An aromatic hydrocarbon (abbreviated as AH) or arene ^[1] is a hydrocarbon, the molecular structure of which incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent. This sweet scent actually came from impurities in the compounds (which are not actually aromatic in the sense initially described). The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible aromatic hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic or polycyclic. Hydrocarbons are refined at oil refineries and processed at chemical plants A hydrocarbon is a chemical compound that consists only of the elements carbon (C) and hydrogen (H). ... Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond. ... Covalent bonding is a description of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. ... Benzene, C6H6, PhH, or benzol is a colorless and flammable liquid with a pleasant, sweet smell. ... In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ... Benzene, also known as benzol, is an organic chemical compound with the formula C6H6. ...

Note: Some non-benzene-based compounds which follow Hückel's rule are also aromatic compounds. Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring which includes an oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom.^[2]
In organic chemistry, Hückels rule estimates whether a planar ring molecule will have aromatic properties. ... Furan, also known as furane and furfuran, is an aromatic heterocyclic organic compound, produced when wood, especially pine-wood, is distilled. ... Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively sour odour. ...

Benzene ring model

Benzene

Main article: aromaticity

Benzene, C₆H₆, is the simplest AH and was recognized as the first aromatic hydrocarbon, with the nature of its bonding first being recognized by Friedrich August Kekulé von Stradonitz in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One goes to the hydrogen atom, and one each to the two neighboring carbons. This leaves one to share with one of its two neighboring carbon atoms, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon. Chemical structure of benzene Selfmade by cacycle File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Chemical structure of benzene Selfmade by cacycle File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Benzene, also known as benzol, is an organic chemical compound with the formula C6H6. ... Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. ... Benzene, also known as benzol, is an organic chemical compound with the formula C6H6. ... Friedrich August Kekulé von Stradonitz Friedrich August Kekulé von Stradonitz (September 7, 1829 – July 13, 1896) was a German organic chemist. ...

Many chemists draw a circle around the inside of the ring to show that there are six electrons floating around in delocalized molecular orbitals the size of the ring itself. This also accurately represents the equivalent nature of the six bonds all of bond order ~1.5. This equivalency is well explained by resonance forms. The electrons float above and below the ring, and the electromagnetic fields they generate keep the ring flat. General properties: Bond order is the number of bonds between a pair of atoms. ... Resonance structures of Benzene Resonance structures are diagrammatic tools used predominately in organic chemistry to symbolize resonant bonds between atoms in molecules. ...

1. Display aromaticity.
2. The Carbon-Hydrogen ratio is very large.
3. They burn with a sooty yellow flame because of the high carbon-hydrogen ratio.
4. They undergo electrophilic substitution reactions and nucleophilic aromatic substitutions.

Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. ... An electrophilic aromatic substitution is a chemical reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile. ... A nucleophilic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide on an aromatic ring. ...

Arene synthesis

Many laboratory methods exist for the organic synthesis of arenes from non-arene precursors: Organic synthesis is the construction of organic molecules via chemical processes. ...

• Alkyne trimerization, [2+2+2] cyclization of three alkynes
• Dötz reaction
• Diels-Alder reactions of alkynes with pyrone or cyclopentadienone with expulsion of carbon dioxide or carbon monoxide.
• Aromatization of cyclohexanes and other aliphatic rings: reagents are, catalysts used in hydrogenation such as platinum, palladium and nickel (reverse hydrogenation), quinones and the elements sulfur and selenium ^[3].
• Bergman cyclization, enyne plus hydrogen donor

An alkyne trimerisation reaction is a [2+2+2] cyclization reaction where three alkyne molecules react to form a benzene compound. ... The Dötz reaction is the chemical reaction of an aromatic or vinylic alkoxy pentacarbonyl chromium carbene complex with an alkyne and carbon monoxide to give a Cr(CO)3-coordinated substituted phenol. ... The Diels-Alder reaction The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. ... Alkynes are hydrocarbons that have at least one triple bond between two carbon atoms. ... A pyrylium compound is a conjugated 6 membered carbon ring system with one carbon atom replaced by a positively charged oxygen atom forming a salt with a negatively charged counterion [1]. It is the oxygen pendant of benzene and shares with it aromatic properties. ... Cyclohexane is a cycloalkane with the molecular formula C6H12. ... Hydrogenation is a class of chemical reactions in which the net result is an addition of hydrogen. ... A quinone (or benzoquinone) is either one of the two isomers of cyclohexadienedione or a derivative thereof. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ... Se redirects here. ... The Bergman cyclization or Bergman reaction or Bergman cycloaromatization is an organic reaction and more specifically a rearrangement reaction taking place when an enyne is heated in presence of a suitable proton donor (Scheme 1). ...

