What is the most common source of polycyclic aromatic hydrocarbons?
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons (PAHs, also polyaromatic hydrocarbons or polynuclear aromatic hydrocarbons) are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings (organic rings in which the electrons are delocalized). The simplest such chemicals are naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene.
Policosanol
Policosanol was originally derived from sugar cane but the chemicals can also be isolated from beeswax, cereal grains, grasses, leaves, fruits, nuts, and seeds of many foods. Plant waxes consist of very long chain fatty acids that have been esterified to very long chain alcohols. Policosanols are very long chain alcohols with carbon backbones ranging from 24 to 34 carbons.
Polyphenol
In these, diverse biosynthetic steps abound: the seven-atom ring (seven-membered ring) appearing in theaflavin structure above is an example of a "carbocycle" that is of a nonbenzenoid aromatic tropolone type. In addition, there are periodic occurrences of:
Because of the preponderance of saccharide-derived core structures (e.g., see tannic acid image above), as well as spiro- and other structure types, natural chiral (stereo) centers abound.
Hexa-cata-hexabenzocoronene
Hexa-cata-hexabenzocoronene (hexabenzo[a,d,g,j,m,p]coronene) is a polycyclic aromatic hydrocarbon with the molecular formula CH. It consists of a central coronene molecule, with an additional benzene ring fused onto each ring around the periphery.
Longifolene
Longifolene is the common (or trivial) chemical name of a naturally occurring, oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound was isolated, "Pinus longifolia" (obsolete name for "Pinus roxburghii" Sarg.)
Polycyclic aromatic hydrocarbon
Some governmental bodies, including the European Union as well as NIOSH and the Environmental Protection Agency (EPA) in the US, regulate concentrations of PAHs in air, water, and soil. The European Commission has restricted concentrations of 8 carcinogenic PAHs in consumer products that contact the skin or mouth.
Oxocarbon
Many hypothetical oxocarbons have been studied by theoretical methods but have yet to be detected. Examples include oxalic anhydride (CO or O=(CO)=O), ethylene dione (CO or O=C=C=O) and other linear or cyclic polymers of carbon monoxide (-CO-) (polyketones), and linear or cyclic polymers of carbon dioxide (-CO-), such as the dimer 1,3-dioxetanedione (CO) and the trimer 1,3,5-trioxanetrione (CO).
Normally, carbon is tetravalent, while oxygen is divalent, and in most oxocarbons (as in most other carbon compounds) each carbon atom may be bound to four other atoms, while oxygen may be bound to at most two. Moreover, while carbon can connect to other carbons to form arbitrarily large chains or networks, chains of three or more oxygens are rarely if ever observed. Thus the known electrically neutral oxocarbons generally consist of one or more carbon skeletons (including cyclic and aromatic structures) connected and terminated by oxide (-O-, =O) or peroxide (-O-O-) groups.
River Clyde
Organic chemical pollution contained in sediments of the Clyde estuary have been evaluated by British Geological Survey. Surface sediments from the Glasgow reaches of the Clyde, Cunningar to Milton, contained polyaromatic hydrocarbons (PAH) from 630 µg/kg to 23,711 µg/kg and polychlorinated biphenyl (PCB) in the range of 5 to 130.5 µg/kg, which classifies these sediments as non-toxic. However, a later study showed PCB concentrations as high as 5,797 µg/kg, which is above published threshold levels for the chlorinated compounds. Comparison of individual PAH compounds with different thermal stabilities shows that the source of PAH pollution in the Clyde changes downriver. PAH in the inner Clyde (Cunningar to Milton) are from combustion sources (vehicle exhaust, coal burning), whereas PAH in the outer Clyde are from petroleum spills
Benzocyclooctatetraene
Benzocyclooctatetraene is a polycyclic hydrocarbon with chemical formula CH, composed of fused a benzene ring and a cyclooctatetraene ring. Only benzene ring is aromatic in this compound.
Anthracene
Anthracene, as many other polycyclic aromatic hydrocarbons, is generated during combustion processes. Exposure to humans happens mainly through tobacco smoke and ingestion of food contaminated with combustion products.
Chrysene
Chrysene is a polycyclic aromatic hydrocarbon (PAH) with the molecular formula that consists of four fused benzene rings. It is a natural constituent of coal tar, from which it was first isolated and characterized. It is also found in creosote at levels of 0.5-6 mg/kg.
NGC 5529
Polycyclic aromatic hydrocarbons (PAHs) have been detected in the mid-infrared spectrum of NGC 5529.
Organic chemistry
Aromatic hydrocarbons contain conjugated double bonds. This means that every carbon atom in the ring is sp2 hybridized, allowing for added stability. The most important example is benzene, the structure of which was formulated by Kekulé who first proposed the delocalization or resonance principle for explaining its structure. For "conventional" cyclic compounds, aromaticity is conferred by the presence of 4n + 2 delocalized pi electrons, where n is an integer. Particular instability (antiaromaticity) is conferred by the presence of 4n conjugated pi electrons.
Hydrocarbon
Aromatic hydrocarbons (arenes), alkanes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons.
Oil pollution toxicity to marine fish
Crude oil contamination in marine ecosystems can lead to both pyrogenic and petrogenic PAHs entering these ecosystems. Petrogenic PAHs can enter waterways through oil seeps, major oil spills, creosote and fuel oil runoff from urban areas. Pyrogenic PAH sources consist of diesel soot tire rubber and coal dust. Although there are natural sources of PAHs such as volcanic activity and seepage of coal deposits, anthropogenic sources pose the most significant input of PAHs into the environment. These anthroprogenic sources include residential heating, asphalt production, coal gasification, and petroleum usage. Petrogenic PAH contamination is more common from crude oil spills such as "Exxon Valdez", or oil seeps; however, with runoff pyrogenic PAHs can also be prevalent. Although major oil spills such as "Exxon Valdez" can introduce a large amount of crude oil to a localized area in a short time span, daily runoff comprises most of the oil pollution to marine ecosystems. Atmospheric deposition can also be a source of PAHs into marine ecosystems. The deposition of PAHs from the atmosphere into a water body is largely influenced by the gas-particle partitioning of the PAH.
