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Encyclopedia > Aromaticity

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. It can also be considered a manifestation of cyclic delocalization and of resonance.[1][2][3] Image File history File links This file was created by myself, and I hereby release it to public domain File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... A chemically conjugated system, is a system of atoms covalently bonded with alternating single and double bonds (e. ... “Covalent” redirects here. ... A lone pair is an electron pair without bonding or sharing with other atoms. ... An atomic orbital is a mathematical description of the region in which an electron may be found around a single atom. ... In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond. ... Resonance in chemistry is a tool used to represent and model certain types of non-classical molecular structures. ...


This is usually considered to be because electrons are free to cycle around circular arrangements of atoms, which are alternately single- and double-bonded to one another. These bonds may be seen as a hybrid of a single bond and a double bond, each bond in the ring identical to every other. This commonly-seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by Kekulé (see "History" section below). The model for benzene consists of two resonance forms, which corresponds to the double and single bonds' switching positions. Benzene is a more stable molecule than would be expected without accounting for charge delocalization. e- redirects here. ... For other uses, see Atom (disambiguation). ... Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or sometimes between atoms and other covalent bonds. ... Friedrich August Kekulé von Stradonitz Friedrich August Kekulé von Stradonitz (September 7, 1829 – July 13, 1896) was a German organic chemist. ... Benzene is an organic chemical compound with the formula C6H6. ... Resonance in chemistry is a tool used to represent and model certain types of non-classical molecular structures. ...

Contents

Theory

By convention, the double-headed arrow indicates that the two structures are simply hypothetical, since neither is an accurate representation of the actual compound. The actual molecule is best represented by a hybrid (average) of these structures, which can be seen at right. A C=C bond is shorter than a C−C bond, but benzene is perfectly hexagonal--all six carbon-carbon bonds have the same length, intermediate between that of a single and that of a double bond. Chemical structure of benzene Selfmade by cacycle Old version: File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In molecular geometry, bond length or bond distance is the distance between two bonded atoms in a molecule. ... Covalently bonded hydrogen and carbon in a molecule of methane. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ...


A better representation is that of the circular π bond (Armstrong's inner cycle), in which the electron density is evenly distributed through a π bond above and below the ring. This model more correctly represents the location of electron density within the aromatic ring. Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (Ï€ bonds) are chemical bonds of the covalent type, where two lobes of one involved electron orbital overlap two lobes of the other involved electron orbital. ...


The single bonds are formed with electrons in line between the carbon nuclei--these are called sigma bonds. Double bonds consist of a sigma bond and another bond--a π bond. The π-bonds are formed from overlap of atomic p-orbitals above and below the plane of the ring. The following diagram shows the positions of these p-orbitals: Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ bonds) are a type of covalent chemical bond. ... Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture. ... In chemistry, an atomic orbital is the region in which an electron may be found around a single atom. ...


Benzene electron orbitals Orbitals in benzene. ...


Since they are out of the plane of the atoms, these orbitals can interact with each other freely, and become delocalised. This means that instead of being tied to one atom of carbon, each electron is shared by all six in the ring. Thus, there are not enough electrons to form double bonds on all the carbon atoms, but the "extra" electrons strengthen all of the bonds on the ring equally. The resulting molecular orbital has π symmetry. In chemistry, a molecular orbital is a region in which an electron may be found in a molecule. ...


Benzene orbital delocalisation Benzene orbitals, cropped and translated from de:Bild:Benzol. ...


History

The first known use of the word "aromatic" as a chemical term -- namely, to apply to compounds that contain the phenyl radical -- occurs in an article by August Wilhelm Hofmann in 1855.[4] If this is indeed the earliest introduction of the term, it is curious that Hofmann says nothing about why he introduced an adjective indicating olfactory character to apply to a group of chemical substances, only some of which have notable aromas. Ironically, many of the most odoriferous organic substances known are terpenes, which are not aromatic in the chemical sense. But terpenes and benzenoid substances do have a chemical characteristic in common, namely higher unsaturation indexes than many aliphatic compounds, and Hofmann may not have been making a distinction between the two categories. In chemistry, the phenyl group or phenyl ring (often abbreviated as -Ph) is the functional group with the formula -C6H5 Picture where the six carbon atoms are arranged in a cyclic manner. ... Look up Radical in Wiktionary, the free dictionary. ... August Wilhelm von Hofmann (April 8, 1818 _ May 5, 1892) was a German chemist. ... Olfaction, the sense of smell, is the detection of chemicals dissolved in air (or, by animals that breathe water, in water). ... Terpenes are a class of hydrocarbons, produced by many plants, particularly conifers. ... In chemistry, aliphatic compounds are organic compounds in which carbon atoms are joined together in straight or branched chains. ...


