexadienes proceed through a different mechanism. First the ring opens, followed by a [1,7] shift, and then the ring reforms electrocyclically:
This same mechanistic process is seen below, without the final electrocyclic ring-closing reaction, in the interconversion of lumisterol to vitamin D.
[1,7] sigmatropic shifts are predicted by the Woodward-Hoffmann rules to proceed in an antarafacial fashion, by a Mobius topology transition state. An antarafacial [1,7] shift is observed in the conversion of lumisterol to vitamin D, where following an electrocyclic ring opening to previtamin D, a methyl hydrogen shifts.
Bicyclic nonatrienes also undergo [1,7] shifts in a so called walk rearrangement, which is the shift of divalent group, as part of a three-membered ring, in a bicyclic molecule.
[3,3] sigmatropic shifts are well studied sigmatropic rearrangements. The Woodward-Hoffman rules predict that these six electron reactions would proceed suprafacially, using a Huckel topology transition state.
Discovered in 1912 by Rainer Ludwig Claisen, the Claisen rearrangement is the first recorded example of a [3,3]-sigmatropic rearrangement. This rearrangement is a useful carbon-carbon bond-forming reaction. An example of Claisen rearrangement is the [3,3] rearrangement of an allyl vinyl ether, which upon heating yields a γ,δ-unsaturated carbonyl. The formation of a carbonyl group makes this reaction, unlike other sigmatropic rearrangements, inherently irreversible.
The ortho-Claisen rearrangement involves the [3,3] shift of an allyl phenyl ether to an intermediate which quickly tautomerizes to an ortho-substituted phenol.
When both the ortho positions on the benzene ring are blocked, a second ortho-Claisen rearrangement will occur. This para-Claisen rearrangement ends with the tautomerization to a tri-substituted phenol.
The Cope rearrangement is an extensively studied organic reaction involving the [3,3] sigmatropic rearrangement of 1,5-dienes. It was developed by Arthur C. Cope. For example 3,4-dimethyl-1,5-hexadiene heated to 300 °C yields 2,6-octadiene.
The Oxy-Cope rearrangement a hydroxyl group is added at C3 forming an enal or enone after Keto-enol tautomerism of the intermediate enol:
The Carroll rearrangement is a rearrangement reaction in organic chemistry and involves the transformation of a β-keto allyl ester into a α-allyl-β-ketocarboxylic acid. This organic reaction can be followed by decarboxylation and the final product is a γ,δ-allylketone. The Carroll rearrangement is an adaptation of the Claisen rearrangement and effectively a decarboxylative allylation.
The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by Hermann Emil Fischer.
The choice of acid catalyst is very important. Successful acid catalysts include: Bronsted acids such as HCl, HSO, polyphosphoric acid and p-toluenesulfonic acid. Lewis acids such as boron trifluoride, zinc chloride, iron chloride, and aluminium chloride are also useful catalysts.
Similar to [3,3] shifts, the Woodward-Hoffman rules predict that [5,5] sigmatropic shifts would proceed suprafacially, Huckel topology transition state. These reactions are rarer than [3,3] sigmatropic shifts, but this is mainly a function of the fact that molecules that can undergo [5,5] shifts are rarer than molecules that can undergo [3,3] shifts.
The migration of a divalent group, such as O, S, NR or CR, which is part of a three-membered ring in a bicyclic molecule, is commonly referred to as a walk rearrangement. This can be formally characterized according to the Woodward-Hofmann rules as being a (1, n) sigmatropic shift. An example of such a rearrangement is the shift of substituents on tropilidenes (1,3,5-cycloheptatrienes). When heated, the pi-system goes through an electrocyclic ring closing to form bicycle[4,1,0]heptadiene (norcaradiene). Thereafter follows a [1,5] alkyl shift and an electrocyclic ring opening.
Proceeding through a [1,5] shift, the walk rearrangement of norcaradienes is expected to proceed suprafacially with a retention of stereochemistry. Experimental observations, however, show that the 1,5-shifts of norcaradienes proceed antarafacially. Theoretical calculations found the [1,5] shift to be a diradical process, but without involving any diradical minima on the potential energy surface.
Group transfer reaction
A Group transfer reaction is pericyclic reaction where one pi bond is converted to one sigma bond, at the same time that a sigma bond migrates.
Cadel Evans (born 14 February 1977 in Katherine, Northern Territory) is an Australian professional bicycle race driver. In 2011, he is the first Australian to win the Tour de France.