Perfluorocarbon tracer
There is a range of PFTs available commercially, allowing the experimenter to release different PFTs at the same time. Cyclic perfluorocarbons, such as perfluoromethylhexane and perfluoro-1,3-dimethylcyclohexane, are generally believed to be better than acyclic ones as they can be detected at lower levels.
Polyhalogenated compound
Polyhalogenated compounds (PHCs) are any compounds with multiple substitutions of halogens. They are of particular interest and importance because they bioaccumulate in humans, and comprise a superset of which has many toxic and carcinogenic industrial chemicals as members. PBDEs, PCBs, dioxins (PCDDs) and PFCs are all polyhalogenated compounds. They are generally non-miscible in organic solvents or water, but miscible in some hydrocarbons from which they often derive.
Polycyclic aromatic hydrocarbon
People can also be occupationally exposed during work that involves fossil fuels or their derivatives, wood burning, carbon electrodes, or exposure to diesel exhaust. Industrial activity that can produce and distribute PAHs includes aluminum, iron, and steel manufacturing; coal gasification, tar distillation, shale oil extraction; production of coke, creosote, carbon black, and calcium carbide; road paving and asphalt manufacturing; rubber tire production; manufacturing or use of metal working fluids; and activity of coal or natural gas power stations.
Risk factors for breast cancer
Aromatic amines are chemicals that are produced when products such as dyes, polyurethane products, and certain pesticides are made. They are also found in cigarette smoke, fuel exhaust, and in over cooked, burned meat. The three types of aromatic amines monocyclic, polycyclic, and heterocyclic have all been found in recent studies of breast health. Monocyclic amines have been found to cause mammary cancer in rats. Studies have shown that women who eat higher amounts of overcooked meat, meaning more exposure to heterocyclic amines, have also been diagnosed with more post-menopausal breast cancer. Heterocyclic amines also have the ability to copy estrogen and in laboratory studies have been found to encourage the growth of cancerous tumors on human tissue.
Pseudoisoeugenol
Pseudoisoeugenol naturally occurs in the essential oils of roots from plants within the genus "Pimpinella". In addition to its standard form, the compound also occurs in a variety of structural derivatives. Common derivatives include the compound with its side chain bearing an epoxide functional group and the aromatic ring being associated with one of many possible esters in the 2nd position. Common esters include angelic acid, 2-methylbutanoic acid, tiglic acid, and 2-methylpropionic acid esters. Hydrolysis of these esters, either "in-vivo" or by using strong acids, forms 2-methyl-5-methoxybenzofuran.
Polyvinyl ether
Polyvinyl ethers are a class of organic polymers derived from vinyl ethers. The most common polymers of this class are derived from methyl vinyl ether and ethyl vinyl ether, the polymer having the formula [CHCH(OCH)]. Commercial interest has also focused on polymers derived from ethyl, isobutyl, octadecyl substituents in place of methyl. Like other vinyl polymers, the polymers exhibit tacticity. Polymerization is typically initiated with Lewis acids such as boron trifluoride.
2-Methylbutanoic acid
2-Methylbutanoic acid (2-methylbutyric acid) is a chemical compound from the group of carboxylic acids. It occurs in two enantiomeric forms, ("R")- and ("S")-2-methylbutanoic acid. ("R")-2-Methylbutanoic acid occurs naturally in cocoa beans and ("S")-2-methylbutanoic occurs in many fruits such as apples and apricots. The ethyl ester is found in pineapples and oranges.
Ethylene glycol poisoning
The most common source of ethylene glycol is automotive antifreeze or radiator coolant, where concentrations are high. Other sources of ethylene glycol include windshield deicing agents, brake fluid, motor oil, developing solutions for hobby photographers, wood stains, solvents, and paints. Some people put antifreeze into their cabin’s toilet to prevent it from freezing during the winter, resulting in toxicities when animals drink from the toilet. Small amounts of ethylene glycol may be contained in holiday ornaments such as snow globes.
Ionic hydrogenation
The most common hydrogenating pair is an organosilane as the hydride source (e.g. triethylsilane), and a strong oxyacid as the proton source (e.g. trifluoroacetic acid or triflic acid). The hydride and proton source cannot combine to give H, which limits the hydricity and acidity of the H and H sources, respectively.
Cyclic compound
Since one of the most commonly encountered aromatic systems of compounds in organic chemistry is based on derivatives of the prototypical aromatic compound benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word “aromatic” is occasionally used to refer informally to benzene derivatives, and this is how it was first defined. Nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the double-ringed bases in RNA and DNA. A functional group or other substituent that is aromatic is called an aryl group.
Grape seed oil
Grapeseed oil has occasionally been found to contain dangerous levels of polycyclic aromatic hydrocarbons because of direct contact with combustion gases during the drying process.
Acid
Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO). On the other hand, for organic acids the term mainly indicates the presence of one carboxylic acid group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid (HCOOH), acetic acid (CHCOOH) and benzoic acid (CHCOOH).
Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic (or dibasic) acid (two potential protons to donate), and triprotic (or tribasic) acid (three potential protons to donate).
Carbonyl sulfide
Carbonyl sulfide is the most abundant sulfur compound naturally present in the atmosphere, at , because it is emitted from oceans, volcanoes and deep sea vents. As such, it is a significant compound in the global sulfur cycle. Measurements on the Antarctica ice cores and from air trapped in snow above glaciers (firn air) have provided a detailed picture of OCS concentrations from 1640 to the present day and allow an understanding of the relative importance of anthropogenic and non-anthropogenic sources of this gas to the atmosphere. Some carbonyl sulfide that is transported into the stratospheric sulfate layer is oxidized to sulfuric acid. Sulfuric acid forms particulate which affects energy balance due to light scattering. The long atmospheric lifetime of COS makes it the major source of stratospheric sulfate, though sulfur dioxide from volcanic activity can be significant too. Carbonyl sulfide is also removed from the atmosphere by terrestrial vegetation by enzymes associated with the uptake of carbon dioxide during photosynthesis, and by hydrolysis in ocean waters. Loss processes, such as these, limit the persistence (or lifetime) of a molecule of COS in the atmosphere to a few years.
