Aarushhh/wikipedia-simple-splitted huggingface dataset:
Electricity developed slowly before the war but during the 1920s the electricity industry experienced a huge boom. By 1929 the majority of houses in America had electricity and 70 per cent of them used it for lighting purposes. As a result of the development of factories to produce consumer goods for the American people, the demand for electricity doubled. Electrical power was introduced in factories to drive machinery, and thus it became possible to introduce mass production to a number of factories, e.g. refrigerators, washing machines, vacuum cleaners and radio sets.

The car industry is the best example of mass production during the period. Henry Ford was a pioneer with his idea of producing affordable cars for the people of America. He set about realising his dream by producing his early cars in small workshops. He had groups of men working for him and gradually the cars were built.
Henry Ford and his son posing in the model F Ford car in 1905.
Henry Ford and his son posing in the model F Ford car in 1905
Henry Ford's hard work bore fruit. As he produced more and more cars, he could reduce his prices. By 1925 the price of a car was around $290, which was much cheaper than the price of $850 in 1908. Henry Ford was of the opinion that it was better to sell more cars for a small profit, as that meant employing more workers.

By 1929 Americans owned 23 million cars. The workers earned good wages ($5 per day), thousands of jobs were created, roads were built, petrol stations were built, as were hotels and restaurants. Therefore, the entire economy was given a substantial boost due to the car industry.
In order to help American people to purchase the new goods that were available, systems of hire-purchase and credit were introduced. This meant that a person could buy something by paying for it on a monthly basis. As a result, the majority of Americans could afford expensive goods. In order to encourage Americans to take advantage of the scheme, advertisements were placed on roadsides, on the radio, in newspapers and in cinemas.

During the same period, chain stores appeared for the first time, e.g. J P Penney. Catalogue shopping also became fashionable as it was a convenient way of buying goods.

Economics
Tremors is an American science fiction comedy horror movie. It is set in Nevada and is directed by Ron Underwood. The screenplay was written by S.S. Wilson and Brent Maddock.

Plot
Valentine and Earl want to go to Bixby, Nevada and they leave the Perfection Valley. A subterranean animal kills five people. The Perfection Valley is in danger.

Cast
 Kevin Bacon: Valentine McKee
 Fred Ward: Earl Bassett
 Michael Gross: Burt Gummer
 Reba McEntire: Heather Gummer

Other websites 

1990 comedy movies
1990 horror movies
1990 science fiction movies
1990s science fiction horror movies
American comedy movies
American science fiction horror movies
Comedy horror movies
1990s English-language movies
1990s monster movies
Movies set in Nevada
Universal Pictures movies
Movies directed by Ron Underwood
In biology, a tremor is when antagonist muscles move repeatedly without being controlled. There are different forms of tremors. Very often, a tremor is a symptom for another condition, and not its cause. People with a tremor are not necessarily sick. For example, physiological tremors are measurable, but not visible; they occur in all humans.

Medical signs
Muscular system
The Grignard reaction (pronounced ) is an organometallic chemical reaction in which alkyl- or aryl-magnesium halides (Grignard reagents) attack electrophilic carbon atoms that are present within polar bonds (for example, in a carbonyl group as in the example shown below). Grignard reagents act as nucleophiles. The Grignard reaction produces a carbon–carbon bond. It alters hybridization about the reaction center.  The Grignard reaction is an important tool in the formation of carbon–carbon bonds. It also can form carbon–phosphorus, carbon–tin, carbon–silicon, carbon–boron and other carbon–heteroatom bonds.

It is a nucleophilic organometallic addition reaction. The high pKa value of the alkyl component (pKa = ~45) makes the reaction irreversible. Grignard reactions are not ionic. The Grignard reagent exists as an organometallic cluster (in ether).
The disadvantage of Grignard reagents is that they readily react with protic solvents (such as water), or with functional groups with acidic protons, such as alcohols and amines. Atmospheric humidity can alter the yield of making a Grignard reagent from magnesium turnings and an alkyl halide. One of many methods used to exclude water from the reaction atmosphere is to flame-dry the reaction vessel to evaporate all moisture, which is then sealed to prevent moisture from returning. Chemists then use ultrasound to activate the surface of the magnesium so that it consumes any water present.  This can allow Grignard reagents to form with less sensitivity to water being present.

Another disadvantage of Grignard reagents is that they do not readily form carbon–carbon bonds by reacting with alkyl halides by an SN2 mechanism.
François Auguste Victor Grignard discovered Grignard reactions and reagents. They are named after this French chemist  (University of Nancy, France) who was awarded the 1912 Nobel Prize in Chemistry for this work.

Reaction mechanism
The addition of the Grignard reagent to a carbonyl typically proceeds through a six-membered ring transition state.

However, with steric hindered Grignard reagents, the reaction may proceed by single-electron transfer.
Grignard reactions will not work if water is present; water causes the reagent to rapidly decompose.  So, most Grignard reactions occur in solvents such as anhydrous diethyl ether or tetrahydrofuran (THF), because the oxygen in these solvents stabilizes the magnesium reagent.  The reagent may also react with oxygen present in the atmosphere. This will insert an oxygen atom between the carbon base and the magnesium halide group. Usually, this side-reaction may be limited by the volatile solvent vapors displacing air above the reaction mixture. However, chemists may perform the reactions in nitrogen or argon atmospheres. In small scale reactions, the solvent vapours do not have enough space to protect the magnesium from oxygen.
Making a Grignard reagent
Grignard reagents are formed by the action of an alkyl or aryl halide on magnesium metal.  The reaction is conducted by adding the organic halide to a suspension of magnesium in an ether, which provides ligands required to stabilize the organomagnesium compound.  Typical solvents are diethyl ether and tetrahydrofuran. Oxygen and protic solvents such as water or alcohols are not compatible with Grignard reagents. The reaction proceeds through single electron transfer.

