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. The most important reactions of this type that take place are aromatic nitration, aromatic halogenation, aromatic sulfonation, and acylation and alkylating Friedel-Crafts reactions. Organic reactions are chemical reactions between organic compounds. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... 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. ... In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. ... Nitration occurs with aromatic organic compounds via an electrophilic substitution mechanism involving the attack of the electron-rich benzene ring by the (nitryl) nitronium ion. ... In organic chemistry, an electrophilic aromatic halogenation is a type of halogenation. ... Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. ... The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. ...

Basic reactions

Aromatic nitrations to form nitro compounds take place by generating a nitronium ion from nitric acid and sulfuric acid. Nitration occurs with aromatic organic compounds via an electrophilic substitution mechanism involving the attack of the electron-rich benzene ring by the (nitryl) nitronium ion. ... Nitro compounds are organic compounds that contain one or more nitro functional groups (-NO2). ... The chemical compound nitric acid (HNO3), also known as aqua fortis and spirit of nitre, is an aqueous solution of hydrogen nitrate (anhydrous nitric acid). ... Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. ...

Aromatic sulfonation of benzene with fuming sulfuric acid gives benzenesulfonic acid. Image File history File links No higher resolution available. ... Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. ... Benzene is an organic chemical compound with the formula C6H6. ... Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. ...

Aromatic halogenation of benzene with bromine, chlorine or iodine gives the corresponding aryl halogen compounds catalyzed by iron tribromide. Image File history File links No higher resolution available. ... In organic chemistry, an electrophilic aromatic halogenation is a type of halogenation. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... Iron tribromide (also known as FeBr3, or Iron(III)Bromide) is a catalyst used in the aromatic halogenation of benzene. ...

The Friedel-Crafts reaction exists as an acylation and an alkylation with as reactants acyl halides or alkyl halides. Image File history File links No higher resolution available. ... The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. ... The haloalkanes (also known as Halogenoalkanes) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide. ...

The catalyst is always aluminium chloride. Image File history File links No higher resolution available. ... Aluminium chloride (AlCl3) is a compound of aluminium and chlorine. ...

Image File history File links No higher resolution available. ...

Other reactions

Other reactions that follow an electrophilic aromatic substitution pattern are a group of aromatic formylation reactions including the Vilsmeier-Haack reaction, the Gattermann Koch reaction and the Reimer-Tiemann reaction. Other electrophiles are aromatic diazonium salts in diazonium couplings, carbon dioxide in the Kolbe-Schmitt reaction and activated carbonyl groups in the Pechmann condensation. The Vilsmeier-Haack reaction or Vilsmeier reaction is an organic reaction between a substituted amide and a activated arene in the presence of phosphorus oxychloride. ... The Reimer-Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols. ... In chemistry, azo compounds generally have a molecular formula of the form R-N=N-R, in which R and R can be either aromatic or aliphatic. ... An azo coupling is an organic reaction between a diazonium compound and an aniline or a phenol. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms, and is in a gaseous state in the atmosphere of the Earth. ... The Kolbe-Schmitt reaction/Kolbe process (named after Adolph Wilhelm Hermann Kolbe and R. Schmitt) is a carboxylation chemical reaction that proceeds by heating sodium phenolate (the sodium salt of phenol) with carbon dioxide under pressure (100 atm, 125°C), then treating the product with sulfuric acid. ... Carbonyl group In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom : C=O. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e. ... The Pechmann condensation is a synthesis of coumarins, starting from a phenol and a carboxylic acid or ester containing a β-carbonyl group. ...

In the multistep Lehmstedt-Tanasescu reaction, one of the electrophiles is a N-nitroso intermediate. The Lehmstedt-Tanasescu reaction is a method in organic chemistry for the organic synthesis of acridone derivatives (3) from a 2-nitrobenzaldehyde (1) and an arene compound (2):[1][2][3][4][5] The reaction is named after two chemists who devoted part of their career to research into this...

Basic reaction mechanism

In the first step of the reaction mechanism for this reaction, the electrophile A is attacked by the electron-rich aromatic ring which in the simplest case is benzene. This leads to the formation of a positively-charged cyclohexadienyl cation, also known as an arenium ion. This carbocation is unstable, owing both to the positive charge on the molecule and to the temporary loss of aromaticity. However, the cyclohexadienyl cation is partially stabilized by resonance, which allows the positive charge to be distributed over three carbon atoms. In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. ... Benzene is an organic chemical compound with the formula C6H6. ... A cation is an ion with positive charge. ... Ball-and-stick model of the benzenium ion An arenium ion in organic chemistry is the cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. ... A carbocation (IPA pronunciation: ) is an ion with a positively-charged carbon atom. ... 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. ... Resonance in chemistry is a tool used to represent and model certain types of non-classical molecular structures. ...

