1.
High-performance liquid chromatography
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High-performance liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pass a pressurized liquid solvent containing the mixture through a column filled with a solid adsorbent material. HPLC has been used for manufacturing, legal, research, Chromatography can be described as a mass transfer process involving adsorption. HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, the active component of the column, the adsorbent, is typically a granular material made of solid particles, 2–50 micrometers in size. The components of the mixture are separated from each other due to their different degrees of interaction with the adsorbent particles. The pressurized liquid is typically a mixture of solvents and is referred to as a mobile phase and its composition and temperature play a major role in the separation process by influencing the interactions taking place between sample components and adsorbent. These interactions are physical in nature, such as hydrophobic, dipole–dipole and ionic, due to the small sample amount separated in analytical HPLC, typical column dimensions are 2. 1–4.6 mm diameter, and 30–250 mm length. Also HPLC columns are made with smaller sorbent particles and this gives HPLC superior resolving power when separating mixtures, which makes it a popular chromatographic technique. The schematic of an HPLC instrument typically includes a sampler, pumps, the sampler brings the sample mixture into the mobile phase stream which carries it into the column. The pumps deliver the flow and composition of the mobile phase through the column. The detector generates a signal proportional to the amount of sample component emerging from the column, a digital microprocessor and user software control the HPLC instrument and provide data analysis. Some models of pumps in a HPLC instrument can mix multiple solvents together in ratios changing in time. Various detectors are in use, such as UV/Vis, photodiode array or based on mass spectrometry. Most HPLC instruments also have an oven that allows for adjusting the temperature at which the separation is performed. The sample mixture to be separated and analyzed is introduced, in a small volume. The components of the move through the column at different velocities. The velocity of each component depends on its nature, on the nature of the stationary phase. The time at which an analyte elutes is called its retention time
2.
Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
3.
Redox
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Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
4.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
5.
Chiral auxiliary
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A chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions, the auxiliary can then be typically recovered for future use. Chiral auxiliaries are one of many strategies available to chemists to selectively produce the desired stereoisomer of a given compound. Chiral auxiliaries were introduced by E. J, Corey in 1975 with chiral 8-phenylmenthol and by B. M. Trost in 1980 with chiral mandelic acid, the menthol compound is difficult to prepare and as an alternative trans-2-phenyl-1-cyclohexanol was introduced by J. K. Whitesell in 1985. Chiral auxiliaries are incorporated into synthetic routes to control the configuration of stereogenic centers. The cost of employing stoichiometric auxiliary and the need to spend synthetic steps appending and removing the auxiliary make this approach appear inefficient, however, for many transformations, the only available stereoselective methodology relies on chiral auxiliaries. In addition, transformations with chiral auxiliaries tend to be versatile and very well-studied, furthermore, the products of auxiliary-directed reactions are diastereomers, which enables their facile separation by methods such as column chromatography or crystallization. In an early example of the use of an auxiliary in asymmetric synthesis. Corey and coworkers conducted an asymmetric Diels-Alder reaction between -8-phenylmenthol acrylate ester and 5-benzyloxymethylcyclopentadiene, the cycloaddition product was carried forward to the iodolactone shown below, an intermediate in the classic Corey synthesis of the prostaglandins. It is proposed that the face of the acrylate is blocked by the auxiliary. -8-phenylmenthol can be prepared from either enantiomer of pulegone, though neither route is very efficient,1, 1’-Binaphthyl-2, 2’-diol, or BINOL, has been used as chiral auxiliary for the asymmetric synthesis since 1983. Hisashi Yamamoto first utilized -BINOL as an auxiliary in the asymmetric synthesis of limonene. -BINOL monoeryl ether was prepared by the monosilylation and alkylation of -BINOL as the chiral auxiliary, followed with the reduction by organoaluminum reagent, limonene was synthesized with low yields and moderate enantiomeric excesses up to 64% ee. The preparation of a variety of enantiomerically pure uncommon R-amino acids can be achieved by the alkylation of chiral glycine derivatives possessing axially chiral BINOL as an auxiliary and it has been depicted by Fuji et al. Based on different electrophile, the diastereomeric excess varied from 69% to 86, Trans-2-phenylcyclohexanol is one type of chiral auxiliary, which was first introduced by James K. Whitesell and his coworkers in 1985. This chiral auxiliary was used in ene reactions of the derived glyoxylate ester, trans-2-cumylcyclohexanol has a similar structure to Trans-2-phenylcyclohexanol. In 2015, Brown group published an efficient method in permanganate-mediated oxidative cyclization with this type of chiral auxiliary, oxazolidinone auxiliaries, popularized by David Evans, have been applied to many stereoselective transformations, including aldol reactions, alkylation reactions, and Diels-Alder reactions
