'Arene' redirects here. For other uses, see.An aromatic hydrocarbon or arene (or sometimes aryl hydrocarbon) is a with and delocalized between carbon atoms forming a circle. In contrast, hydrocarbons lack this delocalization. The term 'aromatic' was assigned before the physical mechanism determining was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon,.

• Aromatic Hydrocarbons Toxicity
• Aromatic Hydrocarbons Examples
• Poly Aromatic Hydrocarbon

Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).Some non-benzene-based compounds called heteroarenes, which follow (for monocyclic rings: when the number of its π electrons equals 4 n + 2, where n = 0, 1, 2, 3.), are also called aromatic compounds. In these compounds, at least one carbon atom is replaced by one of the,. Examples of non-benzene compounds with aromatic properties are, a heterocyclic compound with a five-membered ring that includes a single oxygen atom, and, a heterocyclic compound with a six-membered ring containing one nitrogen atom. Main article:, C 6H 6, is the least complex aromatic hydrocarbon, and it was the first one named as such. The nature of its bonding was first recognized by 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.The structure is alternatively illustrated as a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This depiction represents the equivalent nature of the six carbon–carbon bonds all of 1.5; the equivalency is explained.

The electrons are visualized as floating above and below the ring with the electromagnetic fields they generate acting to keep the ring flat.General properties of aromatic hydrocarbons:. They display. The carbon–hydrogen ratio is high.

They burn with a strong sooty yellow flame because of the high carbon–hydrogen ratio. They undergo andThe circle symbol for aromaticity was introduced by 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 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.Arene synthesis A reaction that forms an arene compound from an unsaturated or partially unsaturated cyclic precursor is simply called an. Many laboratory methods exist for the of arenes from non-arene precursors. Many methods rely on reactions.

A detailed presentation of the nomenclature of aromatic hydrocarbons is. The names and structures of some of the simpler aromatic hydrocarbons are shown. Which of the compounds above (A-C) can undergo electrophilic addition. Aromatic Hydrocarbons Benzene, C 6 H 6, is the simplest member of a large family of hydrocarbons, called aromatic hydrocarbons. These compounds contain ring structures and exhibit bonding that must be described using the resonance hybrid concept of valence bond theory or the delocalization concept of molecular orbital theory.

Describes the 2+2+2 cyclization of three alkynes, in the an alkyne, carbon monoxide and a chromium carbene complex are the reactants. Of with or with expulsion of or carbon monoxide also form arene compounds. In the reactants are an plus a hydrogen donor.Another set of methods is the aromatization of and other aliphatic rings: reagents are catalysts used in such as platinum, palladium and nickel (reverse hydrogenation), and the elements. Arene reactions Arenes are reactants in many organic reactions.Aromatic substitution In aromatic substitution one on the arene ring, usually hydrogen, is replaced by another substituent. The two main types are when the active reagent is an electrophile and when the reagent is a nucleophile.

In the active reagent is a radical. An example of electrophilic aromatic substitution is the nitration of: Coupling reactions In a metal catalyses a coupling between two formal radical fragments. Common coupling reactions with arenes result in the formation of new e.g., alkylarenes, vinyl arenes, biraryls, new (anilines) or new (aryloxy compounds). An example is the direct arylation of Hydrogenation of arenes create saturated rings.

The compound is completely reduced to a mixture of -ol.The compound, hydrogenated with in presence of aqueous forms an which is alkylated with to 2-methyl-1,3-cyclohexandione: Cycloadditions reaction are not common. Unusual thermal Diels–Alder reactivity of arenes can be found in the. Other photochemical cycloaddition reactions with alkenes occur through.Dearomatization In the aromaticity of the reactant is permanently lost.Benzene and derivatives of benzene Benzene derivatives have from one to six attached to the central benzene core. Examples of benzene compounds with just one substituent are, which carries a group, and with a group. When there is more than one substituent present on the ring, their spatial relationship becomes important for which the ortho, meta, and para are devised. For example, three exist for because the methyl group and the hydroxyl group can be placed next to each other ( ortho), one position removed from each other ( meta), or two positions removed from each other ( para).

Has two methyl groups in addition to the hydroxyl group, and, for this structure, 6 isomers exist. Representative arene compounds.

