K. C. Nicolaou
Kyriacos Costa Nicolaou is a Cypriot-American chemist known for his research in the area of natural products total synthesis. He is Harry C. and Olga K. Wiess Professor of Chemistry at Rice University, having held academic positions at The Scripps Research Institute/UC San Diego and the University of Pennsylvania. K. C. Nicolaou was born on July 5, 1946, in Karavas, Cyprus where he grew up and went to school until the age of 18. In 1964, he went to England where he spent two years learning English and preparing to enter University, he studied chemistry at the University of London.. In 1972, he moved to the United States and, after postdoctoral appointments at Columbia University and Harvard University, he joined the faculty at the University of Pennsylvania where he became the Rhodes-Thompson Professor of Chemistry. While at Penn, he won the prestigious Sloan Fellowship. In 1989, he relocated to San Diego, where he took up a joint appointment at the University of California, San Diego, where he served as Professor of Chemistry, The Scripps Research Institute, where he was Darlene Shiley Professor of Chemistry and Chairman of the Department of Chemistry.
In 1996, he was appointed Aline W. and L. S. Skaggs Professor of Chemical Biology in The Skaggs Institute for Chemical Biology, The Scripps Research Institute. From 2005 to 2011, he directed Singapore. In 2013, Nicolaou moved to Rice University; the Nicolaou group is active in the field of organic chemistry with research interests in methodology development and total synthesis. He is responsible for the synthesis of many complex molecules found in nature, such as Taxol and vancomycin, his group's route to Taxol, completed in 1994 at the same time as a synthesis by the group of Robert A. Holton, attracted national news media attention due to Taxol's structural complexity and its potent anti-cancer activity. Endiandric acids A–D Amphoteronolide B and Amphotericin B Calicheamicin γ1 Sirolimus Taxol Zaragozic acid A Brevetoxin B Vancomycin Uncialamycin Viridicatumtoxin B Shishijimicin A Thailanstatin A He is the co-author of three popular books on total synthesis: Classics in Total Synthesis I, 1996 Classics in Total Synthesis II, 2003 Classics in Total Synthesis III, 2011Additionally, he authored or co-authored several other books: Molecules That Changed the World, 2008 Handbook of Combinatorial Chemistry: Drugs, Materials, 2002 Selenium in Natural Products Synthesis, 1984 K. C.
Nicolaou has received numerous awards and honors including: 2016 Wolf Prize in Chemistry 2011 Benjamin Franklin Medal in Chemistry 2005 Arthur C. Cope Award 2003 Nobel Laureate Signature Award in Graduate Education 2002 Tetrahedron Prize 2001 Ernst Schering Prize 2000 Paul Karrer Gold Medal 1998 Esselen Award 1996 Linus Pauling Award Aspirin Prize Max Tishler Prize Lecture Yamada Prize Janssen Prize Nagoya Medal Centenary Medal Inhoffen Medal Nichols Medal ACS Award for Creative Work in Synthetic Organic Chemistry ACS Guenther Award in Natural Products Chemistry Fellow of the American Academy of Arts and Sciences Member of the National Academy of Sciences Foreign Member of the Royal Society Several honorary degrees ^ Nicolaou, Kyriacos Costa. Classics in Total Synthesis: Targets, Methods. Wiley-VCH. ISBN 978-3-527-29231-8. ^ Nicolaou, Kyriacos Costa. Classics in Total Synthesis II: More Targets, Methods. Wiley-VCH. ISBN 978-3-527-30684-8. ^ Nicolaou, Kyriacos Costa. S. Chen. Classics in Total Synthesis III: Further Targets, Methods.