R−X + Mg → R−X•− + Mg•+
R−X•− → R• + X−
X− + Mg•+ → XMg•
R• + XMg• → RMgX

Grignard reactions often start slowly.  First, there is an induction period during which reactive magnesium becomes exposed to the organic reagents.  After this induction period, the reactions can be highly exothermic.  Alkyl and aryl bromides and iodides are common substrates.  Chlorides are also used, but fluorides are generally unreactive, except with specially activated magnesium, such as Rieke magnesium.
Many Grignard reagents, such as methylmagnesium chloride, phenylmagnesium bromide, and allylmagnesium bromide are available commercially in tetrahydrofuran or diethyl ether solutions.

Using the Schlenk equilibrium, Grignard reagents form varying amounts of diorganomagnesium compounds (R = organic group, X = halide):
2 RMgX    R2Mg  +  MgX2

Initiation
Many methods have been developed to initiate Grignard reactions that are slow to start. These methods weaken the layer of MgO that covers the magnesium. They expose the magnesium to the organic halide to start the reaction that makes the Grignard reagent.
Mechanical methods include crushing of the Mg pieces in situ, rapid stirring, or using ultrasound (sonication) of the suspension.  Iodine, methyl iodide, and 1,2-dibromoethane are commonly employed activating agents.  Chemists use 1,2-dibromoethane because its action can be monitored by the observation of bubbles of ethylene.  Also, the side-products are innocuous:
 Mg  +  BrC2H4Br →  C2H4  +  MgBr2
The amount of Mg consumed by these activating agents is usually insignificant.

The addition of a small amount of mercuric chloride will amalgamate the surface of the metal, allowing it to react.

Industrial production
Grignard reagents are produced in industry for use in place, or for sale. As with at bench-scale, the main problem is that of initiation. A portion of a previous batch of Grignard reagent is often used as the initiator. Grignard reactions are exothermic; this exothermicity must be considered when a reaction is scaled-up from laboratory to production plant.

Reactions of Grignard reagents
Reactions with carbonyl compounds
Grignard reagents will react with a variety of carbonyl derivatives.

The most common application is for alkylation of aldehydes and ketones, as in this example:

Note that the acetal function (a masked carbonyl) does not react.

Such reactions usually involve a water-based (aqueous) acidic workup, though this is rarely shown in reaction schemes.  In cases where the Grignard reagent is adding to a prochiral aldehyde or ketone, the Felkin-Anh model or Cram's Rule can usually predict which stereoisomer will form.

Reactions with other electrophiles
In addition, Grignard reagents will react with electrophiles.
Another example is making salicylaldehyde (not shown above). First, bromoethane reacts with Mg in ether. Second, phenol in THF converts the phenol into Ar-OMgBr. Third, benzene is added in the presence of paraformaldehyde powder and triethylamine. Fourth, the mixture is distilled to remove the solvents. Next, 10% HCl is added. Salicylaldehyde will be the major product as long as everything is very dry and under inert conditions. The reaction works also with iodoethane instead of bromoethane.

Formation of bonds to B, Si, P, Sn
The Grignard reagent is very useful for forming carbon–heteroatom bonds.
Carbon–carbon coupling reactions
A Grignard reagent can also be involved in coupling reactions. For example, nonylmagnesium bromide reacts with methyl p-chlorobenzoate to give p-nonylbenzoic acid, in the presence of Tris(acetylacetonato)iron(III), often symbolized as Fe(acac)3, after workup with NaOH to hydrolyze the ester, shown as follows. Without the Fe(acac)3, the Grignard reagent would attack the ester group over the aryl halide.

For the coupling of aryl halides with aryl Grignards, nickel chloride in tetrahydrofuran (THF) is also a good catalyst. Additionally, an effective catalyst for the couplings of alkyl halides is dilithium tetrachlorocuprate (Li2CuCl4), prepared by mixing lithium chloride (LiCl) and copper(II) chloride (CuCl2) in THF. The Kumada-Corriu coupling gives access to [substituted] styrenes.
Oxidation
The oxidation of a Grignard reagent with oxygen takes place through a radical intermediate to a magnesium hydroperoxide. Hydrolysis of this complex yields hydroperoxides and reduction with an additional equivalent of Grignard reagent gives an alcohol.

A reaction of Grignards with oxygen in presence of an alkene makes an ethylene extended alcohol. These are useful in synthesizing larger compounds.  This modification requires aryl or vinyl Grignard reagents. Adding just the Grignard and the alkene does not result in a reaction, showing that the presence of oxygen is essential. The only drawback is the requirement of at least two equivalents of Grignard reagent in the reaction. This can addressed by using a dual Grignard system with a cheap reducing Grignard reagent such as n-butylmagnesium bromide.

Nucleophilic aliphatic substitution
Grignard reagents are nucleophiles in nucleophilic aliphatic substitutions for instance with alkyl halides in a key step in industrial Naproxen production:
Elimination
In the Boord olefin synthesis, the addition of magnesium to certain β-haloethers results in an elimination reaction to the alkene. This reaction can limit the utility of Grignard reactions.

