Archives November 2013

As with alkenes, the addition of water to alkynes requires a strong acid, usually sulfuric acid, and is facilitated by mercuric sulfate. However, unlike the additions to double bonds which give alcohol products, addition of water to alkynes gives ketone products ( except for acetylene which yields acetaldehyde ). The explanation for this deviation lies in enol-keto tautomerization, illustrated by the following equation. The initial product from the addition of water to an alkyne is an enol (a compound having a hydroxyl substituent attached to a double-bond), and this immediately rearranges to the more stable keto tautomer. Tautomers are defined as rapidly interconverted constitutional isomers, usually distinguished by a different bonding location for a labile hydrogen atom (colored red here) and a differently located double bond. The equilibrium between tautomers is not only rapid under normal conditions, but it often strongly favors one of the isomers ( acetone, for example, more...

The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new alkane:   2R–X + 2Na → R–R + 2Na+X−   Other metals have also been used to effect the Wurtz coupling, among them silver, zinc, iron, activated copper, indium and a mixture of manganese and copper chloride. The related reaction dealing with aryl halides is called the Wurtz-Fittig reaction.This can be explained by the formation of free radical intermediate and its subsequent disproportionation to give alkene. The reaction consists of a halogen-metal exchange involving the radical species R• (in a similar fashion to the formation of a Grignard reagent and then the carbon–carbon bond formation in a nucleophilic substitution reaction.) One electron from the metal is transferred to the halogen to produce a metal halide and more...

"We have never succeeded In slowing down our nuclear fusion reactors." Wilson Greatbatch, inventor In 1950 Andrei Sakharov (1921-1989) took a break from designing nuclear weapons to study plasma physics with Igor Tamm (1895-1971) for a year, during which time they developed the concept for a machine that could produce energy through nuclear fusion. Tamm went on to win the 1958 Nobel Prize in Physics; Sakharov was awarded the 1975 Nobel Peace Prize. Progress on fusion power has been slow. Nuclear fission produces energy by splitting highly radioactive atoms of uranium or plutonium. However, fission also produces waste that is dangerously radioactive for 10,000 years. Fusion, on the other hand, produces energy by combining deuterium (heavy hydrogen) into helium, with no dangerous waste. Sea water has one atom of deuterium for each 6,500 atoms of hydrogen. Deuterium atoms are twice as massive as hydrogen atoms, so they are relatively easy more...

An auto rickshaw is a form of transport which does not depend on human muscles yet is cheaper than a taxi, both to run and use. It consists essentially of a motorcycle engine mounted on a three-wheeled chassis, with space for passengers and a driver. Its single steering wheel is at the front, below the Windscreen, with the two driven wheels at the back. The passengers are well protected from the weather by a canvas hood. The driver sits in front with the engine beneath his seat. The passengers' compartment is at the back. (The life of an auto rickshaw driver is very hard. He has to bear hot winds during summer season. He has to face bone biting cold winds in the winter. Even rainy season too does not favour him. Sometimes he gets drenched and sometimes he has to face the muddy water forcing him to draw his more...

“I have little patience with scientists who... drill...holes where drilling is easy." Albert Einstein, theoretical physicist Stone Age man figured out that spinning a sharp rock on a wooden board would produce a circular hole—a useful discovery. The application of a bow to such a drill increased the rate of spinning and therefore the speed of boring the hole. By the nineteenth century, the bow had been replaced by geared machinery and the stone bit by metal, but otherwise the concept remained basically the same. Prior to the early 1860s, the standard drill bit consisted simply of a flattened, sharpened piece of metal. These "spade bits" were notoriously imprecise and also prone to rapid dulling when used on hard surfaces. American Stephen Morse believed that he could improve the standard drill bit, and, in 1861, he patented what has now become known as the twist drill. The device was the more...

"Anything that needs communications or control will be wirelessly connected." Vie Hayes Today's wireless networks owe much to one of the earliest computer networks, the University of Hawaii's ALOHAnet. This radio-based system, created in 1970, had many of the basic principles still in use today. Early wireless networks were expensive, however, and their equipment was bulky. They were used only in places where wired networks were awkward, such as across water or difficult terrain. It was not until the 1980s, with the arrival of cheaper, more portable equipment, that wireless networking began to go mainstream. There was a problem, however. By the end of the 1980s several companies were selling wireless networking equipment, but it was all incompatible. What was needed was some joined-up thinking. Step forward the Institute of Electrical and Electronic Engineers (IEEE) and in particular Vie Hayes {b. 1941). Hayes did not invent any new technology, but more...

"The telephone is a good way to talk to people without having to offer them a drink." Fran Lebowitz, writer Superheroes may use phone booths to change into spandex, prostitutes may use them to place calling cards, and hooligans occasionally abuse them as urinals, but the impetus for the first payphone initially sprang out of an individual's desperate need for the use of a telephone and not being able to find one. Conscious of this need, U.S. inventor William Gray devised the first coin-operated pay phone in 1889. It was a post-pay machine so the money was paid after the call to an attendant. Demand for .the device was not immediate, but he managed to interest telephone companies, hotels, and shops. As people traveled more, the need for public payphones grew, and Gray's idea fueled the demand for household telephones. Phone booths have undergone more design changes over the years more...

“[I was] ...the instrument destined to take away from the world one of its greatest calamities..." Edward Jenner, scientist and doctor As Edward Jenner (1749-1823) was growing up in England, smallpox had again become prevalent and was ravaging London and the countryside. Jenner became a doctor, practicing in Gloucestershire where he became interested in the link between cowpox and smallpox. Milkmaids who contracted the non- deadly cowpox seemed immune to smallpox, and Jenner, intrigued by this, began to investigate the link. In May 1796, milkmaid Sarah Nelmes contracted cowpox from her cow, and pus-filled blisters covered her hands and arms. She visited Dr. Jenner. Realizing his opportunity to test the protective properties of cowpox on someone who had not contracted smallpox, Jenner took some pus from Sarah and applied it to scratches made on the arm of a young boy, James Phipps. Some days later Phipps came down with a more...

Resistance The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it.  If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behavior of the material. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors.Whether or not a material obeys Ohm's law, its resistance can be described in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance.  Resistivity  The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon more...

Chemical Kinetics Chemical kinetics deals with the rates of reactions. In order for a reaction to occur, a collision must occur; the collision must be of sufficient energy to break the necessary bonds and be of proper orientation. This is the basis of reaction rates. Factors effecting reaction rates are concentration of the reacting species found in the rate law, temperature and the presence or absence of a catalyst.  A rate law of a reaction is a mathematical expression relating the rate of a reaction to the concentration of either reactants or products. One may not look at an overall reaction, and determine the rate law. The rate law may be theoretically determined from the rate determining step (slow step) of the reaction mechanism. Many chemical reactions actually require a number of steps in order to break bonds and form new ones. These series of steps are called the reaction mechanism. more...