Main article:(PAHs) are aromatic hydrocarbons that consist of fused and do not contain or carry. Is the simplest example of a PAH. PAHs occur in, and deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass). As pollutants, they are of concern because some compounds have been identified as,. PAHs are also found in cooked foods. Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish.They are also found in the, in, and in and are a. In the PAH motif is extended to large 2D sheets.See also.

Aromatic substituents:, and., a catalyst used to hydrogenate aromatic compounds.References. (the 'Gold Book') (1997). Online corrected version: (2006–) '.:. by Maria Backlund, Institute of Environmental Medicine, Karolinska Institutet. Armit, James Wilkins; (1925). 'Polynuclear heterocyclic aromatic types. Some anhydronium bases'.

127: 1604–1618. Jensen, William B. (April 2009). 86 (4): 423–424. (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley,. Webb, K.; Seneviratne, V. 'A mild oxidation of aromatic amines'.

Tetrahedron Letters. 36 (14): 2377–2378. Lafrance, M.; Rowley, C.; Woo, T.; Fagnou, K.

'Catalytic intermolecular direct arylation of perfluorobenzenes'. Journal of the American Chemical Society. 128 (27): 8754–8756. Meyers, A. I.; Beverung, W.

Aromatic Hydrocarbons Toxicity

N.; Gault, R. 51: 103.; Collective Volume, 6. Noland, Wayland E.; Baude, Frederic J. 41: 56.; Collective Volume, 5.

Fetzer, J. 'The Chemistry and Analysis of the Large Polycyclic Aromatic Hydrocarbons'.

Polycyclic Aromatic Compounds. New York: Wiley.

27 (2): 143. (PDF). European Commission, Scientific Committee on Food. December 4, 2002. Larsson, B. K.; Sahlberg, GP; Eriksson, AT; Busk, LA (1983). 'Polycyclic aromatic hydrocarbons in grilled food'.

31 (4): 867–873. Agency for Toxic Substances and Disease Registry. 1996.External links. Media related to at Wikimedia Commons.

Meador, in, 2008This article examines the ecotoxicological effects of polycyclic aromatic hydrocarbons (PAHs). The intent was to provide a general overview of the relevant ecotoxicological studies for these ubiquitous compounds and to provide basic information on environmental chemistry, sources, basic ecotoxicological methods, and important controlling factors for bioaccumulation and toxicity. The most critical determinants for PAH-specific bioaccumulation and toxicity include toxicokinetics (uptake and elimination kinetics), toxicodynamics (potency), biotransformation, and physicochemical properties. Photoactivation of PAHs and the potential for increased toxicity are also discussed in general terms and for specific taxa. All major toxicological responses known for PAHs are examined with most of the emphasis on sublethal effects, including adverse effects on growth, reproduction, development, the immune system, and resulting mutagenic effects. Most of the available data are for invertebrates and fish, which provide several examples and allow for generalizations across compounds. While far from exhaustive, relevant examples for birds, reptiles, amphibians, mammals, and plants are also provided.

Although few toxicology data exist for PAHs, information regarding water and sediment protection levels is included. Boehm, in, 1964 Publisher SummaryPolycyclic aromatic hydrocarbons (PAHs) are sometimes referred to as polynuclear aromatic hydrocarbons (PNAs), condensed ring aromatics, or fused ring aromatics. They are a class of organic compounds consisting of two or more fused aromatic rings. Polycyclic aromatic hydrocarbons most commonly encountered in the environment contain two (naphthalene) to seven (coronene) fused benzene rings, though PAHs with greater number of rings are also found. Natural sources of petrogenic PAHs arise from oil seepages and erosion of petroliferous shales, while natural sources of PAHs from combustion or pyrolysis include PAHs from incomplete combustion of wood and biomass via forest and grass fires.