Wiley-VCH. ISBN 978-3-527-32957-1. ^ "Benjamin Franklin Medal in Chemistry". Franklin Institute. 2011. Archived from the original on July 30, 2012. Retrieved December 23, 2011; the Nicolaou group at Rice University A video interview of Professor Nicolaou
N-Butyllithium is an organolithium reagent. It is used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene, it is broadly employed as a strong base in the synthesis of organic compounds as in the pharmaceutical industry. Butyllithium is commercially available as solutions in alkanes such as pentane and heptanes. Solutions in diethyl ether and THF are not stable enough for storage. Annual worldwide production and consumption of butyllithium and other organolithium compounds is estimated at 1800 tonnes. Although butyllithium is colorless, n-butyllithium is encountered as a pale yellow solution in alkanes; such solutions are stable indefinitely if properly stored. Fine white precipitate is deposited and the color changes to orange. N-BuLi exists as a cluster both in a solution; the tendency to aggregate is common for organolithium compounds. The aggregates are held together by delocalized covalent bonds between lithium and the terminal carbon of the butyl chain.
In the case of n-BuLi, the clusters are hexameric. The cluster is a distorted cubane-type cluster with CH2R groups at alternating vertices. An equivalent description describes the tetramer as a Li4 tetrahedron interpenetrated with a tetrahedron 4. Bonding within the cluster is related to that used to describe diborane, but more complex since eight atoms are involved. Reflecting its "electron-deficient character," n-butyllithium is reactive toward Lewis bases. Due to the large difference between the electronegativities of carbon and lithium, the C-Li bond is polarized; the charge separation has been estimated to be 55-95%. For practical purposes, n-BuLi can be considered to react as the butyl anion, n-Bu−, a lithium cation, Li+; the standard preparation for n-BuLi is reaction of 1-bromobutane or 1-chlorobutane with Li metal: 2 Li + C4H9X → C4H9Li + LiX where X = Cl, BrIf the lithium used for this reaction contains 1–3% sodium, the reaction proceeds more than if pure lithium is used. Solvents used for this preparation include benzene and diethyl ether.
When BuBr is the precursor, the product is a homogeneous solution, consisting of a mixed cluster containing both LiBr and BuLi, together with a small amount of octane. BuLi forms a weaker complex with LiCl, so that the reaction of BuCl with Li produces a precipitate of LiCl. Solutions of butyllithium, which are susceptible to degradation by air, are standardized by titration. A popular weak acid is biphenyl-4-methanol, which gives a colored dilithio derivative at the end point. Butyllithium is principally valued as an initiator for the anionic polymerization of dienes, such as butadiene; the reaction is called "carbolithiation": C4H9Li + CH2=CH-CH=CH2 → C4H9-CH2-CH=CH-CH2LiIsoprene can be polymerized stereospecifically in this way. Of commercial importance is the use of butyllithium for the production of styrene-butadiene polymers. Ethylene will insert into BuLi. Butyllithium is a strong base, but it is a powerful nucleophile and reductant, depending on the other reactants. Furthermore, in addition to being a strong nucleophile, n-BuLi binds to aprotic Lewis bases, such as ethers and tertiary amines, which disaggregate the clusters by binding to the lithium centers.
Its use as a strong base is referred to as metalation. Reactions are conducted in tetrahydrofuran and diethyl ether, which are good solvents for the resulting organolithium derivatives. One of the most useful chemical properties of n-BuLi is its ability to deprotonate a wide range of weak Brønsted acids. T-Butyllithium and s-butyllithium are more basic. N-BuLi can deprotonate many types of C-H bonds where the conjugate base is stabilized by electron delocalization or one or more heteroatoms. Examples include acetylenes, methyl sulfides, methylphosphines, furans and ferrocene. In addition to these, it will deprotonate all more acidic compounds such as alcohols, enolizable carbonyl compounds, any overtly acidic compounds, to produce alkoxides, amides and other -ates of lithium, respectively; the stability and volatility of the butane resulting from such deprotonation reactions is convenient, but can be a problem for large-scale reactions because of the volume of a flammable gas produced. LiC4H9 + R-H → C4H10 + R-LiThe kinetic basicity of n-BuLi is affected by the cosolvent.