Cadel Evans was born on 14 February 1977 at the Katherine Hospital, Katherine, Northern Territory, Australia. He is the son of Helen Cocks, a bank manager and Paul Evans, a council foreman. He spent his early childhood in the small aboriginal community of Barunga, 80 km east of Katherine. At the age of seven, he was hit in the head by a horse and spent seven days in an induced coma. In 1986, his parents got divorced and he moved with his mother to Armidale, New South Wales. Later they moved to the state of Victoria. Skateboarding was one of his interests when he was a teenager. His father describes him as a good student, but otherwise just an ordinary kid who would leave his toys around. "Not in [my] wildest dreams" would he imagine that his son would become a top world athlete.
Evans attended Newling Public School in Armidale, and Eltham High School in Melbourne.
Grand Army Plaza (Manhattan)
Grand Army Plaza is at 59th Street and Fifth Avenue in Manhattan, New York. It is in front of the Plaza Hotel. It is opposite the southeast corner of Central Park. The sculptor Karl Bitter first had the idea for the Plaza in 1898. It is named after the Grand Army of the Potomac. The Carrère and Hastings architecture firm designed it. Construction was finished in 1916.
The Plaza is oval. 59th street divides it into northern and southern parts. The northern part has a golden statue of William Tecumseh Sherman designed by Augustus Saint-Gaudens. The statue features Sherman on a horse with the goddess "Victory" in front of him. There are often temporary sculpture exhibits at the north side of the plaza.
The southern part is the Plaza of the Pulitzer Fountain of Abundance. This fountain was designed by Bitter and paid for by Joseph Pulitzer. A bronze statue of the Roman goddess Pomona is at the top of the fountain. The statue of Pomona was the last one that Bitter designed.
The plaza was renovated in 1990 at a cost of $3.7 million. The Plaza Hotel is named for the Plaza, and is at its southwest corner.
USS Enterprise (CV-6)
USS "Enterprise" (CV-6), often called the "Big E," was the sixth aircraft carrier of the United States Navy. She was also the seventh U.S. Navy ship to use the name. She was launched in 1936 and was a "Yorktown" class aircraft carrier. She was one of three American carriers brought into service before World War II which survived the war. She took part in more fights against Japan than any other U.S. ship. These fights included the Battle of Midway, the Battle of the Eastern Solomons, the Battle of the Santa Cruz Islands, many other fights during the Guadalcanal campaign, the Battle of the Philippine Sea, and the Battle of Leyte Gulf. At three different times during the Pacific War, the Japanese said that she had been sunk in battle. This lead her to be nicknamed "The Grey Ghost".
"Enterprise" earned 20 battle stars. This was more than any other U.S. warship in World War II. Some have said that she is the most glorious and honored ship in the history of the United States Navy. However, the 18th century frigate USS "Constitution" could perhaps rival that.
"Enterprise" was launched on 3 October 1936 at Newport News Shipbuilding. She was sponsored by Lulie Swanson, who was the wife of the Secretary of the Navy Claude A. Swanson. "Enterprise" was commissioned on 12 May 1938. "Enterprise" sailed south so that her performance could be tested. This took her to Rio de Janeiro. After she returned, she was used along the east coast and in the Caribbean until April 1939. This is when she was ordered to serve in the Pacific.
"Enterprise" was one of fourteen ships to be fitted with the RCA CXAM-1 RADAR. She was first based in San Diego (where she was used in the movie "Dive Bomber") and then at Pearl Harbor after President Roosevelt ordered the Fleet to be based far forward. "Enterprise" and the aircraft squads she carries trained a lot and moved aircraft among the island bases of the Pacific. "Enterprise" left Pearl Harbor on 28 November 1941. "Enterprise" was completing a transport mission, returning to Hawaii after moving Marine Fighter Squadron 211 (VMF-211) to Wake Island on 7 December 1941. This was when the Japanese attacked Pearl Harbor.
"Enterprise" was returning to Oahu on the morning of 7 December 1941. 18 SBD Dauntlesses from "Enterprise" squadrons Scouting Squadron Six (VS-6) and Bombing Squadron Six (VB-6) arrived at Pearl Harbor while the Japanese were attacking it. Even though they were surprised, they quickly went into action to defend Pearl Harbor. VS-6 lost six planes during the attack. VB-6 lost one. Many of these planes were shot down by the Japanese. However, at least one plane was lost to anti-aircraft (AA) fire, and many more were damaged. During the battle, one radio report was heard: "Do not attack me, this is Six Baker Three an American plane". Later, the same pilot (Ensign Manuel Gonzales from VB-6) was heard telling his radioman/gunner to get ready to land on the water. Lieutenant C. E. Dickinson and his crewmate William C. Miller, from VS-6, shot down one Japanese plane before they had to jump out after their plane caught fire. Dickinson later went to Ford Island to fly another plane. He took part when the United States were searching for the Japanese fleet.