Anthropogenic (pollution) related PAHs inputs can result in similar, but not identical, PAH compounds and assemblages of PAHs to those of natural origin. Anthropogenic inputs of PAH arise from the release into the environment of petrogenic PAHs through accidental acute petroleum spillages and through chronic non-point source and point-source inputs such as urban (storm water) runoff and municipal waste treatment plane discharges. The most common and ubiquitous sources of anthropogenic PAHs, however, are those associated with pyrogenic inputs. Polycyclic aromatic hydrocarbons (PAHs) are class of chemicals that can exist in more than 100 different combinations and are among the most ubiquitous pollutants in the natural environment. Many PAHs are considerably toxic to aquatic species, such as pyrene, which exhibits considerable toxicity even at low levels of exposure. 322 Furthermore, some are even carcinogenic, such as benzoapyrene. Consequently, 16 PAH compounds have been listed by the United States Environmental Protection Agency as pollutants of concern and consequently a value of 200 ng/l has been set as the maximum allowable limit in drinking water 123 ( Fig.

Ovalene, a PAH compound.PAHs are readily produced as a consequence of incomplete combustion of wood, tobacco and other fuel sources composed of carbon compounds. 330 Consequently, it is recognised that some PAHs in the environment can originate from natural sources, such as forest fires and volcano eruptions. 111 However, their presence in the environment is mainly due to anthropogenic activities, such as coal burning power plants, shipping activities 442 and refuse dumping sites. 441 Furthermore, some PAHs are used in industry to produce plastics, pesticides and dyes.Ocean-based industrial oil-extraction platforms regularly emit PAHs into the atmosphere as part of their manufacturing process, 363 while PAH by-products from combustion can be washed into marine habitats via rainfall and watercourses or settle from the atmosphere onto ocean surface waters.

444 Moreover, it has been determined that the burning of plastic refuse emits PAHs, with polystyrene producing the highest quantities. 450 Additionally, the manufacture of polystyrene can produce PAHs as an undesired consequence of incomplete polymerisation during processing in which the toxic PAH precursors, benzene and styrene, can become incorporated into the polymer matrix. 358The marine environment can also be directly polluted with PAHs due to the unintentional release of oil into seawater. 444 Interestingly, when analysing marine samples, the ratio between parent PAHs and alkylated PAHs can be used to determine whether the source of PAH contamination was of combustive origin or from petroleum-based fuels. 363 Accordingly, high levels of parent PAHs would equate to combustive emissions, such as the burning of oil and gas, while high levels of alkylated PAHs would represent contamination from petroleum products, such as fuel leakage during vessel activities in the region or from accidental spillages. Emsbo-Mattingly, Eric Litman, in, 2016 AbstractPolycyclic aromatic hydrocarbons (PAHs) are measured extensively to determine the nature and extent of oil spill impacts.

Conventional testing methods determine the concentrations of 16–34 PAH analytes for regulatory compliance and risk assessment. Recognizing the limited value of these data for source identification purposes, forensic investigators typically rely on a larger number of PAH analytes ( n = 49) with potential source specific associations. However, even these PAH analytes represent only a small fraction of the chemical fingerprinting potential imbedded in the 19,303 individual PAHs thought to exist in the semivolatile range. The absence of authentic PAH standards is one of the primary limitations for improving the testing methods. However, chemists recently expanded the number of quantitative forensic PAH analytes to include 37 additional parent and alkylated PAH isomers.

This method revision also provides qualitative chemical fingerprints from which the relative abundances of hundreds of additional PAH isomers are determined. In this chapter, the quantitative and qualitative fingerprints are presented for 12 reference samples that represent a wide range of hydrocarbon sources potentially encountered during oil spill investigations. The reference samples include crude oils, diesel, heavy gas oil, asphalt pavements, dielectric fluid, lube oil, tar, creosote, urban dust, and urban sediment.

A review of PAH weathering and source ratios demonstrate many options for differentiating petrogenic and pyrogenic releases. The ratios herein reflect past investigations described in the literature and the derivation of new ratios from the expanded list of PAH analytes. The updated method provides increased signature richness for distinguishing spilled oil from hydrocarbons derived from numerous other anthropogenic sources.

PAHs are semivolatile compounds under environmental conditions. They move between the atmosphere and the Earth’s surface in repeated, temperature-driven cycles of deposition and volatilization. In the presence of sunlight, PAHs undergo photooxidation in the ambient air, where they are present as vapors, or are absorbed into airborne particulate matter. Chemical breakdown of PAHs due to photooxidation can take several days to weeks; their presence in the atmosphere is subject to complex physicochemical reactions, photochemical transformations, and reactions with other pollutants.