Ligands that complex Li+ such as tetrahydrofuran, tetramethylethylenediamine, hexamethylphosphoramide, 1,4-diazabicyclooctane further polarize the Li-C bond and accelerate the metalation. Such additives can aid in the isolation of the lithiated product, a famous example of, dilithioferrocene. Fe2 + 2 LiC4H9 + 2 TMEDA → 2 C4H10 + Fe22Schlosser's base is a superbase produced by treating butyllithium with potassium tert-butoxide, it is kinetically more reactive than butyllithium and is used to accomplish difficult metalations. The butoxide anion complexes the lithium and produces butylpotassium, more reactive than the corresponding lithium reagent. An example of the use of n-butyllithium as a base is the addition of an amine to methyl carbonate to form a methyl carbamate, where n-butyllithium serves to deprotonate the amine: n-BuLi + R2NH + 2CO → R2N-CO2Me + LiOMe + BuH Butyl
Water is a transparent, tasteless and nearly colorless chemical substance, the main constituent of Earth's streams and oceans, the fluids of most living organisms. It is vital for all known forms of life though it provides no calories or organic nutrients, its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient pressure, it forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of its solid state; when finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is water vapor. Water moves continually through the water cycle of evaporation, condensation and runoff reaching the sea. Water covers 71% of the Earth's surface in seas and oceans. Small portions of water occur as groundwater, in the glaciers and the ice caps of Antarctica and Greenland, in the air as vapor and precipitation.
Water plays an important role in the world economy. 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers and canals. Large quantities of water and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of chemical substances. Water is central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, sport fishing, diving; the word water comes from Old English wæter, from Proto-Germanic *watar, from Proto-Indo-European *wod-or, suffixed form of root *wed-. Cognate, through the Indo-European root, with Greek ύδωρ, Russian вода́, Irish uisce, Albanian ujë; the identification of water as a substance Water is a polar inorganic compound, at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue.
This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life", it is the only common substance to exist as a solid and gas in normal terrestrial conditions. Water is a liquid at the pressures that are most adequate for life. At a standard pressure of 1 atm, water is a liquid between 0 and 100 °C. Increasing the pressure lowers the melting point, about −5 °C at 600 atm and −22 °C at 2100 atm; this effect is relevant, for example, to ice skating, to the buried lakes of Antarctica, to the movement of glaciers. Increasing the pressure has a more dramatic effect on the boiling point, about 374 °C at 220 atm; this effect is important in, among other things, deep-sea hydrothermal vents and geysers, pressure cooking, steam engine design. At the top of Mount Everest, where the atmospheric pressure is about 0.34 atm, water boils at 68 °C. At low pressures, water cannot exist in the liquid state and passes directly from solid to gas by sublimation—a phenomenon exploited in the freeze drying of food.
At high pressures, the liquid and gas states are no longer distinguishable, a state called supercritical steam. Water differs from most liquids in that it becomes less dense as it freezes; the maximum density of water in its liquid form is 1,000 kg/m3. The density of ice is 917 kg/m3. Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water; the details of the exact chemical nature of liquid water are not well understood. Pure water is described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, frogs are known to be able to smell it. However, water from ordinary sources has many dissolved substances, that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water by avoiding water, too salty or putrid; the apparent color of natural bodies of water is determined more by dissolved and suspended solids, or by reflection of the sky, than by water itself.
Light in the visible electromagnetic spectrum can traverse a couple meters of pure water without significant absorption, so that it looks transparent and colorless. Thus aquatic plants and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them. Water vapour is invisible as a gas. Through a thickness of 10 meters or more, the intrinsic color of water is visibly turquoise, as its absorption spectrum has
Hydrazone iodination is an organic reaction in which a hydrazone is converted into a vinyl iodide by reaction of iodine and a non-nucleophilic base such as DBU. First published by Derek Barton in 1962 the reaction is sometimes referred to as the Barton reaction or, more descriptively, as the Barton vinyl iodine procedure; the reaction has earlier roots with the 1911 discovery by Wieland and Roseeu that the reaction of hydrazones with iodine alone results in the azine dimer. In the original Barton publication the reaction was optimized by using a strong guanidine base, the inverse addition of the hydrazone to an iodine solution, by exclusion of water; when iodine as an electrophile is replaced by aromatic selenyl bromides, the corresponding vinyl selenides are obtained: The reaction mechanism proposed in the original Barton publication is outlined as follows: The hydrazone is oxidized by iodine into a diazo intermediate. In the next step, iodine reacts as an electrophile; when the reaction site is not sterically hindered, a second iodide can recombine to form the geminal di-iodide.