"Enterprise" also sent up six F4F Wildcats from Fighting Squadron Six (VF-6) during the attack. All of these aircraft except two were shot down by shellshocked AA gunners when they tried to land on Ford Island later that night. "Enterprise" got her aircraft ready to go on a large search for the Japanese force that attacked Pearl Harbor. They search was to the south and west of Oahu. However, the Japanese had started moving northwest. "Enterprise" went into Pearl Harbor for fuel and supplies on the night of 8 December. Early the next morning, she went to patrol the rest of the Hawaiian Islands to make sure there were no more attacks. Even though the group did not find any ships, "Enterprise" aircraft sank Japanese submarine . "I-70" was sunk at on 10 December 1941.
During the last two weeks of December 1941, "Enterprise" and her group moved to the west of Hawaii to make sure those islands were not attacked. Two other groups tried to help at Wake Island at the same time. After the "Enterprise" group had a short rest at Pearl Harbor, they left on 11 January. They were protecting ships sending help to Samoa. On 1 February, "Enterprise"'s Task Force 8 raided Kwajalein, Wotje, and Maloelap in the Marshall Islands. They sank three ships, damaged eight and destroyed many aircraft.
Five days later, "Enterprise" sailed for the South Pacific to help other U.S. carriers in the Coral Sea. However, the Battle of the Coral Sea was over before "Enterprise" got there.
On 28 May, "Enterprise" moved, as Rear Admiral Raymond A. Spruance's flagship, to Midway. She was ordered to hold Midway and do as much damage to the enemy as possible. USS "Hornet", six cruisers and 10 destroyers were with "Enterprise" on that day.
Both the Americans and Japanese launched air attacks. Even though the fighting went on until 7 June, by the end of 4 June the result had been decided. The Battle of Midway began on the morning of 4 June 1942, when four Japanese carriers attacked on Midway Island. The Japanese did not know that the U.S. Navy was in the area. Just three hours after the first bomb hit Midway, planes from the U.S. carriers attacked. "Enterprise" launched an attack using torpedo bombers, but this failed. Soon after this, "Enterprise" dive bombers attacked and sank the Japanese carriers and . Later in the afternoon, bombers from "Enterprise" and USS "Yorktown" sank (aircraft from "Yorktown" also sank ). "Yorktown" and USS "Hammann" were the only American ships sunk, but 113 planes were lost. 61 of these were lost during the attacks. Japanese losses were much bigger. They lost four carriers, one cruiser and 272 planes. Even though she lost many planes, "Enterprise" returned to Pearl Harbor on 13 June 1942 undamaged.
After a month of rest, "Enterprise" headed on 15 July 1942 for the South Pacific. There, she helped support the attack on the Solomon Islands on 8 August. During the Battle of the Eastern Solomons, the Japanese light carrier "Ryūjō" was sunk. The Japanese troops that were supposed to land on Guadalcanal was forced back. "Enterprise" was hit three times. 77 sailors were killed and 91 were hurt. "Enterprise" was damaged badly.
"Enterprise" was fixed at Pearl Harbor from 10 September-16 October 1942.
On 13 November, pilots from "Enterprise" helped to sink . When the Naval Battle of Guadalcanal ended on 15 November 1942, "Enterprise" had helped to sink 16 ships and damage eight more.
On July 20 1943, "Enterprise" started being upgraded. These happened over several months. She was given an anti-torpedo blister. This meant that the carrier would be protected more against torpedoes.
"Enterprise" was back by November 1943. She helped the U.S. soldiers landing on Makin Atoll from 19–21 November 1943.
"Enterprise" launched planes to strike the Marshall Islands and helped U.S. soldiers land on Kwajalein from 29 January-3 February 1944. Then she went to strike the Japanese base in Truk Lagoon in the Caroline Islands on 17 February.
"Enterprise" launched planes to hit Jaluit Atoll on 20 February. She helped troops who were landing on Emirau Island (19–25 March). On 14 April she helped troops to land in Hollandia (currently known as Jayapura), in New Guinea.