Aromatic hydrocarbon
General properties of aromatic hydrocarbons:The circle symbol for aromaticity was introduced by Sir Robert Robinson and his student James Armit in 1925 and popularized starting in 1959 by the Morrison & Boyd textbook on organic chemistry. The proper use of the symbol is debated; it is used to describe any cyclic π system in some publications, or only those π systems that obey Hückel's rule in others. Jensen argues that, in line with Robinson's original proposal, the use of the circle symbol should be limited to monocyclic 6 π-electron systems. In this way the circle symbol for a six-center six-electron bond can be compared to the Y symbol for a three-center two-electron bond.
Aromatic hydrocarbon
A reaction that forms an arene compound from an unsaturated or partially unsaturated cyclic precursor is simply called an aromatization. Many laboratory methods exist for the organic synthesis of arenes from non-arene precursors. Many methods rely on cycloaddition reactions. Alkyne trimerization describes the [2+2+2] cyclization of three alkynes, in the Dötz reaction an alkyne, carbon monoxide and a chromium carbene complex are the reactants. Diels–Alder reactions of alkynes with pyrone or cyclopentadienone with expulsion of carbon dioxide or carbon monoxide also form arene compounds. In Bergman cyclization the reactants are an enyne plus a hydrogen donor.
Polyglycolide
The most common synthesis used to produce a high molecular weight form of the polymer is ring-opening polymerization of "glycolide", the cyclic diester of glycolic acid. Glycolide can be prepared by heating under reduced pressure low MW PGA, collecting the diester by means of distillation. Ring-opening polymerization of glycolide can be catalyzed using different catalysts, including antimony compounds, such as antimony trioxide or antimony trihalides, zinc compounds (zinc lactate) and tin compounds like stannous octoate (tin(II) 2-ethylhexanoate) or tin alkoxides. Stannous octoate is the most commonly used initiator, since it is approved by the FDA as a food stabilizer. Usage of other catalysts has been disclosed as well, among these are aluminium isopropoxide, calcium acetylacetonate, and several lanthanide alkoxides (e.g. yttrium isopropoxide). The procedure followed for ring-opening polymerization is briefly outlined: a catalytic amount of initiator is added to glycolide under a nitrogen atmosphere at a temperature of 195 °C. The reaction is allowed to proceed for about two hours, then temperature is raised to 230 °C for about half an hour. After solidification the resulting high MW polymer is collected.
Biphenyl
It has a distinctively pleasant smell. Biphenyl is an aromatic hydrocarbon with a molecular formula (CH). It is notable as a starting material for the production of polychlorinated biphenyls (PCBs), which were once widely used as dielectric fluids and heat transfer agents.
Limonene
Limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels. The -isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring agent in food manufacturing. It is also used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products. The less common -isomer is found in mint oils and has a piny, turpentine-like odor.
Polyphosphazene
Polyphosphazenes include a wide range of hybrid inorganic-organic polymers with a number of different skeletal architectures that the backbone P-N-P-N-P-N-. In nearly all of these materials two organic side groups are attached to each phosphorus center. Linear polymers have the formula (N=PRR), where R and R are organic (see graphic). Other architectures are cyclolinear and cyclomatrix polymers in which small phosphazene rings are connected together by organic chain units. Other architectures are available, such as block copolymer, star, dendritic, or comb-type structures. More than 700 different polyphosphazenes are known, with different side groups (R) and different molecular architectures. Many of these polymers were first synthesized and studied in the research group of Harry R. Allcock.
The method of synthesis depends on the type of polyphosphazene. The most widely used method for linear polymers is based on a two-step process. In the first step a cyclic small molecule phosphazene, known as hexachlorocyclotriphosphazene, with the formula (NPCl), is heated in a sealed system at 250 °C to convert it to a long chain linear polymer with typically 15,000 or more repeating units. In the second step the chlorine atoms linked to phosphorus in the polymer are replaced by organic groups through reactions with alkoxides, aryloxides, amines or organometallic reagents. Because many different reagents can participate in this macromolecular substitution reaction, and because two or more different reagents may be used, a large number of different polymers can be produced, each with a different combination of properties. Variations to this process are possible using poly(dichlorophosphazene) made by condensation reactions.
Parking lot
Motor vehicles are a constant source of pollutants, the most significant being gasoline, motor oil, polycyclic aromatic hydrocarbons (PAHs), and heavy metals. (PAHs are found in combustion byproducts of gasoline, as well as in asphalt and coal tar-based sealants used to maintain parking lots.) Many parking lots are also significant sources of trash which ends up in waterways.
PAH world hypothesis
The PAH world hypothesis is a speculative hypothesis that proposes that polycyclic aromatic hydrocarbons (PAH), known to be abundant in the universe, including in comets, and, as well, assumed to be abundant in the primordial soup of the early Earth, played a major role in the origin of life by mediating the synthesis of RNA molecules, leading into the RNA world. However, as yet, the hypothesis is untested.
Dibenz(a,j)anthracene
In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs), including dibenz["a","j"]anthracene, in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.
Benzo(c)fluorene
Benzo["c"]fluorene belongs to a group of compounds called polycyclic aromatic hydrocarbons (PAHs). PAHs and their derivatives are ubiquitous in the environment and they are produced in several industrial and combustion processes.
Occupational lung disease
Polycyclic aromatic hydrocarbons (PAHs), fused-ring chemicals formed during the combustion of fossil fuels, are metabolized by the cytochrome P450 complex to highly reactive carbocations, which can mutate DNA and cause cancer. Workers may be exposed to PAHs while working in a foundry, in the roofing industry, or due to environmental tobacco smoke.
Organic mineral
As the name implies, hydrocarbon minerals are composed entirely of carbon and hydrogen. Some are inorganic forms of polycyclic aromatic hydrocarbon (PAH) compounds. For example, a rare mineral known as either carpathite, karpatite or pendletonite is nearly pure coronene. Carpathite is deposited as pale yellow flakes in cracks between diorite (an igneous rock) and argillite (a sedimentary rock); it is prized for a beautiful blue fluorescence under ultraviolet light. Other PAC compounds appearing as minerals include fluorene as kratochvilite; and anthracene as ravatite. Others are mixtures: curtisite contains several PAH compounds, including dibenzofluorine, picene, and chrysene, while the most common components of idrialite are tribenzofluorenes. One theory for their formation involves burial of PAH compounds until they reach a temperature where pyrolisis can occur, followed by hydrothermal transport towards the surface, during which the composition of minerals that precipitate out depends on the temperature.