The cyclohexatriene structure for benzene was first proposed by August Kekulé in 1865. Over the next few decades, most chemists readily accepted this structure, since it accounted for most of the known isomeric relationships of aromatic chemistry. However, it was always puzzling that this purportedly highly unsaturated molecule was so unreactive toward addition reactions. Benzene is an organic chemical compound with the formula C6H6. ... Kekulé von Stradonitz Friedrich August Kekulé von Stradonitz (September 7, 1829 – July 13, 1896) was a German organic chemist. ...


The discoverer of the electron J. J. Thomson, in 1921 placed three equivalent electrons between each carbon atom in benzene. Sir Joseph John Thomson, OM, FRS (18 December 1856 – 30 August 1940) usually known as J. J. Thomson, was a British scientist. ...

An explanation for the exceptional stability of benzene is conventionally attributed to Sir Robert Robinson, who was apparently the first (in 1925)[5] to coin the term aromatic sextet as a group of six electrons that resists disruption. Image File history File links I, the author, hereby donate this image to the public domain File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Sir Robert Robinson, (13 September 1886 – 8 February 1975), won the 1947 Nobel Prize in Chemistry [1] for his research on plant dyestuffs (anthocyanins) and alkaloids. ...


In fact, this concept can be traced further back, via Ernest Crocker in 1922,[6] to Henry Edward Armstrong, who in 1890, in an article entitled The structure of cycloid hydrocarbons, wrote the (six) centric affinities act within a cycle...benzene may be represented by a double ring (sic) ... and when an additive compound is formed, the inner cycle of affinity suffers disruption, the contiguous carbon-atoms to which nothing has been attached of necessity acquire the ethylenic condition.[7] Henry Edward Armstrong as a young man Henry Edward Armstrong (1848-1937) was born (and lived all his life) in Lewisham, a suburb of London. ...


Here, Armstrong is describing at least four modern concepts. Firstly, his "affinity" is better known nowadays as the electron, which was only to be discovered seven years later by J. J. Thomson. Secondly, he is describing electrophilic aromatic substitution, proceeding (thirdly) through a Wheland intermediate, in which (fourthly) the conjugation of the ring is broken. He introduced the symbol C centered on the ring as a shorthand for the inner cycle, thus anticipating Eric Clar's notation. Arguably, he also anticipated the nature of wave mechanics, since he recognized that his affinities had direction, not merely being point particles, and collectively having a distribution that could be altered by introducing substituents onto the benzene ring (much as the distribution of the electric charge in a body is altered by bringing it near to another body). e- redirects here. ... Sir Joseph John Thomson, OM, FRS (18 December 1856 – 30 August 1940) usually known as J. J. Thomson, was a British scientist. ... Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile. ... An arenium ion the cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution . ... A chemically conjugated system, is a system of atoms covalently bonded with alternating single and double bonds (e. ... The wave equation is an important partial differential equation which generally describes all kinds of waves, such as sound waves, light waves and water waves. ...


The quantum mechanical origins of this stability, or aromaticity, were first modelled by Hückel in 1931. He was the first to separate the bonding electrons in sigma and pi electrons. Fig. ... Erich Armand Arthur Joseph Hückel (August 9, 1896 - February 16, 1980) was a German physicist and physical chemist. ...


Characteristics of aromatic (Aryl) compounds

An aromatic compound contains a set of covalently-bound atoms with specific characteristics: Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or sometimes between atoms and other covalent bonds. ...

  1. A delocalized conjugated π system, most commonly an arrangement of alternating single and double bonds
  2. Coplanar structure, with all the contributing atoms in the same plane
  3. Contributing atoms arranged in one or more rings
  4. A number of π delocalized electrons that is even, but not a multiple of 4. This is known as Hückel's rule. Permissible numbers of π electrons include 2, 6, 10, 14, and so on
  5. Special reactivity in organic reactions such as electrophilic aromatic substitution and nucleophilic aromatic substitution

Whereas benzene is aromatic (6 electrons, from 3 double bonds), cyclobutadiene is not, since the number of π delocalized electrons is 4, which of course is a multiple of 4. The cyclobutadienide (2−) ion, however, is aromatic (6 electrons). An atom in an aromatic system can have other electrons that are not part of the system, and are therefore ignored for the 4n + 2 rule. In furan, the oxygen atom is sp2 hybridized. One lone pair is in the π system and the other in the plane of the ring (analogous to C-H bond on the other positions). There are 6 π electrons, so furan is aromatic. In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond. ... Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or sometimes between atoms and other covalent bonds. ... A set of points is said to be coplanar if and only if they lie on the same geometric plane. ... In organic chemistry, Hückels rule estimates whether a planar ring molecule will have aromatic properties. ... Organic reactions are chemical reactions involving organic compounds. ... Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, appended to 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. ... Cyclobutadiene is the smallest [n]-annulene ([4]-annulene), an extremely unstable hydrocarbon having a lifetime shorter than five seconds in the free state. ... Furan, also known as furane and furfuran, is a heterocyclic organic compound, produced when wood, especially pine-wood, is distilled. ...