Grignard degradation
Grignard degradation at one time was a tool in structure identification (elucidation) in which a Grignard RMgBr formed from a heteroaryl bromide HetBr reacts with water to Het-H (bromine replaced by a hydrogen atom) and MgBrOH. This hydrolysis method allows the determination of the number of halogen atoms in an organic compound. In modern usage, Grignard degradation is used in the chemical analysis of certain triacylglycerols.

Industrial use
An example of the Grignard reaction is a key step in the industrial production of Tamoxifen. (Tamoxifen is currently used for the treatment of estrogen receptor positive breast cancer in women.):

Gallery
Gallery

Related pages
 Wittig reaction
 Barbier reaction
 Bodroux-Chichibabin aldehyde synthesis
 Fujimoto-Belleau reaction
 Organolithium reagents
 Sakurai reaction

References

Further reading

 
Grignard knowledge: Alkyl coupling chemistry with inexpensive transition metals by Larry J. Westrum, Fine Chemistry  November/December 2002, pp. 10–13  

Organometallic chemistry
Chemical reactions
Peach can mean:

Peach, the fruit or the tree
Princess Peach (or just "Peach"), a video game character
Peach (color)
The Giant Magellan Telescope (GMT) will be the world's largest telescope when it is completed in 2025. Instead of one large mirror, the GMT will have seven separate mirrors working together. This will mean its collecting area is bigger than the actual mirror surfaces. It will be made of seven  diameter mirror parts. It will have a the resolving power of a  mirror. Its collecting area will be the same as a  mirror. The telescope will have over four times the ability to gather light than existing telescopes. It will produce images up to ten times clearer than the Hubble Space Telescope. It will cost $700 million.
Planned site
The location of the telescope is the Las Campanas Observatory, which is also the site of the Magellan Telescopes, some  northeast of La Serena, Chile. This area has clear weather for most of the year. The night sky in most of the surrounding Atacama Desert region is free from atmospheric pollution. With few cities nearby this is probably one of the places least affected by light pollution. All of this makes the area one of the best spots on Earth for long-term astronomical observation.
Design details
The telescope is unique because it will use seven mirror sections, each  in diameter.  These segments will then be arranged to form a single optical surface. This is difficult as the surface of the outer six mirror segments is not radially symmetrical (that is, they are off-axis). This requires a small change in the way mirrors are usually polished. All seven mirrors will be arranged so that the reflecting surface of each of them is on a common axis. One mirror will be in the center and the other six arranged symmetrically around the center. A focal plane will be on-axis with the entire assembly.  The plan is to build seven identical off-axis mirrors. The spare mirror has been made to replace a mirror when it needs recoating, a 1–2 week (per segment) process required every 1–2 years.
The Steward Observatory, at the University of Arizona, is making the mirrors in a laboratory beneath the university's football stadium. It is using a rotating furnace to make the mirror.  The casting of the first mirror was completed on November 3, 2005. But the time-consuming shaping and polishing will be completed in the autumn of 2011.

The telescope will make use of adaptive optics.

Member organizations
The following is a list of the group which is developing the telescope.
Observatories of the Carnegie Institution of Washington (OCIW)
 University of Chicago
 Harvard University
 Smithsonian Astrophysical Observatory
 Texas A&M University
 University of Arizona
 University of Texas at Austin
 Australian National University
 Astronomy Australia Limited
 Korea Astronomy and Space Science Institute
George P. Mitchell, founder of Mitchell Energy & Development Corp., and The Cynthia and George Mitchell Foundation are giving $25 million to help pay for the telescope.

Related pages
Atacama Desert

References
References

Other websites 
 Giant Magellan Telescope home page
 Article from the MIT news office
 New Scientist article on the telescope 
 COSMOS article on the telescope 
 Painted outline of the mirrors at the parking lot of the Observatories of the Carnegie Institution in Pasadena

Telescopes
Atacama Region
Stinging nettles (Urtica dioica) are a type of plant which have stinging defensive hairs on the leaves and stems. Stinging nettles can be found in America, Europe and Asia.

Sting mechanism

The hairs inject histamine and other chemicals that produce a stinging sensation when contacted by humans and other animals. Soaking stinging nettles in water or cooking removes the stinging chemicals from the plant, which allows them to be handled and eaten without injury.

Usage
The plant has been used as medicine, food, tea and fibre. Nettles are sometimes used in cheesemaking, as nettle soup or as substitute for spinach. Its stems contain a bast fibre that is used for the same purposes as linen. Nettles have been used to make clothing for 2,000 years.

Ecology
Stinging nettles are important food plants for several butterflies, like the peacock butterfly and the small tortoiseshell. Also some deers and other animals eat the plant, preferred the leaf shot.

Urticaceae
The Ferrari F50 is a sports car made by Ferrari in 1995. It was created to celebrate the company's 50th anniversary. The car has two doors. It is a two-seated convertible with a removable hardtop. It has a 4.7 L V12 engine that was based on the 3.5 L V12 used in the 1992 Ferrari F92A Formula One car.

Only 349 Ferrari F50's were made. This was because Ferrari wanted it to be rare. The last F50 was produced in Maranello, Italy in July 1997.

It was made in 5 different colors: red, dark red, yellow, black and silver.

The Ferrari F50 can reach a top speed of 205 miles per hour.

Ferrari
A mass spectrum is an intensity versus m/z (mass-to-charge ratio) plot that represents a chemical analysis. The mass spectrum of a sample is a pattern representing the distribution of ions by mass (more correctly: mass-to-charge ratio) in a sample. It is a histogram usually made using an instrument called a mass spectrometer. Not all mass spectra of a given substance are the same. It can depend on the operating conditions of the instrument. For example, some mass spectrometers break the analyte molecules into many pieces; others observe the intact molecular masses with little fragmentation. A mass spectrum can represent many different types of information based on the type of mass spectrometer and the specific experiment; however, all plots of intensity vs. mass-to-charge are called "mass spectra".