Organic chemistry
Biomolecular chemistry is a major category within organic chemistry which is frequently studied by biochemists. Many complex multi-functional group molecules are important in living organisms. Some are long-chain biopolymers, and these include peptides, DNA, RNA and the polysaccharides such as starches in animals and celluloses in plants. The other main classes are amino acids (monomer building blocks of peptides and proteins), carbohydrates (which includes the polysaccharides), the nucleic acids (which include DNA and RNA as polymers), and the lipids. In addition, animal biochemistry contains many small molecule intermediates which assist in energy production through the Krebs cycle, and produces isoprene, the most common hydrocarbon in animals. Isoprenes in animals form the important steroid structural (cholesterol) and steroid hormone compounds; and in plants form terpenes, terpenoids, some alkaloids, and a class of hydrocarbons called biopolymer polyisoprenoids present in the latex of various species of plants, which is the basis for making rubber.In pharmacology, an important group of organic compounds is small molecules, also referred to as 'small organic compounds'. In this context, a small molecule is a small organic compound that is biologically active, but is not a polymer. In practice, small molecules have a molar mass less than approximately 1000 g/mol.
Poly(methacrylic acid)
Poly(methacrylic acid) (PMAA) is a polymer made from methacrylic acid. It is often available as its sodium salt, poly(methacrylic acid) sodium salt. preferred IUPAC name 2-Methylprop-2-enoic acid), which is a carboxylic acid. It is a viscous liquid with a pungent odour. The first polymeric form of methacrylic acid was described in 1880 by Engelhorn and Fittig. The use of high purity monomers is required for proper polymerization conditions and therefore it is necessary to remove any inhibitors by extraction (phenolic inhibitors) or via distillation. To prevent inhibition by dissolved oxygen, monomers should be carefully degassed prior to the start of the polymerization.
Methylene cyclopropyl acetic acid
Dihydrosterculic acid is the major carbocyclic fatty acid in the seed oils of "Litchi chinensis". It is a cyclopropene fatty acid; these have been found in many plants of the order Malvales (Sterculiaceae, Malvaceae, Bombaceae and Tiliaceae), in up to 60% of seed oil content, depending on the species but also in leaves, roots and shoots. They are accompanied by small amounts of their cyclopropanoid analogues, i.e. cyclopropyl acetic acid.
Xenobiotic
Some xenobiotics substances are resistant to degradation. Xenobiotics such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and trichloroethylene (TCE) accumulate in the environment due to their recalcitrant properties and have become an environmental concern due to their toxicity and accumulation. This occurs particularly in the subsurface environment and water sources, as well as in biological systems, having the potential to impact human health. Some of the main sources of pollution and the introduction of xenobiotics into the environment come from large industries such as pharmaceuticals, fossil fuels, pulp and paper bleaching and agriculture. For example, they may be synthetic organochlorides such as plastics and pesticides, or naturally occurring organic chemicals such as polyaromatic hydrocarbons (PAHs) and some fractions of crude oil and coal.
Cyclic compound
The earliest use of the term “aromatic” was in an article by August Wilhelm Hofmann in 1855.[1] Hofmann used the term for a class of benzene compounds, many of which do have odors (aromas), unlike pure saturated hydrocarbons. Today, there is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds (how they smell), although in 1855, before the structure of benzene or organic compounds was understood, chemists like Hofmann were beginning to understand that odiferous molecules from plants, such as terpenes, had chemical properties we recognize today are similar to unsaturated petroleum hydrocarbons like benzene.
Arenibacter algicola
Arenibacter algicola is a Gram-negative, hydrocarbon-degrading and strictly aerobic bacterium from the genus of Arenibacter. "Arenibacter algicola" uses polycyclic aromatic hydrocarbons as only sources fore carbon and energy.
Polycyclic aromatic hydrocarbon
PAHs possess very characteristic UV absorbance spectra. These often possess many absorbance bands and are unique for each ring structure. Thus, for a set of isomers, each isomer has a different UV absorbance spectrum than the others. This is particularly useful in the identification of PAHs. Most PAHs are also fluorescent, emitting characteristic wavelengths of light when they are excited (when the molecules absorb light). The extended pi-electron electronic structures of PAHs lead to these spectra, as well as to certain large PAHs also exhibiting semi-conducting and other behaviors.
Amorphous carbon
All practical forms of hydrogenated carbon (e.g. smoke, chimney soot, mined coal such as bitumen and anthracite) contain large amounts of polycyclic aromatic hydrocarbon tars, and are therefore almost certainly carcinogenic.
Alicyclic compound
An alicyclic compound is an organic compound that is both aliphatic and cyclic. They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached.
Simple aromatic ring
Simple aromatic rings can be heterocyclic if they contain non-carbon ring atoms, for example, oxygen, nitrogen, or sulfur. They can be monocyclic as in benzene, bicyclic as in naphthalene, or polycyclic as in anthracene. Simple monocyclic aromatic rings are usually five-membered rings like pyrrole or six-membered rings like pyridine. Fused aromatic rings consist of monocyclic rings that share their connecting bonds.
Dichloromethane
Natural sources of dichloromethane include oceanic sources, macroalgae, wetlands, and volcanoes. However, the majority of dichloromethane in the environment is the result of industrial emissions.
Chumash traditional medicine
Polycyclic aromatic hydrocarbons (PAHs) are a chemical product of fossil fuels, found in substances such as gasoline, tar, and cigarettes. The adverse health effects of PAHs are well-researched, perversely affecting the human body via the nervous system, hormonal disruptions, and fetal abnormalities.
Stilbene photocyclization
Stilbene photocyclization is the coupling of two aromatic carbons in stilbenes upon ultraviolet irradiation. The reaction can be used to form polycyclic aromatic hydrocarbons and heteroaromatics.
Polycyclic aromatic hydrocarbon
PAHs are abundant in the universe, and have recently been found to have formed possibly as early as the first couple of billion years after the Big Bang, in association with formation of new stars and exoplanets. Some studies suggest that PAHs account for a significant percentage of all carbon in the universe.
Aromaticity
The overwhelming majority of aromatic compounds are compounds of carbon, but they need not be hydrocarbons.