Aromatic molecules typically display enhanced chemical stability, compared to similar non-aromatic molecules. The circulating π electrons in an aromatic molecule produce ring currents that oppose the applied magnetic field in NMR. The NMR signal of protons in the plane of an aromatic ring are shifted substantially further down-field than those on non-aromatic sp2 carbons. This is an important way of detecting aromaticity. By the same mechanism, the signals of protons located near the ring axis are shifted up-field. Planar monocyclic molecules containing 4n π electrons are called antiaromatic and are, in general, destabilized. Molecules that could be antiaromatic will tend to alter their electronic or conformational structure to avoid this situation, thereby becoming non-aromatic. For example, cyclooctatetraene (COT) distorts itself out of planarity, breaking π overlap between adjacent double bonds. Aromatic molecules are able to interact with each other in so-called π-π stacking: the π systems form two parallel rings overlap in a "face-to-face" orientation. Aromatic molecules are also able to interact with each other in an "edge-to-face" orientation: the slight positive charge of the substituents on the ring atoms of one molecule are attracted to the slight negative charge of the aromatic system on another molecule. A diagram of an aromatic ring current. ... NMR may refer to: Nuclear magnetic resonance, a phenomenon involving the interaction of atomic nuclei and external magnetic fields Nielsen Media Research, a U.S. company which measures TV, radio and newspaper audiences This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... Antiaromatic (or pseudoaromatic) molecules are cyclic systems containing alternating single and double bonds, where the pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart. ... Antiaromatic (or pseudoaromatic) molecules are cyclic systems containing alternating single and double bonds, where the pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart. ... 1,3,5,7-Cyclooctatetrene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. ... In supramolecular chemistry, an aromatic interaction (or Ï€-Ï€ interaction) is a noncovalent interaction between organic compounds containing aromatic moieties. ...


Many of the earliest-known examples of aromatic compounds, such as benzene and toluene, have distinctive pleasant smells. This property led to the term "aromatic" for this class of compounds, and hence to "aromaticity" being the eventually-discovered electronic property of them.


Aromatic compound classifications

The key aromatic hydrocarbons of commercial interest are benzene, toluene, ortho-xylene and para-xylene. About 35 million tonnes are produced worldwide every year. They are extracted from complex mixtures obtained by the refining of oil or by distillation of coal tar, and are used to produce a range of important chemicals and polymers, including styrene, phenol, aniline, polyester and nylon. Benzene is an organic chemical compound with the formula C6H6. ... 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. ... The term xylenes refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. ... C8H8 redirects here. ... Phenol, also known under an older name of carbolic acid, is a colourless crystalline solid with a typical sweet tarry odor. ... Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. ... SEM picture of a bend in a high surface area polyester fiber with a seven-lobed cross section Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. ... Nylon is a generic designation for a family of synthetic polymers first produced on February 28, 1935 by Wallace Carothers at DuPont. ...


Heterocyclics

In heterocyclic aromatics, one or more of the atoms in the aromatic ring is of an element other than carbon. This can lessen the ring's aromaticity, and thus (as in the case of furan) increase its reactivity. Other examples include pyridine, imidazole, pyrazole, oxazole, thiophene, and their benzannulated analogs (benzimidazole, for example). Heterocyclic compounds are substances which contain a ring structure as found in benzene and the aromatic compounds, or aromatic hydrocarbons, but in which other atoms than carbon, such as sulfur, oxygen or nitrogen are found as part of the ring. ... Furan, also known as furane and furfuran, is a 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 putrid odour. ... Imidazole is a heterocyclic aromatic organic compound. ... Pyrazole refers both to the class of simple aromatic ring organic compounds of the heterocyclic series characterized by a 5-membered ring structure composed of three carbon atoms and two nitrogen atoms in adjacent positions and to the unsubstituted parent compound. ... Oxazole is the parent compound for vast class of heteroaromatic compounds. ... Thiophene is an aromatic heterocyclic compound consisting of four carbon atoms and one sulfur atom in a five-membered ring. ... Benzimidazole is a heterocyclic aromatic organic compound. ...


