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Pyrylium
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. Synthesis Pyrylium salts are easily produced from simple starting materials through a condensation reaction. Pyrylium salts with aromatic substituents, such 2,4,6-triphenylpyrylium tetrafluoroborate, can be obtained from two moles of acetophenone, one mole of benzaldehyde, and excess tetrafluoroboric acid. For pyrylium salts with alkyl substituents, such as 2,4,6-trimethylpyrylium salts, the best method uses the Balaban- Nenitzescu-Praill synthesis from tertiary butanol and acetic anhydride in the presence of tetrafluoroboric, perchloric, or trifluoromethanesulfonic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selenopyrylium
Selenopyrylium is an aromatic compound, aromatic heterocyclic compound consisting of a six-membered ring with five carbon atoms and a positively charged selenium atom. Naming and numbering Formerly it was named selenapyrylium. However, this is misleading as "selena" indicates that selenium substitutes for a carbon atom, but actually selenium is substituted for the oxygen atom in pyrylium. In the Hantzsch-Widman system of nomenclature, it is called seleninium. This is the name used by Chemical Abstracts. Replacement nomenclature would call this selenoniabenzene. Numbering in selenopyrylium starts with 1 on the selenium atom and counts up to 6 on the carbon atoms. The positions adjacent to the chalcogen, numbered 2 and 6 can also be called α, the next two positions 3 and 5 can be termed "β" and the opposite carbon at position 4 can be called "γ". Occurrence Because selenopyrylium is a positively charged ion, it takes the solid form as a salt with non-nucleophillic anions such as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telluropyrylium
Telluropyrylium is an aromatic heterocyclic compound consisting of a six member ring with five carbon atoms, and a positively charged tellurium atom. Derivatives of telluropyrylium are important in research of infrared dyes. Naming and numbering Formerly it was named tellurapyrylium. However this is misleading, as "tellura" indicates that tellurium substitutes for carbon atom, but actually tellurium is substituted for the oxygen atom in pyrilium. In the Hantzsch-Widman system it is called tellurinium. This is the name used by Chemical Abstracts. Replacement nomenclature would call this telluroniabenzene. Numbering in telluropyrylium starts with 1 on the tellurium atom and counts up to 6 counter-clockwise on the carbon atoms. The positions adjacent to the chalcogen, numbered 2 and 6 can also be called α, the next two positions 3 and 5 can be termed "β" and the opposite carbon at position 4 can be called "γ". Occurrence Because telluropyrylium is a positively charged cation, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thiopyrylium
Thiopyrylium is a cation with the chemical formula C5H5S+. It is analogous to the pyrylium cation with the oxygen atom replaced by a sulfur atom. Thiopyrylium salts are less reactive than the analogous pyrylium salts due to the higher polarizability of the sulfur atom. Among the chalcogenic 6-membered unsaturated heterocycles, thiopyrylium is the most aromatic, due to sulfur having the similar Pauling electronegativity as carbon and only a slightly higher covalent radius. In water, thiopyrylium reacts to it and forms a mixture of 2-hydroxythiopyran and 4-hydroxythiopyran. Thiopyrylium salts can be synthesized by hydrogen abstraction from thiopyran by a hydride ion acceptor, such as trityl perchlorate. The thiopyrylium analogue of 2,4,6-trisubstituted pyrylium salts can be synthesized by treatment with sodium sulfide followed by precipitation with acid. This reaction causes the oxygen atom in the pyrylium cation to be substituted with sulfur. See also * Pyrylium * Selenopyryl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzene
Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly Combustibility and flammability, flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline. It is used primarily as a Precursor (chemistry), precursor to the manufacture of chemicals with more complex structures, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although benzene is a major Chemical industry, industrial che ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated Polymer, polymeric chains, which show significant electrical conductivity. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide. Properties Physical properties Pyridine is diamagnetism, diamagnetic. Its critical point (thermodynamics), critical parameters are: pressure 5.63 MPa, temperature 619 K and volume 248 cm3/mol. In the temperatur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterocyclic Compound