The widespread occurrence of PAHs is largely due to their formation and release in all processes of incomplete combustion of organic materials. In the bottoms of aquatic systems, PAHs are adsorbed into particulates and precipitated or solubilized in any oily matter due to low solubility ( Figure 2.6). These persistent adsorbed PAHs later contaminate soil and water systems. Microbial populations in sediment/water systems degrade some PAHs and reduce their toxicity over a period of time. Aquatic organisms are mostly affected by PAH metabolism and photooxidation; the presence of UV light usually increases toxicity. PAHs enter into terrestrial animals by various routes, for example, inhalation, dermal contact, and ingestion, while absorption is the route of entry into plants from soil, that is, through their roots. Bioaccumulation of PAHs occurs in plants, although certain plant species can synthesize PAHs that act as growth hormones.

Since they are a moderate persistent contaminant in the environment, the concentration of PAHs in marine animals (fish and shellfish) is expected to be much higher than in the environment due to biomagnification. Fingas, in, 2017 10.13.3.6 Monitoring Polyaromatic Hydrocarbons on ParticulatesPAHs are aromatic compounds found in crude oil and are often produced as a result of combustion.

Many PAHs are toxic to man and the environment, particularly the larger PAHs. Crude oil burns result in PAH downwind of the fire, but the concentration on the particulate matter is often an order of magnitude less than the concentration in the starting oil and sometimes several orders of magnitude less.

Diesel contains low levels of PAHs with smaller molecular size but results in more PAHs of larger molecular sizes after burning. Larger PAHs are either created or concentrated by the fire. Larger PAHs, some of which are not even detectable in the diesel fuel, are found both in the soot and in the residue. The concentrations of these larger PAHs are low and often just above detection limits. Overall, studies have shown that more PAHs are destroyed by the fires than are created.The Soxhlet extraction method can be used to extract PAHs from the whole filter sheets more easily than microwave extraction 224.

Aromatic Hydrocarbons Examples

The extracts are dried by filtering through anhydrous sodium sulfate and concentrated to approximately 1–2 mL. The concentrated extracts are then quantitatively transferred to a preconditioned 1.5 g silica gel microcolumn topped with 1 cm anhydrous sodium sulfate for sample cleanup. The eluent is collected in a precalibrated centrifuge tube and concentrated under a stream of nitrogen to appropriate volume. Finally, the concentrated eluent is spiked with an internal standard d 14-terphenyl and made up to the accurate preinjection volume (0.5–1.0 mL) for GC analysis.The analysis of target PAHs and other hydrocarbons is performed on a gas chromatograph by a qualified laboratory. PAHs are ubiquitous and are natural pollutants of air, water, and soil. PAHs are mainly formed due to incomplete combustion of fossil fuels.

They are a usual component of dyes, plastics, and pesticides. Crude oil and coal deposits are natural repositories of PAHs. PAHs are composed of two or more fused aromatic rings. They are a class of multiphase compounds that are released into the environment naturally and by anthropogenic means.

Poly Aromatic Hydrocarbon

PAHs are one of the most significant classes of organic compounds that have caused rising concern regarding their harmful effects to humans and other living organisms. A total of 16 PAHs have been listed as toxic pollutants by the US EPA ( Perelo, 2010) ( Figure 8.2). They are highly hydrophobic in nature and tend to adsorb onto the surface of soil (or sediments in a marine environment). Wenning, Linda Martello, in, 2014 8.6.3 Environmental LevelsPAHs are ubiquitous environmental contaminants. Although they can be formed naturally (e.g. Forest fires), their predominant source is anthropogenic emissions, and the highest concentrations of PAH are generally found around urban centers. Concentrations of PAHs in the aquatic environment are generally highest in sediment, intermediate in biota and lowest in the water column 169.

Significant concentrations of PAH can be found in some major estuaries. However, PAH concentrations at offshore sites were generally low or undetectable. For sediments, while PAH concentrations are generally low or undetectable at most intermediate and offshore sites, further work should be concentrated on fine sediments and depositional areas.The main sources of PAHs in water bodies are atmospheric particulate matter deposition, runoff of polluted ground sources and pollution of river and lakes by industrial effluents, municipal wastewater discharge, and oil spills. Since PAHs have low solubility and tend to adsorb to particulate matter, they are usually found in low concentrations in water bodies. Some PAH concentrations that have been measured in water include: marine waters with levels of non-detected to 11 μg/L, wastewater in North American and European municipalities with levels of. Rosenfeld, Lydia G.H. Feng, in, 2011 15.4.2 Sources and ExposurePAHs can be found throughout the environment in soil, water, and air.