Common fragmentation processes for organic molecules are the McLafferty rearrangement and alpha cleavage.
In the past, chemists with PhD degrees were needed to interpret mass spectra. Today, computer programs read the data and identify the compounds in a sample.

References

Other websites
 Interactive tutorial on mass spectra  National High Magnetic Field Laboratory
 Weighing Atoms: A layperson's introduction to mass spectrometry  National High Magnetic Field Laboratory
 What's in an Oil Drop: A layperson's introduction to Fourier Transform Ion Cyclotron Resonance   National High Magnetic Field Laboratory
 Quantities, Units and Symbols in Physical Chemistry (IUPAC green book)
 An introductory video on Mass Spectrometry The Royal Society of Chemistry

Spectroscopy
Mass spectrometry
Stuntman is a racing/action video game that was published by Infogrames and Atari. It was released for the PlayStation 2 and the Game Boy Advance systems. The game is also featured as a mobile phone game which could be downloaded. Stuntman was followed by the 2007 sequel, Stuntman: Ignition. The game received positive reviews, GameSpot gave it a 8.0 out of 10 and IGN gave it a 8.6 out of 10.

The game was followed by sequel, called Stuntman: Ignition released in 2007.

References

Other websites
Stuntman at MobyGames

Racing video games
2002 video games
Game Boy Advance games
PlayStation 2 games
"Eh, Eh (Nothing Else I Can Say)" is a single by Lady Gaga.  It appeared on Gaga's debut album The Fame and was released as a single on January 10, 2009.  Its music video references Gaga's Italian heritage.  Though the single did not chart in the United States, the Recording Industry Association of America certified the song gold on February 29, 2016, for shipments and streams equal to 500,000 copies there.  "Eh, Eh" charted in the top ten in France, New Zealand and Sweden.

2008 songs
Lady Gaga songs
Pop songs
{{DISPLAYTITLE:SN2 reaction}}

The SN2 reaction (also known as bimolecular nucleophilic substitution) is a substitution reaction in organic chemistry. It is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophilic center and bonds to it. This expels another group called a "leaving group". So, the incoming group replaces the leaving group in one step. Since two reacting species are involved in the slow, rate-determining step of the reaction, this leads to the name bimolecular nucleophilic substitution, or SN2. Among inorganic chemists, the SN2 reaction is often known as the interchange mechanism.
Reaction mechanism
The reaction most often occurs at an aliphatic sp3 carbon center with an electronegative, stable leaving group attached to it - 'X' - frequently a halide atom. The breaking of the C-X bond and the formation of the new C-Nu bond occur simultaneously to form a transition state in which the carbon under nucleophilic attack is pentacoordinate, and approximately sp2 hybridized. The nucleophile attacks the carbon at 180° to the leaving group, since this provides the best overlap between the nucleophile's lone pair and the C-X σ* antibonding orbital. The leaving group is then pushed off the opposite side and the product is formed.

If the substrate under nucleophilic attack is chiral, this can lead, although not necessarily, to an inversion of stereochemistry, called the Walden inversion.

In an example of the SN2 reaction, the attack of OH− (the nucleophile) on a bromoethane (the electrophile) results in ethanol, with bromide ejected as the leaving group:
A SN2 reaction occurs if the backside route of attack is not blocked by other atoms in the molecule (sterically hindered by substituents on the substrate). So, this mechanism usually occurs at an unhindered primary carbon center. If there is steric crowding on the substrate near the leaving group, such as at a tertiary carbon center, the substitution will use an SN1 rather than an SN2 mechanism, (an SN1 would also be more likely with blocked molecules because a sufficiently stable carbocation intermediary could be formed.)

In coordination chemistry, associative substitution proceeds by a similar mechanism as SN2.
Factors affecting the rate of the reaction
Four factors affect the rate of the reaction:
 Substrate. The substrate plays the most important part in determining the rate of the reaction. This is because the nucleophile attacks from the back of the substrate, thus breaking the carbon-leaving group bond and forming the carbon-nucleophile bond. Therefore, to maximise the rate of the SN2 reaction, the back of the substrate must be as unhindered as possible. Overall, this means that methyl and primary substrates react the fastest, followed by secondary substrates. Tertiary substrates do not participate in SN2 reactions, because of steric hindrance.
Nucleophile. Like the substrate, steric hindrance affects the nucleophile's strength. The methoxide anion, for example, is both a strong base and nucleophile because it is a methyl nucleophile, and is thus very much unhindered. Tert-butoxide, on the other hand, is a strong base, but a poor nucleophile, because of its three methyl groups hindering its approach to the carbon. Nucleophile strength is also affected by charge and electronegativity: nucleophilicity increases with increasing negative charge and decreasing electronegativity. For example, OH- is a better nucleophile than water, and I- is a better nucleophile than Br- (in polar protic solvents). In a polar aprotic solvent, nucleophilicity increases up a column of the periodic table as there is no hydrogen bonding between the solvent and nucleophile. In this case, nucleophilicity mirrors basicity. I- would therefore be a weaker nucleophile than Br- because it is a weaker base.
Solvent. The solvent affects the rate of reaction because solvents may or may not surround a nucleophile, thus hindering or not hindering its approach to the carbon atom. Polar aprotic solvents, like tetrahydrofuran, are better solvents for this reaction than polar protic solvents because polar protic solvents will be solvated by the solvent hydrogen bonding to the nucleophile. This hinders it from attacking the carbon with the leaving group.