When water is present, the reaction product can revert to the ketone. This reaction is related to the Shapiro reaction. An example of this procedure is the reaction of 2,2,6-trimethylcyclohexanone to the hydrazone by reaction with hydrazine and triethylamine in ethanol at reflux followed by reaction of the hydrazone with iodine in the presence of 2-tert-butyl-1,1,3,3-tetramethylguanidine in diethyl ether at room temperature. Another example can be found in the Danishefsky Taxol total synthesis. In one study it is attempted to trap any reactive intermediate of this reaction with an internal alkene; when the hydrazone 1 in scheme 5 is reacted with iodine and triethylamine in toluene, the expected reaction product is not the di-iodide 10 through path B in a free radical mechanism. The actual process taking place is path A with elimination of HI to the diazo compound 4 followed by a diazoalkane 1,3-dipolar cycloaddition to the pyrazoline 5 in 85% yield. Shapiro reaction
Hydrazones are a class of organic compounds with the structure R1R2C=NNH2. They are related to ketones and aldehydes by the replacement of the oxygen with the NNH2 functional group, they are formed by the action of hydrazine on ketones or aldehydes. The formation of aromatic hydrazone derivatives is used to measure the concentration of low molecular weight aldehydes and ketones, e.g. in gas streams. For example, dinitrophenylhydrazine coated onto a silica sorbent is the basis of an adsorption cartridge; the hydrazones are eluted and analyzed by HPLC using a UV detector. The compound carbonyl cyanide-p-trifluoromethoxyphenylhydrazone is used to uncouple ATP synthesis and reduction of oxygen in oxidative phosphorylation in molecular biology. Phenylhydrazine reacts with glucose to form an osazone. Hydrazone-based coupling methods are used in medical biotechnology to couple drugs to targeted antibodies, e.g. antibodies against a certain type of cancer cell. The hydrazone-based bond is stable at neutral pH, but is destroyed in the acidic environment of lysosomes of the cell.
The drug is thereby released in the cell. In aqueous solution, aliphatic hydrazones are 102- to 103-fold more sensitive to hydrolysis than analogous oximes. Hydrazones are reactants in hydrazone iodination, the Shapiro reaction and the Bamford-Stevens reaction to vinyl compounds. A hydrazone is an intermediate in the Wolff–Kishner reduction. Hydrazones can be synthesized by the Japp–Klingemann reaction via β-keto-acids or β-keto-esters and aryl diazonium salts; the mechanochemical process was used as a green one to synthesize pharmaceutically attractive phenol hydrazones. Hydrazones are converted to azines when used in the preparation of 3,5-disubstituted 1H-pyrazoles, a reaction well known using hydrazine hydrate. In N,N′-dialkylhydrazones the C=N bond can be hydrolysed and reduced, the N-N bond can be reduced to the free amine; the carbon atom of the C=N bond can react with organometallic nucleophiles. The alpha-hydrogen atom is more acidic by 10 orders of magnitude compared to the ketone and therefore more nucleophilic.