Polycyclics

Polycyclic aromatic hydrocarbons (PAH) are molecules containing two or more simple aromatic rings fused together by sharing two neighboring carbon atoms (see also simple aromatic rings). Examples are naphthalene, anthracene and phenanthrene. An illustration of typical polycyclic aromatic hydrocarbons. ... 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. ... 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. ...


Substituted aromatics

Many chemical compounds contain simple aromatic rings in their structure. Examples are DNA which contains purine and pyrimidine, trinitrotoluene (TNT), acetylsalicylic acid (aspirin) and paracetamol. A chemical compound is a chemical substance of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition. ... 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. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. ... Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring [1]. It is isomeric with two other forms of diazine. ... 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. ... Aspirin, or acetylsalicylic acid (IPA: ), (acetosal) is a drug in the family of salicylates, often used as an analgesic (to relieve minor aches and pains), antipyretic (to reduce fever), and as an anti-inflammatory. ... 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. ...


Aromaticity in other systems

Aromaticity is found in ions as well: the cyclopropenyl cation (2e system), the cyclopentadienyl anion (6e system), the tropylium ion (6e) and the cyclooctatetraene dianion (10e). Aromatic properties have been attributed to non-benzenoid compounds such as tropone. Aromatic properties are tested to the limit in a class of compounds called cyclophanes. This article is about the electrically charged particle. ... --141. ... In organic chemistry, the tropylium ion is an aromatic species with a formula of [C7H7]+. Its name derives from the molecule tropane (itself named for the molecule atropine). ... 1,3,5,7-Cyclooctatetrene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. ... Tropone or 2,4,6-cycloheptatrien-l-on is an organic compound with some importance in organic chemistry as a non-benzenoid aromat. ... A cyclophane is a hydrocarbon consisting of an aromatic unit (typically a benzene ring) and an aliphatic chain that forms a bridge between two non-adjacent positions of the aromatic ring. ...


A special case of aromaticity is found in homoaromaticity where conjugation is interrupted by a single sp3 hybridized carbon atom. When carbon in benzene is replaced by other elements in borabenzene, silabenzene, germanabenzene, stannabenzene, phosphorine or pyrylium salts the aromaticity is still retained. Aromaticity is also not limited to compounds of carbon, oxygen and nitrogen. Homoaromaticity in organic chemistry is found in conjugated cyclic systems that are able to skip a part of the ring as opposed to regular aromaticity. ... four sp³ orbitals three sp² orbitals In chemistry, hybridisation or hybridization (see also spelling differences) is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. ... A borabenzene is a heteroaromatic compound that has a boron atom instead of the carbon atom of a benzene molecule. ... Silabenzene is a heteroaromatic compound containing a silicon atom instead of the carbon atom in benzene, so silabenzene has been one of the most interesting targets of theoretical and synthetic-organic chemists considering the question of whether heavy benzenes exhibit aromaticity. ... Germanabenzene (C5H6Ge) is the parent representative of a group of chemical compounds containing in their molecular structure a benzene ring with a carbon atom replaced by a germanium atom. ... Stannabenzene (C5H6Sn) is the parent representative of a group of chemical compounds containing in their molecular structure a benzene ring with a carbon atom replaced by a tin atom. ... Chemical structure of phosphorine Phosphorine is a heavy benzene containing a phosphorus atom instead of a CH moiety, so it is considered to be a heavier element analog of pyridine. ... 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. ...


Metal aromaticity is believed to exist in certain metal clusters of aluminium. Möbius aromaticity occurs when a cyclic system of molecular orbitals formed from pπ atomic orbitals and populated in a closed shell by 4n (n is an integer) electrons is given a single half-twist to correspond to a Möbius topology. Because the twist can be left-handed or right-handed, the resulting Möbius aromatics are dissymmetric or chiral. Up to now there is no doubtless proof, that a Möbius aromatic molecule was synthesized.[8][9] Aromatics with two half-twists corresponding to the paradromic topologies first suggested by Johann Listing have been proposed by Rzepa in 2005.[10] In carbo-benzene the ring bonds are extended with alkyne and allene groups. In Metal aromaticity the concept of aromaticity found in many hydrocarbons is extended to metals. ... In organic chemistry, Möbius aromaticity is a special type of aromaticity believed to exist in a number of organic molecules. ... An atomic orbital is the description of the behavior of an electron in an atom according to quantum mechanics. ... A Möbius strip, an object with only one surface and one edge; such shapes are an object of study in topology. ... People who are left-handed are more dextrous with their left hand than with their right hand: they will probably also use their left hand for tasks such as personal care, cooking, and so on. ... A person who is right-handed is more dextrous with their right hand than with their left hand: they will write with their right hand, and probably also use this hand for tasks such as personal care, cooking, and so on. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ... Johann Benedict Listing born July 25, 1808, died December 24, 1882 was a German mathematician, born in Frankfurt, Germany, and died in Göttingen, Germany. ... Henry S. Rzepa Prof Henry S. Rzepa Henry S. Rzepa is a contemporary computational organic chemist. ... A carbomer in organic chemistry is an expanded molecule obtained by insertion of a C2 unit in a given molecule [1]. Carbomers differ from their templates only in size but not in symmetry or energy when each C-C single bond is replaced by at least one alkyne bond and...