 Leaving group. The leaving group affects the rate of reaction. The more stable leaving group is, the more likely that it will take the two electrons of its carbon-leaving group bond with it when the nucleophile attacks the carbon. Therefore, the weaker the leaving group is as a conjugate base, the better the leaving group. Similarly,  the stronger its corresponding acid, the better the leaving group. Examples of good leaving groups are the halides (except fluoride) and tosylate. But HO- and H2N- are not good leaving groups.
Reaction kinetics
The rate of an SN2 reaction is second order, as the rate-determining step depends on the nucleophile concentration, [Nu−] as well as the concentration of substrate, [RX].

r = k[RX][Nu−]

This is a key difference between the SN1 and SN2 mechanisms. In the SN1 reaction, the nucleophile attacks after the rate-limiting step is over. But in a SN2 reaction, the nucleophile forces off the leaving group in the limiting step. In other words, the rate of SN1 reactions depend only on the concentration of the substrate while the SN2 reaction rate depends on the concentration of both the substrate and nucleophile. In cases where both mechanisms are possible (for example at a secondary carbon center), the mechanism depends on solvent, temperature, concentration of the nucleophile or on the leaving group.

SN2 reactions are generally favored in primary alkyl halides or secondary alkyl halides with an aprotic solvent. They occur at a negligible rate in tertiary alkyl halides due to steric hindrance.
SN2 and SN1 are two extremes of a sliding scale of reactions. It is possible to find many reactions which exhibit both SN2 and SN1 character in their mechanisms. For instance, it is possible to get a contact ion pairs formed from an alkyl halide in which the ions are not fully separated. When these undergo substitution the stereochemistry will be inverted (as in SN2) for many of the reacting molecules but a few may show retention of configuration. SN2 reactions are more common than SN1 reactions.

E2 competition
A common side reaction taking place with SN2 reactions is E2 elimination: the incoming anion can act as a base rather than as a nucleophile, removing a proton and leading to formation of the alkene. This effect can be demonstrated in the gas-phase reaction between a sulfonate and a simple alkyl bromide taking place inside a mass spectrometer:
With ethyl bromide, the reaction product is predominantly the substitution product. As steric hindrance around the electrophilic center increases, as with isobutyl bromide, substitution is disfavored and elimination is the predominant reaction.  Other factors favoring elimination are the strength of the base. With the less basic benzoate substrate, isopropyl bromide reacts with 55% substitution. In general, gas phase reactions and solution phase reactions of this type follow the same trends, even though in the first, solvent effects are dropped.
Roundabout mechanism
A development attracting attention in 2008 concerns a SN2 roundabout mechanism observed in a gas-phase reaction between chloride ions and methyl iodide with a special technique called  crossed molecular beam imaging. When the chloride ions have sufficient velocity, the energy of the resulting iodide ions after the collision is much lower than expected, and it is theorized that energy is lost as a result of a full roundabout of the methyl group around the iodine atom before the actual displacement takes place.

Related pages
 Substitution reaction
 SN1 reaction

References
{{DISPLAYTITLE:SN1 reaction}}
The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step involves only one molecule (unimolecular). The reaction involves a carbocation intermediate. Some common SN1 reactions are of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols.  With primary alkyl halides, the alternative SN2 reaction occurs.  Among inorganic chemists, the SN1 reaction is often known as the dissociative mechanism. Christopher Ingold et al. first proposed the reaction mechanism in 1940.

Mechanism
An example of a reaction taking place with an SN1 reaction mechanism is the hydrolysis of tert-butyl bromide with water to form tert-butyl alcohol:

This SN1 reaction takes place in three steps:
Formation of a tert-butyl carbocation by separation of a leaving group (a bromide anion) from the carbon atom; this step is slow and reversible.

 Nucleophilic attack: the carbocation reacts with the nucleophile. If the nucleophile is a neutral molecule (that is, a solvent) a third step is required to complete the reaction. When the solvent is water, the intermediate is an oxonium ion. This reaction step is fast.

 Deprotonation: Removal of a proton on the protonated nucleophile by water acting as a base forming the alcohol and a hydronium ion. This reaction step is fast.

Because the first step is the bottleneck or "rate-determining step" chemists classify the entire reaction mechanism as SN1. Only one molecule is needed for that step.
Scope of the reaction 
Sometimes a molecule can react using either an SN1 or an SN2 mechanism.
The SN1 mechanism will win this competition when the central carbon atom is surrounded by bulky groups because such groups sterically hinder the SN2 reaction.  Additionally, bulky substituents on the central carbon increase the rate of carbocation formation because of the relief of steric strain that occurs.  The resultant carbocation is also stabilized by both inductive stabilization and hyperconjugation from attached alkyl groups.  The Hammond-Leffler postulate says that this too will increase the rate of carbocation formation.  The SN1 mechanism therefore dominates in reactions at tertiary alkyl centers and is further observed at secondary alkyl centers in the presence of weak nucleophiles.

An example of a reaction proceeding in a SN1 way is the synthesis of 2,5-dichloro-2,5-dimethylhexane from the corresponding diol with concentrated hydrochloric acid:
As the alpha and beta substitutions increase with respect to leaving groups, the reaction is diverted from SN2 to SN1.