Perfume
Plants have long been used in perfumery as a source of essential oils and aroma compounds. These aromatics are usually secondary metabolites produced by plants as protection against herbivores, infections, as well as to attract pollinators. Plants are by far the largest source of fragrant compounds used in perfumery. The sources of these compounds may be derived from various parts of a plant. A plant can offer more than one source of aromatics, for instance the aerial portions and seeds of coriander have remarkably different odors from each other. Orange leaves, blossoms, and fruit zest are the respective sources of petitgrain, neroli, and orange oils.
Many modern perfumes contain synthesized odorants. Synthetics can provide fragrances which are not found in nature. For instance, Calone, a compound of synthetic origin, imparts a fresh ozonous metallic marine scent that is widely used in contemporary perfumes. Synthetic aromatics are often used as an alternate source of compounds that are not easily obtained from natural sources. For example, linalool and coumarin are both naturally occurring compounds that can be inexpensively synthesized from terpenes. Orchid scents (typically "salicylates") are usually not obtained directly from the plant itself but are instead synthetically created to match the fragrant compounds found in various orchids.
Cadalene
Cadalene or cadalin (4-isopropyl-1,6-dimethylnaphthalene) is a polycyclic aromatic hydrocarbon with a chemical formula CH and a cadinane skeleton. It is derived from generic sesquiterpenes, and ubiquitous in essential oils of many higher plants.
Asymmetric hydrogenation
The asymmetric hydrogenation of aromatic (especially heteroaromatic), substrates is a very active field of ongoing research. Catalysts in this field must contend with a number of complicating factors, including the tendency of highly stable aromatic compounds to resist hydrogenation, the potential coordinating (and therefore catalyst-poisoning) abilities of both substrate and product, and the great diversity in substitution patterns that may be present on any one aromatic ring. Of these substrates the most consistent success has been seen with nitrogen-containing heterocycles, where the aromatic ring is often activated either by protonation or by further functionalization of the nitrogen (generally with an electron-withdrawing protecting group). Such strategies are less applicable to oxygen- and sulfur-containing heterocycles, since they are both less basic and less nucleophilic; this additional difficulty may help to explain why few effective methods exist for their asymmetric hydrogenation.
Polycyclic aromatic hydrocarbon
In industrial countries, people who smoke tobacco products, or who are exposed to second-hand smoke, are among the most highly exposed groups; tobacco smoke contributes to 90% of indoor PAH levels in the homes of smokers. For the general population in developed countries, the diet is otherwise the dominant source of PAH exposure, particularly from smoking or grilling meat or consuming PAHs deposited on plant foods, especially broad-leafed vegetables, during growth. PAHs are typically at low concentrations in drinking water.
Emissions from vehicles such as cars and trucks can be a substantial outdoor source of PAHs in particulate air pollution. Geographically, major roadways are thus sources of PAHs, which may distribute in the atmosphere or deposit nearby. Catalytic converters are estimated to reduce PAH emissions from gasoline-fired vehicles by 25-fold.
Chalcogen
Oxygen's most common allotrope is diatomic oxygen, or O, a reactive paramagnetic molecule that is ubiquitous to aerobic organisms and has a blue color in its liquid state. Another allotrope is O, or ozone, which is three oxygen atoms bonded together in a bent formation. There is also an allotrope called tetraoxygen, or O, and six allotropes of solid oxygen including "red oxygen", which has the formula O.
Vinyl chloride
Vinyl chloride is an organochloride with the formula HC=CHCl that is also called vinyl chloride monomer (VCM) or chloroethene. This colorless compound is an important industrial chemical chiefly used to produce the polymer polyvinyl chloride (PVC). About 13 billion kilograms are produced annually. VCM is among the top twenty largest petrochemicals (petroleum-derived chemicals) in world production. The United States currently remains the largest VCM manufacturing region because of its low-production-cost position in chlorine and ethylene raw materials. China is also a large manufacturer and one of the largest consumers of VCM. Vinyl chloride is a gas with a sweet odor. It is highly toxic, flammable, and carcinogenic. It can be formed in the environment when soil organisms break down chlorinated solvents. Vinyl chloride that is released by industries or formed by the breakdown of other chlorinated chemicals can enter the air and drinking water supplies. Vinyl chloride is a common contaminant found near landfills. In the past VCM has been used as a refrigerant.
Polycyclic aromatic hydrocarbon
Two- and three-ringed PAHs can disperse widely while dissolved in water or as gases in the atmosphere, while PAHs with higher molecular weights can disperse locally or regionally adhered to particulate matter that is suspended in air or water until the particles land or settle out of the water column. PAHs have a strong affinity for organic carbon, and thus highly organic sediments in rivers, lakes, and the ocean can be a substantial sink for PAHs.
Aromatic hydrocarbon
The arene ring has an ability to stabilize charges. This is seen in, for example, phenol (CH–OH), which is acidic at the hydroxyl (OH), since a charge on this oxygen (alkoxide –O) is partially delocalized into the benzene ring.
Other monocyclic aromatic hydrocarbon include Cyclotetradecaheptaene or Cyclooctadecanonaene.
Polycyclic aromatic hydrocarbon
Most PAHs are insoluble in water, which limits their mobility in the environment, although PAHs sorb to fine-grained organic-rich sediments. Aqueous solubility of PAHs decreases approximately logarithmically as molecular mass increases.
Two-ringed PAHs, and to a lesser extent three-ringed PAHs, dissolve in water, making them more available for biological uptake and degradation. Further, two- to four-ringed PAHs volatilize sufficiently to appear in the atmosphere predominantly in gaseous form, although the physical state of four-ring PAHs can depend on temperature. In contrast, compounds with five or more rings have low solubility in water and low volatility; they are therefore predominantly in solid state, bound to particulate air pollution, soils, or sediments. In solid state, these compounds are less accessible for biological uptake or degradation, increasing their persistence in the environment.
Indenofluorene
Indenofluorenes (IFs) are members of the family of polycyclic hydrocarbons which incorporate a core Indene and a core Fluorene to form a 6-5-6-5-6 ring system. While IFs are members of the polycyclic hydrocarbon family, they are not necessarily members of the polycyclic aromatic hydrocarbon family. For example, the fully conjugated versions, shown below, have 20π electrons making them formally anti-aromatic. Depending on the way that the indene and fluorene are connected, five regioisomers can be formed where each regioisomer has unique properties, applications and extent of study.
