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Costin Nenițescu
Costin D. Neniţescu in some scientific publication written as ''Nenitzescu'' (; 15 July 1902 – 28 July 1970) was a prominent Romanian chemist, and a professor at the Polytechnic University of Bucharest. He was a member of the Romanian Academy, a corresponding member of the German Academy of Sciences in Berlin, and a member of the Leopoldina Academy of Natural Scientists in Halle-Saale. Education and career After completing in 1920 his secondary studies at Gheorghe Lazăr High School, Neniţescu continued his studies at the Polytechnic Institute in Zürich and Ludwig Maximilian University in Munich, where he was one of the favorite students of Hans Fischer. He studied Friedel–Crafts-like reactions in the series of aliphatic hydrocarbons, the mechanism of the isomerization of cyclobasics, the halogen migration in cycles and chains, reactions induced by carbonium ions, and others. He identified a group of naphthenic acids in Romanian crude oil. He searched for ways of obt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stamps Of Romania, 2002-15
Stamp or Stamps or Stamping may refer to: Official documents and related impressions * Postage stamp, used to indicate prepayment of fees for public mail * Ration stamp, indicating the right to rationed goods * Revenue stamp, used on documents to indicate payment of tax * Rubber stamp, device used to apply inked markings to objects ** Passport stamp, a rubber stamp inked impression received in one's passport upon entering or exiting a country ** National Park Passport Stamps * Food stamps, tickets used in the United States that indicate the right to benefits in the Supplemental Nutrition Assistance Program Collectibles * Trading stamp, a small paper stamp given to customers by merchants in loyalty programs that predate the modern loyalty card * Eki stamp, a free collectible rubber ink stamp found at many train stations in Japan Places * Stamp Creek, a stream in Georgia * Stamps, Arkansas People * Stamp or Apiwat Ueathavornsuk (born 1982), Thai singer-songwriter * Stamp (sur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Naphthenic Acid
Naphthenic acids (NAs) are a mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. McKee et al. claim that "naphthenic acids (NAs) are primarily cycloaliphatic carboxylic acids with 10 to 16 carbons" .html" ;"title="/sup>">/sup>, although acids containing up to 50 carbons have been identified in heavy petroleum.Qian, K. and W.K. Robbins (2001). Resolution and identification of elemental compositions for more than 3000 crude acids in heavy petroleum by negative-ion microelectrospray high-field Fourier Transform ion cyclotron resonance mass spectrometry. ''Energy & Fuels.'' 15:1505-1511. The term naphthenic acid has roots in the somewhat archaic term "naphthene" (cycloaliphatic but non-aromatic) used to classify hydrocarbons. It was originally used to describe the complex mixture of petroleum-based acids when the analytical method ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nenitzescu Indole Synthesis
The Nenitzescu indole synthesis is a chemical reaction that forms 5-hydroxyindole derivatives from benzoquinone and β-aminocrotonic esters. This reaction was named for its discoverer, Costin Nenițescu, who first reported it in 1929. It can be performed with a number of different combinations of R-groups, which include methyl, methoxy, ethyl, propyl, and H substituents. There is also a solid-state variation in which the reaction takes place on a highly cross-linked polymer scaffold. The synthesis is particularly interesting because indoles are the foundation for a number of biochemically important molecules, including neurotransmitters and a new class of antitumor compounds. Mechanism The mechanism of a Nenitzescu reaction consists of a Michael addition, followed by a nucleophilic attack by the enamine pi bond, and then an elimination. The reaction was first published by Nenitzescu in 1929, and has since been refined by Allen ''et al.'' In his 1996 publication, Allen and co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene is widely used in the chemical industry, and its worldwide production (over 150 million tonnes in 2016) exceeds that of any other organic compound. Much of this production goes toward polyethylene, a widely used plastic containing polymer chains of ethylene units in various chain lengths. Ethylene is also an important natural plant hormone and is used in agriculture to force the ripening of fruits. The hydrate of ethylene is ethanol. Structure and properties This hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar. The H-C-H angle is 117.4°, close to the 120° for ideal sp² hybridized carbon. The molecule is also relatively weak: rota ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymerisation
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. In chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and their inherent steric effects. In more straightforward polymerizations, alkenes form polymers through relatively simple radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize. Alkanes can also be polymerized, but only with the help of strong acids. As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as polyethylene and polyvinyl chloride (PVC), whi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Serotonin
Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction. Approximately 90% of the serotonin that the body produces is in the intestinal tract. Biochemically, the indoleamine molecule derives from the amino acid tryptophan, via the (rate-limiting) hydroxylation of the 5 position on the ring (forming the intermediate 5-hydroxytryptophan), and then decarboxylation to produce serotonin. Serotonin is primarily found in the enteric nervous system located in the gastrointestinal tract (GI tract). However, it is also produced in the central nervous system (CNS), specifically in the raphe nuclei located in the brainstem, Merkel cells located in the skin, pulmonary neuroendocrine cells and taste receptor cells in the tongue. Additionally, serotonin is stored in blood platelets and is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tryptamine