Stereochemistry
The carbocation intermediate formed in the reaction's rate limiting step is an sp2 hybridized carbon with trigonal planar molecular geometry.  This allows two different paths for the nucleophilic attack, one on either side of the planar molecule.  If neither path is preferentially favored, these two paths will be used equally, yielding a racemic mix of enantiomers if the reaction takes place at a stereocenter.  This is illustrated below in the SN1 reaction of S-3-chloro-3-methylhexane with an iodide ion, which yields a racemic mixture of 3-iodo-3-methylhexane:
However, an excess of one stereoisomer can be observed, as the leaving group can remain close to the carbocation intermediate for a short time and block nucleophilic attack.  This is very different than the SN2 mechanism, which does not mix the stereochemistry of the product (a stereospecific mechanism).  The SN2 mechanism always inverts the molecule's stereochemistry.
Side reactions
Two common side reactions are elimination reactions and carbocation rearrangement.   If the reaction is performed under warm or hot conditions (which favor an increase in entropy), E1 elimination is likely to predominate, leading to formation of an alkene.  At lower temperatures,  SN1 and E1 reactions are competitive reactions. So, it becomes  difficult to favor one over the other.  Even if the reaction is performed cold, some alkene may be formed.  If an attempt is made to perform an SN1 reaction using a strongly basic nucleophile such as hydroxide or methoxide ion, the alkene will again be formed, this time via an E2 elimination.  This will be especially true if the reaction is heated.  Finally, if the carbocation intermediate can rearrange to a more stable carbocation, it will give a product derived from the more stable carbocation rather than the simple substitution product.
Solvent effects
Solvents will change the reaction rate. Since the SN1 reaction involves formation of an unstable carbocation intermediate in the rate-determining step, anything that can help this will speed up the reaction.  The normal solvents of choice are both polar (to stabilize ionic intermediates in general) and protic (to solvate the leaving group in particular). Typical polar protic solvents include water and alcohols, which will also act as nucleophiles.

The Y scale correlates solvolysis reaction rates of any solvent (k) with that of a standard solvent (80% v/v ethanol/water) (k0) through

with m a reactant constant (m = 1 for tert-butyl chloride),
Y a solvent parameter, and
k0 is the reaction rate using a solvent of 80% ethanol (measured by volume).
For example 100% ethanol gives Y = −2.3, 50% ethanol in water Y = +1.65 and 15% concentration Y = +3.2.

References
References

Further reading
Electrophilic Bimolecular Substitution as an Alternative to Nucleophilic Monomolecular Substitution in Inorganic and Organic Chemistry / N.S.Imyanitov. J. Gen. Chem. USSR (Engl. Transl.) 1990; 60 (3); 417-419.
Unimolecular Nucleophilic Substitution does not Exist! / N.S.Imyanitov. SciTecLibrary

Other websites
 Diagrams: Frostburg State University
 Exercise : the University of Maine
Study Organic Chemistry, Resources for Success in Organic Chemistry
SC Austria Lustenau is a football club from Lustenau, Vorarlberg. The club is playing in the Erste Liga, the second division in Austria.

History
The club was founded in June 1914 as football department of Turnerbund Lustenau and was named FA Turnerbund Lustenau. This name had the club till 1936. For not having a football assosiation in Vorarlberg the club only played friendly matches. During the time of  First World War there were no matches. In 1920 the club started in a regular championship. The first success was the Vorarlberg championship in the 1929/30 season. They were qualified for the Austrian Amateur Championship and reached the final versus Kremser SC.
In 1936 the club left the Turnerbund Lustenau and became a club of its own. The were renamed to SC Austria Lustenau. In the following years they reached several titels.  In 1994 they won the Regionalliga West and were promoted to the First League, the second division in Austrian football. From 1997 to 2000 they played in the Bundesliga, the top division of Austrias football. Since the relegation 2 000 they played in the 2. Liga. In the 2021-22 season they won the league and were promotet to the Bundesliga.

The biggest success so far was the Cup final in 2010/11. Austria Lustenau was the first club from Vorarlberg which ever reached a Cup final. The match was lost against SV Ried. In 2020 they reached again the Cup final but lost again versus FC Red Bull Salzburg.

Current squad 
Updated 17 December 2021.
Honours
Runner-up Austrian Amateur Championship: 1930 (FA Turnerbund)
Champion 2nd division: 1997
Champion Regionalliga West(3rd division): 1994
Champion Tyrol/Vorarlberg: 1977
Vorarlberger Champion: 1930 (FA Turnerbund), 1937, 1946, 1949, 1965, 1977, 1978, 1980 (Austria) , 2005 (Austria-Amateure)
 Vorarlberger Cup : 1936, 1949, 1951, 1958, 1980 (Austria) 1999 (Austria-Amateure)

References

Austrian football clubs
Football clubs of Vorarlberg
Stuntman: Ignition is a racing/action video game that was published by THQ and was developed by Paradigm Entertainment. It was released for the PlayStation 2, PlayStation 3 and the Xbox 360 systems. Stuntman: Ignition was the sequel to the 2002 video game, Stuntman. The game received positive reviews, GameSpot gave it a 7.5 out of 10 and IGN gave it a 7.1 out of 10.

References

Other websites
Stuntman: Ignition at GameSpot

Racing video games
2007 video games
PlayStation 2 games
PlayStation 3 games
Xbox 360 games
THQ games
is a Japanese game designer, professional racing driver, and CEO of Polyphony Digital and producer of the Gran Turismo series.