Arene reactions

The main arene reactions are:

• Electrophilic aromatic substitution
• Nucleophilic aromatic substitution
• Many coupling reactions to biraryls
• Hydrogenation to saturated rings

Lesser known reactions: Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, in an aromatic system is replaced by an electrophile. ... A nucleophilic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide on an aromatic ring. ... A coupling reaction in organic chemistry is a catch-all for a range of reactions in Organometallic chemistry where two hydrocarbon radicals are coupled with the aid of a metal containing catalyst. ... Hydrogenation is a class of chemical reactions in which the net result is an addition of hydrogen. ...

• Unusual thermal Diels-Alder reactivity of arenes can be found in the Wagner-Jauregg reaction
• Other photochemical cycloaddition reactions with alkenes through excimers.

The Wagner-Jauregg reaction is a classic organic reaction in organic chemistry (named after its inventors) describing the Diels-Alder reaction of 2 equivalents of maleic anhydride with a 1,1-diarylethylene. ... Excimer energy diagram An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. ...

Benzene and derivatives of benzene

Toluene

Benzene derivatives have from one to six substituents attached to the central benzene core. Examples of benzene compounds with just one substituent are phenol which carries a hydroxyl group and toluene with a methyl group. When there is more than one substituent present on the ring their spatial relationship becomes important for which the arene substitution patterns ortho, meta and para are devised. For example three isomers exist for cresol 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). Xylenol has two methyl groups in addition to the hydroxyl group and for this structure 6 isomers exist. from meta This image is ineligible for copyright and therefore in the public domain, because it consists entirely of information that is common property and contains no original authorship. ... from meta This image is ineligible for copyright and therefore in the public domain, because it consists entirely of information that is common property and contains no original authorship. ... Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene. ... In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. ... Phenol, also known under an older name of carbolic acid, is a colourless crystalline solid with a typical sweet tarry odor. ... // Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene. ... In chemistry a methyl-group is a hydrophobic Alkyl functional group which is derived from methane (CH4). ... Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ... In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of bonds between atoms, but in which the atoms are arranged differently. ... Cresols are organic chemical compounds which are methylphenols. ... Xylenol or dimethylphenol is a benzene derivative with two methyl groups and a hydroxyl group. ...

Examples of benzene derivative with alkyl substituents (alkylbenzenes) are:

• Ethylbenzene C₆H₅-CH₂-CH₃
• Mesitylene C₆H₃(-CH₃)₃
• Toluene C₆H₅-CH₃
• Xylene C₆H₄(-CH₃)₂

Examples of other aromatic compounds: Chemical Structure of Ethylbenzene Ethylbenzene is an organic chemical compound which is an aromatic hydrocarbon with the chemical formula C8H10. ... In organic chemistry, mesitylene or 1,3,5-trimethylbenzene (C9H12) is an aromatic hydrocarbon with three methyl substituents attached to the benzene ring. ... Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene. ... The term xylenes refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. ...

• Aniline C₆H₅-NH₂
• Acetylsalicylic acid C₆H₄(-O-C(=O)-CH₃)(-COOH)
• Benzoic acid C₆H₅-COOH
• Biphenyl (C₆H₅)₂
• Chlorobenzene C₆H₅-Cl
• Nitrobenzene C₆H₅-NO₂
• Paracetamol C₆H₄(-NH-C(=O)-CH₃)(-OH)
• Phenacetin C₆H₄(-NH-C(=O)-CH₃)(-O-CH₂-CH₃)
• Phenol C₆H₅-OH
• Picric acid C₆H₂(-OH)(-NO₂)₃
• Salicylic acid C₆H₄(-OH)(-COOH)
• Trinitrotoluene C₆H₂(-CH₃)(-NO₂)₃