Astrochemistry
Infrared astronomy has also revealed that the interstellar medium contains a suite of complex gas-phase carbon compounds called polyaromatic hydrocarbons, often abbreviated PAHs or PACs. These molecules, composed primarily of fused rings of carbon (either neutral or in an ionized state), are said to be the most common class of carbon compound in the galaxy. They are also the most common class of carbon molecule in meteorites and in cometary and asteroidal dust (cosmic dust). These compounds, as well as the amino acids, nucleobases, and many other compounds in meteorites, carry deuterium and isotopes of carbon, nitrogen, and oxygen that are very rare on earth, attesting to their extraterrestrial origin. The PAHs are thought to form in hot circumstellar environments (around dying, carbon-rich red giant stars).
Fulvic acid
Fulvic acids are of relatively low molecular mass and less biologically active than Humic Acids. 
Fulvic acid, one of two classes of natural acidic organic polymers that can be extracted from humus found in soil, sediment, or aquatic environments. Its name derives from Latin "fulvus", indicating its yellow colour. This organic matter is soluble in strong acid (pH = 1) and has the average chemical formula CHONS. A hydrogen-to-carbon ratio greater than 1:1 indicates less aromatic character (i.e., fewer benzene rings in the structure), while an oxygen-to-carbon ratio greater than 0.5:1 indicates more acidic character than in other organic fractions of humus (for example, humic acid, the other natural acidic organic polymer that can be extracted from humus). Its structure is best characterized as a loose assembly of aromatic organic polymers with many carboxyl groups (COOH) that release hydrogen ions, resulting in species that have electric charges at various sites on the ion. It is especially reactive with metals, forming strong complexes with Fe, Al, and Cu in particular and leading to their increased solubility in natural waters. Fulvic acid is believed to originate as a product of microbial metabolism, although it is not synthesized as a life-sustaining carbon or energy.
Bửu Hội
These involved the fundamental ring systems and derivatives of 1,2-benzanthracene, the dibenzopyrenes, steranthrenes, anthanthrene, 1,2,3,4-dibenzanthracene, a variety of benzo and dibenzofluoranthenes. This was extended to large-molecular-size and "hypercondensed" hydrocarbons, ring opening and partial hydrogenation. During his study of dibenzopyrenes, he discovered a molecular arrangement involving the framework of aromatic hydrocarbons. His studies of the carcinogenic azulenophenalenes led him to question the role of aromaticity. Aside from his studies with aza-replaced hydrocarbons, benz- and dibenzacridines and –carbazoles, he also synthesised and tested a number of new structural types of heteroaromatics with reference to the nature, nuimber and position of the heteroatoms. These included the naphtho and benzo derivatives of pyridocarbazole and beta-carboline, heteroaromatics with sulfur, arsenic or selenium replacements. These were either alone or in association with nitrogen, as well as sulfur and nitrogen containing pseudoazulenes. A series of hydrocarbon-like polynuclear lactones were explored with the intent of establishing a connection between polynuclear aromatics and aflatoxins. Such studies of heteroatomic polynuclears led him to propose a "newer picture" of a carcinogenic hydrocarbon, helping the generalise the classical K-region hypothesis.
Polycyclic aromatic hydrocarbon
A spectral database exists for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. Detection of PAHs in materials is often done using gas chromatography-mass spectrometry or liquid chromatography with ultraviolet-visible or fluorescence spectroscopic methods or by using rapid test PAH indicator strips.
Polycyclic aromatic hydrocarbon
Historically, PAHs contributed substantially to our understanding of adverse health effects from exposures to environmental contaminants, including chemical carcinogenesis. In 1775, Percivall Pott, a surgeon at St. Bartholomew’s Hospital in London, observed that scrotal cancer was unusually common in chimney sweepers and proposed the cause as occupational exposure to soot. A century later, Richard von Volkmann reported increased skin cancers in workers of the coal tar industry of Germany, and by the early 1900s increased rates of cancer from exposure to soot and coal tar was widely accepted. In 1915, Yamigawa and Ichicawa were the first to experimentally produce cancers, specifically of the skin, by topically applying coal tar to rabbit ears.
Polycyclic aromatic hydrocarbon
PAHs transform slowly to a wide range of degradation products. Biological degradation by microbes is a dominant form of PAH transformation in the environment. Soil-consuming invertebrates such as earthworms speed PAH degradation, either through direct metabolism or by improving the conditions for microbial transformations. Abiotic degradation in the atmosphere and the top layers of surface waters can produce nitrogenated, halogenated, hydroxylated, and oxygenated PAHs; some of these compounds can be more toxic, water-soluble, and mobile than their parent PAHs.
Polycyclic compound
In general, the term polycyclic includes polycyclic aromatic compounds, including polycyclic aromatic hydrocarbons, as well as heterocyclic aromatic compounds with multiple rings (where heteroaromatic compounds are aromatic compounds that contain sulfur, nitrogen, oxygen, or another non-carbon atoms in their rings in addition to carbon).
Hydroxyquinol
Hydroxyquinol is a common intermediate in the biodegradation of many aromatic compounds. These substrates include monochlorophenols, dichlorophenols, and more complex species such as the pesticide 2,4,5-T. Hydroxyquinol commonly occurs in nature as a biodegradation product of catechin, a natural phenol found in plants such as "Bradyrhizobium japonicum". Hydroxyquinol is also a metabolite in some organisms. For instance, Hydroxyquinol 1,2-dioxygenase is an enzyme that uses hydroxyquinol as a substrate with oxygen to produce 3-hydroxy-cis,cis-muconate.
Petroleum ether
The very lightest, most volatile liquid hydrocarbon solvents that can be bought from laboratory chemical suppliers may also be offered under the name petroleum ether. Petroleum ether consists mainly of aliphatic hydrocarbons and is usually low on aromatics. It is commonly hydrodesulfurized and may be hydrogenated to reduce the amount of aromatic and other unsaturated hydrocarbons. Petroleum ether bears normally a descriptive suffix giving the boiling range. Thus, from the leading international laboratory chemical suppliers it is possible to buy various petroleum ethers with boiling ranges such as 30-50 °C, 40-60 °C, 50-70 °C, 60-80 °C, etc. In the United States, laboratory grade aliphatic hydrocarbon solvents with boiling ranges as high as 100-140 °C may be called petroleum ether, rather than petroleum spirit.