Sources that contribute to PAHs in the environment include vehicle exhausts, wildfires, agricultural burning, municipal and industrial waste incineration, and hazardous waste sites. The main pathways of exposure to PAHs are inhalation of the compounds in tobacco smoke, wood smoke, and ambient air, and consumption of PAHs in foods ( ATSDR, 1995). Those living near hazardous waste or industrial sites may be exposed to PAHs through contaminated air, water, and soil.

Exposure to PAHs can occur from eating foods that have grown in contaminated soil or air ( ATSDR, 1995; Phillips, 1999), or by cooking meat or other foods over an open flame, such as during grilling or charring ( Phillips, 1999). In addition, workers at facilities such as coal tar production plants, coking plants, asphalt production plants, coal-gasification sites, smoke houses, aluminum production plants, and municipal trash incinerators are exposed to PAHs ( ATSDR, 1995). Chemical structures of polycyclic aromatic hydrocarbons (PAHs) in ALH 84001. (A) Phenanthrene (C 14H 10); (B) pyrene (C 16H 10); (C) chrysene (C 18H 12); (D) perylene or benzopyrene (C 20H 12); (E) anthanthrene (C 22H 12); (F) dibenzothiophene (C 12H 8S).McKay et al. (1996) analyzed freshly broken fracture surfaces on small chips of ALH84001 for PAHs using a microprobe two-step laser mass spectrometer (μL 2MS).

The average PAH concentration on the surfaces was more than 1 ppm. Contamination checks and control experiments indicated that the observed organic material was from ALH84001. No PAHs in ALH84001 with intact fusion crust were present, and the PAH signal increased with increasing depth, becoming constant at approximately 1200 μm within the interior, well away from the fusion crust.The accumulation of PAHs on the Greenland ice sheet over the past 400 years has been studied in ice cores ( Kawamura and Suzuki, 1994).

The total concentration of PAHs in the cores varies from 10 ppt for preindustrial times to 1 ppb for recent snow deposition. Concentrations of PAHs in Antarctic ice were expected to lie between these two values. Analysis of Antarctic salt deposits on a heavily weathered meteorite (LEW 85320) by μL 2MS did not show the presence of terrestrial PAHs within detection limits, which suggested that the terrestrial contamination of PAHs for ALH84001 is less than 1%.The freshly broken but pre-existing fracture surfaces rich in PAHs also typically displayed carbonate globules.

The globules tend to be disc-shaped and flattened parallel to the fracture surface. Intact carbonate globules appeared orange in visible light and had a rounded appearance; many displaying alternating black and white rims. Under high magnification stereo light microscopy or SEM stereo imaging, some of the globules appear to be quite thin and pancake-like, suggesting that the carbonates formed in the restricted width of a thin fracture. This geometry limited their growth perpendicular to, but not parallel to, the fracture.The PAHs were highest in the carbonate-rich regions. Two groups of PAHs were identified from averaged mass spectra. A middle-mass group of 178–276 Da dominated, which was composed of simple 3- to 6-ring PAH skeletons. The alkylated homologs were less than 10% of the total signal intensity.

Principal peaks at 178, 202, 228, 252, and 278 Da were assigned to phenanthrene (C 14H 10; see Fig. 7.9A), pyrene (C 16H 10; see Fig. 7.9B), chrysene (C 18H 12; see Fig. 7.9C), perylene or benzopyrene (C 20H 12; see Fig.

7.9D), and anthanthrene (C 22H 12; see Fig. 7.9E).A second weak high-mass group of PAHs of about 300–450 Da was identified. The primary source of PAHs was anthropogenic emissions, which were characterized by the presence of abundant aromatic heterocycles, primarily dibenzothiophene (C 12H 8S; 184 Da; see Fig. The PAHs in ALH84001 were present at ppm levels but dibenzothiophene was not observed in any of the samples.