See also

An aromatic hydrocarbon (abbreviated as AH), or arene 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. ... An aromatic amine is an amine with an aromatic substituent - that is -NH2, -NH- or nitrogen group(s) attached to an aromatic hydrocarbon, whose structure usually contains one or more benzene rings. ... An illustration of typical polycyclic aromatic hydrocarbons. ... 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. ... In organic chemistry, Hückels rule estimates whether a planar ring molecule will have aromatic properties. ...

References

  1. ^ P. v. R. Schleyer, "Aromaticity (Editorial)", Chemical Reviews, 2001, 101, 1115-1118. DOI: 10.1021/cr0103221 Abstract.
  2. ^ A. T. Balaban, P. v. R. Schleyer and H. S. Rzepa, "Crocker, Not Armit and Robinson, Begat the Six Aromatic Electrons", Chemical Reviews, 2005, 105, 3436-3447. DOI: 10.1021/cr0103221 Abstract.
  3. ^ P. v. R. Schleyer, "Introduction: Delocalization-π and σ (Editorial)", Chemical Reviews, 2005, 105, 3433-3435. DOI: 10.1021/cr030095y Abstract.
  4. ^ A. W. Hofmann, "On Insolinic Acid," Proceedings of the Royal Society, 8 (1855), 1-3.
  5. ^ CCXI.—Polynuclear heterocyclic aromatic types. Part II. Some anhydronium bases James Wilson Armit and Robert Robinson Journal of the Chemical Society, Transactions, 1925, 127, 1604 - 1618 Abstract
  6. ^ APPLICATION OF THE OCTET THEORY TO SINGLE-RING AROMATIC COMPOUNDS Ernest C. Crocker J. Am. Chem. Soc.; 1922; 44(8) pp 1618 - 1630; Abstract
  7. ^ The structure of cycloid hydrocarbons Henry Edward Armstrong Proceedings of the Chemical Society (London), 1890, 6, 95 - 106 Abstract
  8. ^ Synthesis of a Möbius aromatic hydrocarbon D. Ajami, O. Oeckler, A. Simon, R. Herges, Nature; 2003; 426 pp 819.
  9. ^ Investigation of a Putative Möbius Aromatic Hydrocarbon. The Effect of Benzannelation on Möbius [4 n]Annulene Aromaticity Claire Castro, Zhongfang Chen, Chaitanya S. Wannere, Haijun Jiao, William L. Karney, Michael Mauksch, Ralph Puchta, Nico J. R. van Eikema Hommes, Paul von R. Schleyer J. Am. Chem. Soc.; 2005; 127(8) pp 2425-2432 Abstract
  10. ^ A Double-Twist Möbius-Aromatic Conformation of [14]Annulene Henry S. Rzepa Org. Lett.; 2005; 7(21) pp 4637 Abstract

  Results from FactBites:
 
C&EN: SCIENCE & TECHNOLOGY - A Deeper Discussion Of All-Metal Aromaticity-Antiaromaticity (1089 words)
aromaticity, meaning that overall, the compound is aromatic.
Therefore, it's the aromaticity from the lone pairs that overwhelms the paramagnetic contributions from the antiaromatic
MOs of aromatic molecules are lower than the p orbital energy of the free atom.
Aromaticity - Hückel's rule, Aromatic ions (1232 words)
Aromaticity has to do with the unusual stability of the compound benzene and its derivatives, as well as certain other unsaturated ring compounds.
The aromaticity of the benzene ring can be assessed by measuring its "resonance energy." One way to do this is by measuring its heat of hydrogenation.
Although aromatic rings are normally planar, with uninterrupted conjugation, that is not always the case.
  More results at FactBites »

 
 

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