Tryptamine is an indolamine metabolite of the essential amino acid, tryptophan. The chemical structure is defined by an indole ─ a fused benzene and pyrrole ring, and a 2-aminoethyl group at the second carbon (third aromatic atom, with the first one being the heterocyclic nitrogen). The structure of tryptamine is a shared feature of certain aminergic neuromodulators including melatonin, serotonin, bufotenin and psychedelic derivatives such as dimethyltryptamine (DMT), psilocybin, psilocin and others. Tryptamine has been shown to activate trace amine-associated receptors expressed in the mammalian brain, and regulates the activity of dopaminergic, serotonergic and glutamatergic systems. In the human gut, symbiotic bacteria convert dietary tryptophan to tryptamine, which activates 5-HT4 receptors and regulates gastrointestinal motility. Multiple tryptamine-derived drugs have been developed to treat migraines, while trace amine-associated receptors are being explored as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" may also refer to the specific compound , also called methylene, the parent hydride from which all other carbene compounds are formally derived. Carbenes are classified as either singlets or triplets, depending upon their electronic structure. Most carbenes are very short lived, although persistent carbenes are known. One well-studied carbene is dichlorocarbene , which can be generated ''in situ'' from chloroform and a strong base. Structures and bonding The two classes of carbenes are singlet and triplet carbenes. Singlet carbenes are spin-paired. In the language of valence bond theory, the molecule adopts an sp2 hybrid structure. Triplet carbenes have two unpaired electrons. Most carbenes have a nonlinear triplet ground state, e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexandru Balaban
Alexandru T. Balaban (born April 2, 1931 in Timișoara) is a Romanian chemist who made significant contributions to the fields of organic chemistry, theoretical chemistry, mathematical chemistry, and chemical graph theory. Early life and education Balaban was born in Timișoara, in the western part of Romania. His parents (Teodor and Florica Balaban) paid a lot of attention to Balaban's education, strongly encouraging his fascination with chemistry. In 1935 his family moved to Bucharest, where Balaban attended elementary school. After World War II, in 1945 they moved to Petroșani, where he finished high school. Alexandru Balaban enrolled the Politehnica University of Bucharest in 1949, where he was awarded a Ph.D. in chemistry on April 2, 1959. The topic of his Ph.D. thesis dealt with the restrictions catalyzed by anhydrous aluminium chloride. Career For more than forty years, Balaban held positions at the Chair of Organic Chemistry of the Politehnica University of Buchare ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrylium Salt
Pyrylium is a cation (positive ion) with formula , consisting of a six-membered ring of five carbon atoms, each with one hydrogen atom, and one positively charged oxygen atom. The bonds in the ring are conjugated as in benzene, giving it an aromatic character. In particular, because of the positive charge, the oxygen atom is trivalent. Pyrilium is a mono-cyclic and heterocyclic compound, one of the oxonium ions. Salts Pyrylium and its derivatives form stable salts with a variety of anions. Derivatives Many important cations are formally derived from pyrylium by substitution of various functional groups for some or all the hydrogens in the ring. The 2,4,6-triphenylpyrilium, referred to as the Katritzky salt, (after Alan R. Katritzky) is an important example used in many modern examples of metal catalyzed cross-couplings. Chemical properties Like other oxonium ions, pyrylium is unstable in neutral water. However, pyrylium is much less reactive than ordinary oxonium ions beca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromic Oxychloride
Chromyl chloride is the inorganic compound with the formula CrO2Cl2. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal complexes. Preparation Chromyl chloride can be prepared by the reaction of potassium chromate or potassium dichromate with hydrogen chloride in the presence of sulfuric acid, followed by distillation. :K2Cr2O7 + 6 HCl → 2 CrO2Cl2 + 2 KCl + 3 H2O The sulfuric acid serves as the dehydration agent. It can also be prepared directly by exposing chromium trioxide to anhydrous hydrogen chloride gas. :CrO3 + 2 HCl ⇌ CrO2Cl2 + H2O The method used to prepare chromyl chloride is the basis for a qualitative test for chloride: a sample suspected of containing chloride is heated with a mixture of potassium dichromate and concentrated sulfuric acid. If chloride is present, chromyl chloride forms as evidenced by red fumes of CrO2Cl2. Analogous compounds are not formed with fluorides, bromides, iodides and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromic Acid
The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the molecular species, H2CrO4 of which the trioxide is the anhydride. Chromic acid features chromium in an oxidation state of +6 (or VI). It is a strong and corrosive oxidising agent. Molecular chromic acid Molecular chromic acid, H2CrO4, has much in common with sulfuric acid, H2SO4. Only sulfuric acid can be classified as part of the 7 strong acids list. Due to the laws pertinent to the concept of "first order ionization energy", the first proton is lost most easily. It behaves extremely similar to sulfuric acid deprotonation. Since the process of polyvalent acid-base titrations have more than one proton (especially when the acid is starting substance and the base is the titrant), proton ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