References

1967 births
Living people
Japanese video game designers
Japanese racecar drivers
People from Chiba Prefecture
The Cradle of Humankind is a World Heritage Site. It was first named by UNESCO in 1999. The site is about 50 kilometres northwest of Johannesburg, South Africa in the Gauteng province, and occupies . 

The site's limestone caves, including the Sterkfontein Caves, were where fossils were found. A 2.3-million year-old fossil Australopithecus africanus (nicknamed 'Mrs. Ples') was found in 1947 by Robert Broom and John T. Robinson. The find followed the 1924 discovery of the juvenile Australopithecus africanus skull, 'Taung Child', by Raymond Dart, at Taung in the North West Province of South Africa, where excavations still continue.

The name Cradle of Humankind reflects the fact that the site has produced a large number, as well as some of the oldest, hominid fossils ever found, some dating back as far as 3.5 million years ago. Sterkfontein alone has produced more than a third of early hominid fossils ever found.
Recent work 
The remains of several partial skeletons of a previously unknown  Australopithecan species were found in 2008 near Johannesburg. They have been dated to about two million year ago (mya). A recent re-examination of two partial skeletons of Australopithecus sediba has led to its identification as close to the origin of the genus Homo. Not all palaeoanthropologists agree this is a new species.
A new analysis shows this species had a human-like pelvis, hands and teeth, and a chimpanzee-like foot. In six separate research reports, palaeontologists reported on the anatomy of a juvenile male skeleton, MH1, a female skeleton, known as MH2, and an isolated adult tibia or shinbone, known as MH4. The findings suggest that some species of australopithecine climbed trees, some walked on the ground, and some did both. 
"Its small heel resembles that of a chimpanzee more than it does a human. This suggests it likely walked with an inward rotation of the knee and hip, with its feet slightly twisted. This primitive way of walking might have been a compromise between upright walking and tree climbing, the researchers suggest, since A. sediba seems to have had more adaptations for tree-climbing than other australopithecines".

Colleagues in England  investigated the teeth. Like other parts of the skeleton, the teeth are a mosaic of primitive and human-like features.

References
References 

Gauteng
Evolution
World Heritage Sites in South Africa
Archaeological sites in Africa
History of South Africa
Prehistoric Africa
Lokomotiv Yaroslavl () is a Russian professional ice hockey team playing in the Kontinental Hockey League (KHL).

2011 plane crash
The Lokomotiv Yaroslavl plane crash occurred on Wednesday, September 7, 2011 at 16:02 local time, when a Yak-Service Yakolev Yak-42 airplane, with the professional ice hockey team and coaching staff of Lokomotiv Yaroslavl of the Kontinental Hockey League, crashed near Yaroslavl, Russia. The team was going to Minsk, Belarus, to start the 2011-12 KHL season against Dinamo Minsk. 44 out of the 45 people on board were confirmed dead, one crew member survived.

Honours 
 Russian Open Championship winner (3): 1996–97, 2001–02, 2002–03
Runners-up of KHL (2): 2007–08, 2008–09
Bronze medal winner of Russian Open Championship and KHL (4): 1997–98, 1998–99, 2004-2005, 2010–11
Runners-up of IIHF Continental Cup : 2003
Bronze medal of Spengler Cup: 2003

Statistics in KHL
Statistics in KHL 

Note: GP = Games played, W = Wins, L = Losses, OTL = Overtime/Shootout Losses, Pts = Points, GF = Goals for, GA = Goals against

References

Other websites
 Lokomotiv Yaroslavl official website
 Home arena, Statistics, History 

Ice hockey teams in Russia
Yaroslavl Oblast
The overhand knot is the simplest knot that can be created.  It is often used as a stopper knot at the end of a rope.

Related pages
 List of knots

Knots
Knot theory is the study of knots in mathematics.  In knot theory, the ends of the rope are attached so that there is no possible way for the knot to be untied.  Peter Guthrie Tait was the first person to make charts describing mathematical knots in the 1860s.

Related pages
 List of knots
 Topology

Further reading 
 Richard H. Crowell and Ralph Fox, Introduction to Knot Theory,  1977, 
 Gerhard Burde and Heiner Zieschang, Knots, De Gruyter Studies in Mathematics, 1985, Walter de Gruyter, 
 Louis H. Kauffman, On Knots, 1987, 

Knots
Topology
A Fabergé egg is one of the jewelled eggs made by Peter Carl Fabergé and his company between 1885 and 1917.

The most famous are those made for the Russian Tsars Alexander III and Nicholas II. They were Easter gifts for their wives and mothers, and are called the 'Imperial' Fabergé eggs. The House of Fabergé made about 52 imperial eggs, of which 46 have survived. Two more were planned for Easter 1918, but were not delivered, due to the Russian Revolution.

List of Fabergé Tsar Imperial Easter eggs 
Below is a list of the eggs made for the Russian imperial family.

List of the Kelch eggs
Faberge also made eggs for Alexander Kelch, a Siberian gold mine industrialist, as gifts for his wife Barbara (Varvara) Kelch-Bazanova.  Most are copies of other eggs.

Other Fabergé eggs

References 

House of Holstein-Gottorp-Romanov
Jewelry
Anthology was a greatest hits album by Selena. The album included remixed songs from Selena's early music career. Two EPs were released as a promotion. The album sold over 1,200,000 copies.