Deprotonation with for instance LDA gives an azaenolate which can be alkylated by alkyl halides, a reaction pioneered by Elias James Corey and Dieter Enders in 1978. In asymmetric synthesis SAMP and RAMP are two chiral hydrazines that act as chiral auxiliary with a chiral hydrazone intermediate. Hydrazones Azo compound Imine Nitrosamine Hydrogenation of carbon–nitrogen double bonds
The Bamford–Stevens reaction is a chemical reaction whereby treatment of tosylhydrazones with strong base gives alkenes. It is named for the British chemist William Randall Bamford and the Scottish chemist Thomas Stevens Stevens; the usage of aprotic solvents gives predominantly Z-alkenes, while protic solvent gives a mixture of E- and Z-alkenes. As an alkene-generating transformation, the Bamford–Stevens reaction has broad utility in synthetic methodology and complex molecule synthesis; the treatment of tosylhydrazones with alkyl lithium reagents is called the Shapiro reaction. The first step of the Bamford–Stevens reaction is the formation of the diazo compound 3. In protic solvents, the diazo compound 3 decomposes to the carbenium ion 5. In aprotic solvents, the diazo compound 3 decomposes to the carbene 7; the Bamford–Stevens reaction has not proved useful for the stereoselective generation of alkenes via thermal decomposition of metallated tosylhydrazones due to the indiscriminate 1,2-rearrangement of the carbene center, which gives a mixture of products.
By replacing an alkyl group with a trimethylsilyl group on N-aziridinylimines, migration of a specific hydrogen atom can be enhanced. With the silicon atom beta to H, a σC-Si → σ*C-H stereoelectronic effect weakens the C-H bond, resulting in its exclusive migration and leading to the nearly exclusive formation of allylsilanes instead of equal amounts of allylsilanes and isomeric homoallylsilanes, analogous to the mixture of products seen in the dialkyl case, or other insertion products. See beta-silicon effect. N-tosyldydrazones can be used in a variety of synthetic procedures, their use with arynes has been used to prepare 3-substituted indazoles via two proposed pathways. The first step is the deprotonation of the hydrazone of diazo compounds using CsF. At this point, the conjugate base could either decompose to give the diazo compound and undergo a dipolar cycloaddition with the aryne to give the product, or a annulation with aryne which would give the final product. While strong bases, such as LiOtBu and Cs2CO3 are used in this chemistry, CsF was used to facilitate the in situ generation of arynes from o-aryl triflates.
CsF was thought to be sufficiently basic to deprotonate the N-tosylhydrazone. Barluenga and coworkers developed the first example of using N-tosylhyrdrazones as nucleophilic partners in cross-coupling reactions. Nucleophilic reagents in coupling reactions tend to be of the organometallic variety, namely organomagnesium, -zinc, -tin, -silicon, –boron. Combined with electrophilic aryl halides, N-tosylhydrazones can be used to prepare polysubstituted olefins under Pd-catalyzed conditions without the use of expensive, synthetically demanding organometallic reagents; the scope of the reaction is wide. Moreover, variety of aryl halides are well tolerated as coupling partners including those bearing both electron-withdrawing and electron-donating groups, as well as π-rich and π-deficient aromatic heterocyclic compounds. Stereochemistry is an important element to consider. Using hydrazones derived from linear aldehydes resulted in trans olefins, while the stereochemical outcomes of trisubstituted olefins were dependent on the size of the substituents.
The mechanism of this transformation is thought to proceed in a manner similar to the synthesis of alkenes through the Bamford–Stevens reaction. In this case, the coupling reaction starts with the oxidative addition of the aryl halide to Pd0 catalyst to give the aryl PdII complex; the reaction of the diazocompound, generated from the hydrazone, with the PdII complex produces a Pd-carbene complex. A migratory insertion of the aryl group gives an alkyl Pd complex, which undergoes syn beta-hydride elimination to generate the trans aryl olefin and regenerate the Pd0 catalyst; this reaction has seen utility in preparing conjugated enynes from N-tosylhydrazones and terminal alkynes under similar Pd-catalyzed reaction conditions and following the same mechanism. Moreover and coworkers demonstrated a one-pot three-component coupling reaction of aldehydes or ketones and aryl halides in which the N-tosylhydrazone is formed in situ; this process produces stereoselective olefins in similar yields compared to the process in which preformed N-tosylhydrazones are used.