The arene ring has an ability to stabilize charges. This is seen in, for example, phenol (C₆H₅-OH), which is acidic at the hydroxyl (OH), since a charge on this oxygen (alkoxide -O^–) is partially delocalized into the benzene ring. Aniline, phenylamine or aminobenzene (C6H5NH2) is an organic chemical compound which is a primary aromatic amine consisting of a benzene ring and an amino group. ... A very old bottle of Aspirin Aspirin or acetylsalicylic acid is a drug in the family of salicylates, often used as an analgesic (against minor pains and aches), antipyretic (against fever), and anti-inflammatory. ... Benzoic acid, C7H6O2 (or C6H5COOH), is a colorless crystalline solid and the simplest aromatic carboxylic acid. ... Biphenyl (or Diphenyl or 1,1-Biphenyl or lemonene) is a solid compound that forms colourless to yellowish crystals. ... Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. ... Nitrobenzene, also known as nitrobenzol or oil of mirbane, is a poisonous organic compound with an almond odor and chemical formula C6H5NO2. ... Paracetamol (INN) (IPA: ) or acetaminophen (USAN), is a common analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains. ... Phenacetin, introduced in 1887, is used principally as an analgesic. ... Phenol, also known under an older name of carbolic acid, is a colourless crystalline solid with a typical sweet tarry odor. ... Picric acid is the common term for the chemical compound 2,4,6-trinitrophenol, also known as TNP; the material is a yellow crystalline solid. ... Salicylic acid is the chemical compound with the formula C6H4(OH)CO2H, where the OH group is adjacent to the carboxylic acid group. ... R-phrases S-phrases Related Compounds Related compounds picric acid hexanitrobenzene Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Trinitrotoluene (TNT) is a chemical compound with the formula C6H2(NO2)3CH3. ... For alternative meanings see acid (disambiguation). ...

Polycyclic aromatic hydrocarbons

Main article: Polycyclic aromatic hydrocarbon

Naphthalene

Some important arenes are the polycyclic aromatic hydrocarbons (PAH); they are also called polynuclear aromatic hydrocarbons. They are composed of more than one aromatic ring. The simplest PAH is benzocyclobutene (C₈H₆). An illustration of typical polycyclic aromatic hydrocarbons - NASA Crystal structure of a hexa-peri-hexabenzocoronene reported by Müllen and cooworkers in Chem. ... from meta File links The following pages link to this file: Aromatic hydrocarbon Categories: GFDL images ... from meta File links The following pages link to this file: Aromatic hydrocarbon Categories: GFDL images ... Naphthalene (not to be confused with naphtha) (also known as naphthalin, naphthaline, tar camphor, white tar, albocarbon, or naphthene), is a crystalline, aromatic, white, solid hydrocarbon, best known as the primary ingredient of mothballs. ... Benzocyclobutene (BCB) is the simplest polycyclic aromatic hydrocarbon, being composed of a benzene ring fused to a cyclobutene ring. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... This article is about the chemistry of hydrogen. ...

Common examples are Naphthalene, Anthracene, Phenanthrene and triphenylene. More exotic examples are helicenes and Corannulene. Naphthalene (not to be confused with naphtha) (also known as naphthalin, naphthaline, tar camphor, white tar, albocarbon, or naphthene), is a crystalline, aromatic, white, solid hydrocarbon, best known as the primary ingredient of mothballs. ... In chemistry, anthracene is a solid polycyclic aromatic hydrocarbon consisting of three benzene rings derived from coal-tar. ... Phenanthrene is a polycyclic aromatic hydrocarbon composed of three fused benzene rings--as the above formula shows. ... In chemistry, triphenylene is the name of an organic compound. ... [6]helicene In organic chemistry, helicenes are ortho-condensed polycyclic aromatic compounds in which benzene rings are angularly annulated so as to give helically shaped molecules. ... Corannulene is a polycyclic aromatic hydrocarbon with chemical formula C20H10 . ...

See also

• Simple aromatic rings

Simple aromatic rings are aromatic organic compounds (also known as arenes or aromatics) that consist only of conjugated planar ring systems with delocalized pi electron clouds instead of discrete alternating single and double bonds. ...

External links

• R. H. Logan's homepage: Aromaticity And Aromatic Hydrocarbons
• Carcinogenic FAC list in Portable Document Format.
• Toxicological profiles of PAH.
• LIST of PAH.
• Abiogenic Gas Debate 11:2002 (EXPLORER)

Portable Document Format (PDF) is an open file format created by Adobe Systems in 1993 and is now being prepared for submission as an ISO standard[1]. It is for representing two-dimensional documents in a device independent and resolution independent fixed-layout document format. ...

References

1. ^ Definition IUPAC Gold Book Link
2. ^ HighBeam Encyclopedia: aromatic compound
3. ^ Jerry March Advanced Organic Chemistry 3Ed., ISBN 0-471-85472-7