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles. Examples of heterocyclic compounds include all of the nucleic acids, the majority of drugs, most biomass (cellulose and related materials), and many natural and synthetic dyes. More than half of known compounds are heterocycles. 59% of US FDA-approved drugs contain nitrogen heterocycles. Classification The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and the preponderance of work and applications involves unstrained organic 5- and 6-membered rings. Included are pyridine, thiophene, pyrrole, and furan. Another large class of organic heterocycles refers to those fused to benzene rings. For example, the fused benzene derivatives of py ... [...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 Buchares ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aromaticity
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The earliest use of the term was in an article by August Wilhelm Hofmann in 1855. There is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds. Aromaticity can also be considered a manifestation of cyclic delocalization and of resonance. This is usually considered to be because electrons are free to cycle around circular arrangements of atoms that are alternately single- and double- bonded to one another. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by Kekulé (see History section below). Each bond may be seen as a hybrid of a single bo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Costin Nenițescu
Costin D. Nenițescu (in some places ''Nenitzescu'' (; 15 July 1902 – 28 July 1970)) was a prominent Romanian chemist, and a professor at the Politehnica University of Bucharest. He was a titular list of members of the Romanian Academy, member of the Romanian Academy, a corresponding member of the German Academy of Sciences at Berlin, German Academy of Sciences in Berlin, and a member of the German National Academy of Sciences Leopoldina, Leopoldina Academy of Natural Scientists in Halle, Saxony-Anhalt, Halle-Saale. Early life He was born in Bucharest, the son of (lawyer and politician, director of the National Bank of Romania and Minister of Industry and Commerce) and Elena Nenițescu, and the nephew of the writer Ioan S. Nenițescu. After completing in 1920 his secondary studies at Gheorghe Lazăr National College (Bucharest), Gheorghe Lazăr High School, Nenițescu continued his studies at the ETH Zurich, Polytechnic Institute in Zurich and Ludwig Maximilian University of M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acetonitrile
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not classed as organic). It is produced mainly as a byproduct of acrylonitrile manufacture. It is used as a polar aprotic solvent in organic synthesis and in the purification of butadiene. The skeleton is linear with a short distance of 1.16 Å. Acetonitrile was first prepared in 1847 by the French chemist Jean-Baptiste Dumas. Applications Acetonitrile is used mainly as a solvent in the purification of butadiene in refineries. Specifically, acetonitrile is fed into the top of a distillation column filled with hydrocarbons including butadiene, and as the acetonitrile falls down through the column, it absorbs the butadiene which is then sent from the bottom of the tower to a second separating tower. Heat is then employed in the separa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, alkylation Friedel–Crafts reaction and acylation Friedel–Crafts reaction. Illustrative reactions The most widely practised example of this reaction is the ethylation of benzene. :: Approximately 24,700,000 tons were produced in 1999. (After dehydrogenation and polymerization, the commodity plastic polystyrene is produced.) In this process, acids are used as catalyst to generate the incipient carbocation. Many other electrophilic reactions of benzene are conducted, although on a much smaller scale; they are valuable routes to key intermediates. The nitration of benzene is achieved via the action of the nitronium ion as the electrophile. The Aromatic sulfonation, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, , the conjugate base of perchloric acid (ionic perchlorate). As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cation (). The term ''perchlorate'' can also describe perchlorate esters or covalent perchlorates. These are organic compounds that are alkyl or aryl esters of perchloric acid. They are characterized by a covalent bond between an oxygen atom of the ClO4 moiety and an organyl group. In most ionic perchlorates, the cation is non-coordinating. The majority of ionic perchlorates are commercially produced salts commonly used as oxidizers for pyrotechnic devices and for their ability to control static electricity in food packaging. Additionally, they have been used in rocket propellants, fertilizers, and as bleaching agents in the paper and textile industries. Perchlorate contamination of food and water endangers human health, primarily af ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