Barluenga and coworkers developed metal-free reductive coupling methodology of N-tosylhydrazones with boronic acids. The reaction tolerates a variety of functional groups on both substrates, including aromatic, aliphatic, electron-donating and electron-withdrawing substituents, proceeds with high yields in the presence of potassium carbonate; the reaction is thought to proceed through the formation of a diazo compound, generated from a hydrazone salt. The diazo compound could react with the boronic acid to produce the benzylboronic acid through a boronate intermediate. An alternate pathway consists of the formation of the benzylboronic acid via a zwitterionic intermediate, followed by protodeboronation of the benzylboronic acid under basic conditions, which results in the final reductive product; this methodology has been extended to heteroatom nucleophiles to produce ethers and thioethers. A novel process was developed by Stoltz in which the Bamford–Stevens reaction was combined with the Claisen rearrangement to produce a variety of olefin products.
Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is accorded the credit because his work was published first; the name nitrogène was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790, when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the Greek ἀζωτικός "no life", as it is an asphyxiant gas. Nitrogen is the lightest member of group 15 of the periodic table called the pnictogens; the name comes from the Greek πνίγειν "to choke", directly referencing nitrogen's asphyxiating properties. It is a common element in the universe, estimated at about seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2.
Dinitrogen forms about 78 % of Earth's atmosphere. Nitrogen occurs in all organisms in amino acids, in the nucleic acids and in the energy transfer molecule adenosine triphosphate; the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds back into the atmosphere. Many industrially important compounds, such as ammonia, nitric acid, organic nitrates, cyanides, contain nitrogen; the strong triple bond in elemental nitrogen, the second strongest bond in any diatomic molecule after carbon monoxide, dominates nitrogen chemistry. This causes difficulty for both organisms and industry in converting N2 into useful compounds, but at the same time means that burning, exploding, or decomposing nitrogen compounds to form nitrogen gas releases large amounts of useful energy. Synthetically produced ammonia and nitrates are key industrial fertilisers, fertiliser nitrates are key pollutants in the eutrophication of water systems.
Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric and cyanoacrylate used in superglue. Nitrogen is a constituent including antibiotics. Many drugs are mimics or prodrugs of natural nitrogen-containing signal molecules: for example, the organic nitrates nitroglycerin and nitroprusside control blood pressure by metabolizing into nitric oxide. Many notable nitrogen-containing drugs, such as the natural caffeine and morphine or the synthetic amphetamines, act on receptors of animal neurotransmitters. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus, they were well known by the Middle Ages. Alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts; the mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the king of metals. The discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air.
Though he did not recognise it as an different chemical substance, he distinguished it from Joseph Black's "fixed air", or carbon dioxide. The fact that there was a component of air that does not support combustion was clear to Rutherford, although he was not aware that it was an element. Nitrogen was studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as "mephitic air" or azote, from the Greek word άζωτικός, "no life". In an atmosphere of pure nitrogen, animals died and flames were extinguished. Though Lavoisier's name was not accepted in English, since it was pointed out that all gases are mephitic, it is used in many languages and still remains in English in the common names of many nitrogen compounds, such as hydrazine and compounds of the azide ion, it led to the name "pnictogens" for the group headed by nitrogen, from the Greek πνίγειν "to choke".
The English word nitrogen entered the language from the French nitrogène, coined in 1790 by French chemist Jean-Antoine Chaptal, from the French nitre and the French suffix -gène, "producing", from the Greek -γενής. Chaptal's meaning was that nitrogen is the essential part of nitric acid, which in turn was produced from nitre. In earlier times, niter had been confused with Egyptian "natron" – called νίτρον in Greek – which, despite the name, contained no nitrate; the earliest military and agricultural applications of nitrogen compounds used saltpeter, most notably in gunpowder, as fertiliser. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", a monatomic allotrope of nitrogen; the "whirling cloud of brilliant yellow light