Lac-Mégantic rail disaster
Environmentalists have reported heavy contamination from polycyclic aromatic hydrocarbons and believe arsenic levels to be well above legal limits.
Phospholipid-derived fatty acids
Phytoplankton (eukaryotic algae) are microscopic photosynthesizing plants that inhabit the sunlit layers of oceans and bodies of freshwater. As the primary source of elaborated carbon compounds, they are vital to the aquatic food web. Phytoplankton produce considerable amounts of polyunsaturated fatty acids (PUFA), including Eicosapentaenoic acid (EPA, 20:5 w3c), with microalgae being the origin of omega-3 fatty acids in fish oil. The diverse taxonomic groups in algae vary in abundance dependent on environmental conditions such as temperature, salinity, sunlight, and nutrient availability. The PLFA biomarker compositions were found to enable determination of the prevalence of the major groups in several marine environments. In a study of reservoir sedimentary deposits, an assumption was made that the community PUFA content constituted "ca". 50% of the total microeukaryotic PLFAs. It was also assumed that “The ratio of omega-3 to omega-6 fatty acids describes the relative contribution of phototrophic to heterotrophic members of the microeukaryotic community…”.
Astrobiology
Complex organic compounds of life, including uracil, cytosine and thymine, have been formed in a laboratory under outer space conditions, using starting chemicals such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), is the most carbon-rich chemical found in the universe.
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons are primarily found in natural sources such as creosote. They can result from the incomplete combustion of organic matter. PAHs can also be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal. PAHs are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources. The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other biofuels such as dung or crop residues contribute more than half of annual global PAH emissions, particularly due to biofuel use in India and China. As of 2004, industrial processes and the extraction and use of fossil fuels made up slightly more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States. Wildfires are another notable source. Substantially higher outdoor air, soil, and water concentrations of PAHs have been measured in Asia, Africa, and Latin America than in Europe, Australia, the U.S., and Canada.
Organic chemistry
Both saturated (alicyclic) compounds and unsaturated compounds exist as cyclic derivatives. The most stable rings contain five or six carbon atoms, but large rings (macrocycles) and smaller rings are common. The smallest cycloalkane family is the three-membered cyclopropane ((CH)). Saturated cyclic compounds contain single bonds only, whereas aromatic rings have an alternating (or conjugated) double bond. Cycloalkanes do not contain multiple bonds, whereas the cycloalkenes and the cycloalkynes do.
Propylene glycol methyl ether acetate
In the semiconductor industry, PGMEA is a commonly used solvent, primarily for the application of surface adherents such as Bis(trimethylsilyl)amine (HMDS) on silicon wafers. The compound is often the most abundant airborne, molecular contamination (AMC) in semiconductor cleanrooms, due to its evaporation into ambient air.
Humulene
Humulene, also known as α-humulene or α-caryophyllene, is a naturally occurring monocyclic sesquiterpene (CH), containing an 11-membered ring and consisting of 3 isoprene units containing three nonconjugated C=C double bonds, two of them being triply substituted and one being doubly substituted. It was first found in the essential oils of "Humulus lupulus" (hops), from which it derives its name. Humulene is an isomer of β-caryophyllene, and the two are often found together as a mixture in many aromatic plants.
Organic chemistry
The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a heterocycle. Pyridine and furan are examples of aromatic heterocycles while piperidine and tetrahydrofuran are the corresponding alicyclic heterocycles. The heteroatom of heterocyclic molecules is generally oxygen, sulfur, or nitrogen, with the latter being particularly common in biochemical systems.
Halorespiration
An ecologically significant aspect of bacterial halorespiration is the reduction of Polychloroethene (PCE) and Trichloroethene (TCE); anthropogenic pollutants with high neuro and hepatotoxicity. Their presence as environmental pollutants arose from their common industrial use as metal-degreasing agents from the 1920s - 1970. These xenobiotic compounds tend to form partially insoluble layers called dense non-aqueous phase liquids (DNAPLs) at the bottom of groundwater aquifers, which solubilize in a slow, reservoir-like manner, making TCE and PCE among the most common groundwater pollutants.
Mycobacterium vanbaalenii
Mycobacterium vanbaalenii is a rapidly growing mycobacterium that can use polycyclic aromatic hydrocarbons. It was first isolated from petroleum-contaminated estuarine sediments and has been shown by 16S rRNA gene sequencing to be closely related to "Mycobacterium aurum" and "Mycobacterium vaccae". "M. vanbaalenii" has potential use in the bioremediation of polycyclic aromatic hydrocarbon contaminated environmental sites. Etymology: vanbaalenii of Van Baalen, in memory of Dr Chase Van Baalen, late Professor at The University of Texas Marine Science Institute, Port Aransas Marine Laboratory, Port Aransas, TX, USA.
Polycyclic aromatic hydrocarbon
Multiple epidemiological studies of people living in Europe, the United States, and China have linked in utero exposure to PAHs, through air pollution or parental occupational exposure, with poor fetal growth, reduced immune function, and poorer neurological development, including lower IQ.
Pyrroline
Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic chemical compounds that differ in the position of the double bond. Pyrrolines are formally derived from the aromate pyrrole by hydrogenation. 1-Pyrroline is a cyclic imine, whereas 2-pyrroline and 3-pyrroline are cyclic amines.
9,10-Dihydroanthracene
9,10-Dihydroanthracene is an organic compound that is derived from the polycyclic aromatic hydrocarbon anthracene. Several isomers of dihydroanthracene are known, but the 9,10 derivative is most common. It is a colourless solid that is used as a carrier of H in various chemical reactions.
Medium-chain triglyceride
Medium-chain triglycerides (MCTs) are triglycerides with two or three fatty acids having an aliphatic tail of 6–12 carbon atoms, i.e., medium-chain fatty acids (MCFAs). Rich food sources for commercial extraction of MCTs include palm kernel oil and coconut oil.