Track listing
Always Mine
No Quiero Saber
Don't Throw Away My Love
La Bamba
I'm Getting Used To You (club remix)
Yo Fui Aquella
Captive Heart
Amame
Missing My Baby
Disco Medley (Full; Club Remix)

Mariachi
Ramalazo
Dame Tu Amor
Pa'Que Me Sirve La Vida
Differentes
Siempre Hace Frio
Que Creias
Quiero Estar Contigo
Rama Caida
Sabes
Tu Solo Tu

Cumbia
Yo Te Dare
La Puerta Se Cerro
Corazoncito
Enamorada de Ti
No Debes Jugar
Carino Mio
Salta La Ranita
Te Amo Solo A Ti
La Llamada
Baila Esta Cumbia

Promotional singles
Two EPs were released. Both of them contained five songs each.

Critical reception
Critical reception

Sales and certifications
Notes
Note that RIAA has launched its Oro y De Platino certification scheme for those albums the 50% of the content of which are in Spanish, initially, the award-levels for Oro y De Platino were: Gold=100,000 and Platinum=200,000. In February 2008, RIAA reduced the certification-award-levels for Oro y De Platino to Gold=50,000 and Platinum=100,000.

References

1998 albums
Selena albums
Greatest hits albums
All My Hits/Todos Mis Exitos was a greatest hits album by Selena. The album included a collectable rose-pin for fans. The album sold over 1,200,000 copies in the United States.

Track lisiting

Critical reception

Sales and certifications 

Notes
Note that RIAA has launched its Oro y De Platino certification scheme for those albums the 50% of the content of which are in Spanish, initially, the award-levels for Oro y De Platino were: Gold=100,000 and Platinum=200,000. In February 2008, RIAA reduced the certification-award-levels for Oro y De Platino to Gold=50,000 and Platinum=100,000.

References

Selena albums
1999 albums
All My Hits/Todos Mis Exitos Vol. 2 was the second series of the All My Hits collection. It was a greatest hits album by Selena. The album included a heart-necklace for fans. The album sold over 400,000 copies in the United States.

Track listing
Enamorada de Ti (Club Remix)
No Quiero Saber
Techno Cumbia (Radio Edit Version)
A Million to One (Medley)
Fotos Y Recuerdos
Si Una Ves
No Me Queda Mas (Astro 95 live)
Siempre Hace Frío
El Chico Del Apartamento 512
Muñequito De Trapo
Captive Heart
Tu Robaste Mi Corazón (with Pete Astudillo)
Bidi Bidi Bom Bom (Astro 95 Live)
Aunque No Salga El Sol (New Version)
Yo Fui Aquella (New Version)
Cien Años (Mirachi Version)
Certifications and sales 
Notes
Note that RIAA has launched its Oro y De Platino certification scheme for those albums the 50% of the content of which are in Spanish, initially, the award-levels for Oro y De Platino were: Gold=100,000 and Platinum=200,000.' In February 2008, RIAA reduced the certification-award-levels for Oro y De Platino to Gold=50,000 and Platinum=100,000.

References

Selena albums
2000 albums
Ones is a greatest hits album by Selena. The album included an unreleased ballad song. The album sold over 500,000 copies in the United States.

Track listing
Disc 1 CD

Disc 2 Music video DVD
No Quiero Saber
La Carcacha
Buenos Amigos (Duet With Álvaro Torres)
La Llamada
Amor Prohibido
No Me Queda Más
Bidi Bidi Bom Bom
Techno Cumbia
Dónde Quiera Que Estés (Duet With Barrio Boyzz)
Tú, Sólo Tú
Siempre Hace Frío
I Could Fall In Love
Dreaming Of You

Certifications

References

Selena albums
2002 albums
JKLF seeks independence of Jammu and Kashmir state from both India and Pakistan.
The JKLF claims that they are not Islamist, but are nationalist, and opposes  the emergence of the territories into either Pakistan or India but rather wants the region of Kashmir to separate from the three countries and become independent.

In 1982 branches were established in Pakistan-administered Kashmir, Pakistan and in 1987 in Indian-administered Kashmir (Jammu and Kashmir).

References 

Kashmir
Nationalist organizations in Asia
National liberation movements
Mirador de la Flor () is a life-sized statue that is in Corpus Christi, Texas. The statue is a memorial to American singer Selena. The statue was ordered by the Mayor of Corpus Christi as a tourist attraction in 1997. Hundreds of fans visit the statue weekly from all over the world. The statue faces Corpus Christi bay, where the gun that killed Selena was thrown. A second life-sized statue of Selena was made in Mexico in March 2011.

References 

Selena
Statues
Buildings and structures in Texas
1997 works
Marie Joséphine of Savoy (Maria Giuseppina Luigia; 2 September 1753 – 13 November 1810) was the wife of the future Louis XVIII of France. She was a princess of Savoy by birth, became the titular Queen consort, and was known by her title: Her Royal Highness, Countess of Provence (comtesse de Provence).

Family

She was born at the Royal Palace of Turin on 2 September 1753 and was the third child and second daughter of Victor Amadeus and his wife the Spanish Infanta Maria Antonia of Spain. At the time of her birth her grandfather, Charles Emmanuel III of Sardinia, was the King of Sardinia.

Marriage
Marriage

Maria Giuseppina was engaged to the French Prince Louis Stanislas of France. He was known as the Count of Provence. They were married on 16 April 1771 by proxy in the Turin. They were married in person on 14 May 1771 at the Palace of Versailles. A luxurious ball followed the wedding on 20 May. She was considered to be ugly. Louis Stanislas hated his wife. We know today that these rumors were created by those who supported Marie Antoinette as a rivalry soon emerged after the youngest brother 'comte d'Artois', married the Comtesse's sister, thereby bringing yet another Savoyard princess to Versailles and creating an Italian party at court.