Caryophyllene
Caryophyllene , or (−)-β-caryophyllene, is a natural bicyclic sesquiterpene that is a constituent of many essential oils, especially clove oil, the oil from the stems and flowers of "Syzygium aromaticum" (cloves), the essential oil of "Cannabis sativa", rosemary, and hops. It is usually found as a mixture with isocaryophyllene (the "cis" double bond isomer) and α-humulene (obsolete name: α-caryophyllene), a ring-opened isomer. Caryophyllene is notable for having a cyclobutane ring, as well as a "trans"-double bond in a 9-membered ring, both rarities in nature.
Polycyclic aromatic hydrocarbon
For example, in phenanthrene one Clar structure has two sextets—the first and third rings—while the other resonance structure has just one central sextet; therefore in this molecule the outer rings have greater aromatic character whereas the central ring is less aromatic and therefore more reactive. In contrast, in anthracene the resonance structures have one sextet each, which can be at any of the three rings, and the aromaticity spreads out more evenly across the whole molecule. This difference in number of sextets is reflected in the differing ultraviolet–visible spectra of these two isomers, as higher Clar pi-sextets are associated with larger HOMO-LUMO gaps; the highest-wavelength absorbance of phenanthrene is at 293 nm, while anthracene is at 374 nm. Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, and one in the first and fourth rings. Superposition of these structures reveals that the aromaticity in the outer rings is greater (each has a sextet in two of the three Clar structures) compared to the inner rings (each has a sextet in only one of the three).
Polycyclic aromatic compounds characteristically reduce to the radical anions. The redox potential correlates with the size of the PAH.
Polyglycolide
Polyglycolide or poly(glycolic acid) (PGA), also spelled as polyglycolic acid, is a biodegradable, thermoplastic polymer and the simplest linear, aliphatic polyester. It can be prepared starting from glycolic acid by means of polycondensation or ring-opening polymerization. PGA has been known since 1954 as a tough fiber-forming polymer. Owing to its hydrolytic instability, however, its use has initially been limited. Currently polyglycolide and its copolymers (poly(lactic-"co"-glycolic acid) with lactic acid, poly(glycolide-"co"-caprolactone) with ε-caprolactone and poly (glycolide-"co"-trimethylene carbonate) with trimethylene carbonate) are widely used as a material for the synthesis of absorbable sutures and are being evaluated in the biomedical field.
Polycyclic aromatic hydrocarbon
PAHs are typically found as complex mixtures. Lower-temperature combustion, such as tobacco smoking or wood-burning, tends to generate low molecular weight PAHs, whereas high-temperature industrial processes typically generate PAHs with higher molecular weights.
Urban runoff
Water running off these impervious surfaces tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from roadways and parking lots, as well as fertilizers and pesticides from lawns. Roads and parking lots are major sources of polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels, as well as of the heavy metals nickel, copper, zinc, cadmium, and lead. Roof runoff contributes high levels of synthetic organic compounds and zinc (from galvanized gutters). Fertilizer use on residential lawns, parks and golf courses is a measurable source of nitrates and phosphorus in urban runoff when fertilizer is improperly applied or when turf is over-fertilized.
Polycyclic aromatic hydrocarbon
PAHs are uncharged, non-polar molecules found in coal and in tar deposits. They are also produced by the thermal decomposition of organic matter (for example, in engines and incinerators or when biomass burns in forest fires).
Polycyclic aromatic hydrocarbon
Adult exposure to PAHs has been linked to cardiovascular disease. PAHs are among the complex suite of contaminants in tobacco smoke and particulate air pollution and may contribute to cardiovascular disease resulting from such exposures.
Aromaticity
Since the most common aromatic compounds are derivatives of benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word "aromatic" occasionally refers informally to benzene derivatives, and so it was first defined. Nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the double-ringed bases in RNA and DNA. An aromatic functional group or other substituent is called an aryl group.
Carboxylic acid
Carboxylic acids are Brønsted–Lowry acids because they are proton (H) donors. They are the most common type of organic acid.
Polyamine
A polyamine is an organic compound having more than two amino groups. Alkyl polyamines occur naturally but are also synthetic. Alkylpolyamines are colorless, hygroscopic, and water soluble. Near neutral pH, they exist as the ammonium derivatives. Most aromatic polyamines are crystalline solids at room temperature.
Aromatic hydrocarbon
Benzene, CH, is the simplest aromatic hydrocarbon, and it was the first one named as such. The nature of its bonding was first recognized by August Kekulé in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One goes to the hydrogen atom, and one to each of the two neighbouring carbons. This leaves one electron to share with one of the two neighbouring carbon atoms, thus creating a double bond with one carbon and leaving a single bond with the other, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon.
Methylcholanthrene
Methylcholanthrene is a highly carcinogenic polycyclic aromatic hydrocarbon produced by burning organic compounds at very high temperatures. Methylcholanthrene is also known as 3-methylcholanthrene, 20-methylcholanthrene or the IUPAC name 3-methyl-1,2-dyhydrobenzo[j]aceanthrylene. The short notation often used is 3-MC or MCA. This compound forms pale yellow solid crystals when crystallized from benzene and ether. It has a melting point around 180 °C and its boiling point is around 280 °C at a pressure of 80 mmHg. Methylcholanthrene is used in laboratory studies of chemical carcinogenesis. It is an alkylated derivative of benz["a"]anthracene and has a similar UV spectrum. The most common isomer is 3-methylcholanthrene, although the methyl group can occur in other places.
Polycyclic aromatic hydrocarbon
Low molecular weight PAHs, with two to four aromatic hydrocarbon rings, are more potent as co-carcinogens during the promotional stage of cancer. In this stage, an initiated cell (a cell that has retained a carcinogenic mutation in a key gene related to cell replication) is removed from growth-suppressing signals from its neighboring cells and begins to clonally replicate. Low-molecular-weight PAHs that have bay or bay-like regions can dysregulate gap junction channels, interfering with intercellular communication, and also affect mitogen-activated protein kinases that activate transcription factors involved in cell proliferation. Closure of gap junction protein channels is a normal precursor to cell division. Excessive closure of these channels after exposure to PAHs results in removing a cell from the normal growth-regulating signals imposed by its local community of cells, thus allowing initiated cancerous cells to replicate. These PAHs do not need to be enzymatically metabolized first. Low molecular weight PAHs are prevalent in the environment, thus posing a significant risk to human health at the promotional phases of cancer.