In the second stage of the reaction, a Lewis base B donates electrons to the hydrogen atom at the point of electrophilic attack, and the electrons shared by the hydrogen return to the pi system, restoring aromaticity. Image File history File links No higher resolution available. ... A Lewis base is any molecule or ion that can form a new covalent bond by donating a pair of electrons. ...

An electrophilic substitution reaction on benzene does not always result in monosubstitution. While electrophilic substituents usually withdraw electrons from the aromatic ring and thus deactivate it against further reaction, a sufficiently strong electrophile can perform a second or even a third substitution. This is especially the case with the use of catalysts. A catalyst (Greek: καταλύτης) is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction (see also catalysis). ...

Substituted aromatic rings

Electrophiles may attack aromatic rings with functional groups. Performing an electrophilic substitution on an already substituted benzene compound raises the problem of regioselectivity. In case of a monosubstituted benzene, there are 4 different reactive positions. For a monosubstituted benzene, the ring carbon atom bearing the substituent is position 1 or ipso, the next ring atom is position 2 or ortho, position 3 is meta and position 4 is para. Positions 5 and 6 are respectively equal to 3 and 2. In organic chemistry, functional groups are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... In chemistry, regioselectivity is the preference of one direction of chemical bond making or breaking over all other possible directions. ... 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. ... 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. ... 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. ... 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. ... 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. ...

Substituents can generally be divided into two classes regarding electrophilic substitution: activating and deactivating towards the aromatic ring. Activating substituents or activating groups stabilize the cationic intermediate formed during the substitution by donating electrons into the ring system, by either inductive effect or resonance effects. Examples of activated aromatic rings are toluene, aniline and phenol. In organic chemistry, a functional group is called an activating group if a benzene molecule to which it is attached more readily participates in electrophilic substitution reactions. ... The inductive effect is associated with the dipole moment of the compound R-X. If X is at the negative end of a dipole moment, it will draw electrons from the ring and produce -I effect. ... Resonance structures are diagrammatic tools in organic chemistry to symbolize resonant bonds between atoms in molecules. ... 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. ... 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. ... Phenol, also known under an older name of carbolic acid, is a colourless crystalline solid with a typical sweet tarry odor. ...

The extra electron density delivered into the ring by the substituent is not equally divided over the entire ring, but is concentrated on atoms 2, 4 and 6 (the ortho and para positions). These positions are thus the most reactive towards an electron-poor electrophile. The highest electron density is located on both ortho positions, though this increased reactivity might be offset by steric hindrance between substituent and electrophile. The final result of the elecrophilic aromatic substitution might thus be hard to predict, and it is usually only established by doing the reaction and determining the ratio of ortho versus para substitution. Steric effects are the interaction of molecules dictated by their shape and/or spatial relationships. ...

On the other hand, deactivating substituents destabilize the intermediate cation and thus decrease the reaction rate. They do so by withdrawing electron density from the aromatic ring, though the positions most affected are again the ortho and para ones. This means that the most reactive positions (or, least unreactive) are the meta ones (atoms 3 and 5). Examples of deactivated aromatic rings are nitrobenzene, benzaldehyde and trifluoromethylbenzene. The deactivation of the aromatic system also means that generally harsher conditions are required to drive the reaction to completion. An example of this is the nitration of toluene during the production of trinitrotoluene (TNT). While the first nitration, on the activated toluene ring, can be done at room temperature and with dilute acid, the second one, on the deactivated nitrotoluene ring, already needs prolonged heating and more concentrated acid, and the third one, on very strongly deactivated dinitrotoluene, has to be done in boiling concentrated sulfuric acid. In organic chemistry, a deactivating group is a functional group attached to a benzene molecule that removes electron density from the benzene ring, making electrophilic aromatic substitution reactions slower and more complex relative to benzene. ... Iron rusting - a chemical reaction with a slow reaction rate. ... Nitrobenzene, also known as nitrobenzol or oil of mirbane, is a poisonous organic compound with an almond odor and chemical formula C6H5NO2. ... Benzaldehyde (C6H5CHO) is a chemical compound consisting of a benzene ring with an aldehyde substituent. ... Nitration is a general chemical process for the introduction of a nitro group in a chemical compound by means of a chemical reaction. ... 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. ... Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. ...

Functional groups thus usually tend to favor one or two of these positions above the others; that is, they direct the electrophile to specific positions. A functional group that tends to direct attacking electrophiles to the meta position, for example, is said to be meta-directing.

Ortho/para directors

Groups with unshared pairs of electrons, such as the amino group of aniline, are strongly activating and ortho/para-directing. Such activating groups donate those unshared electrons to the pi system. A lone pair is an electron pair without bonding or sharing with other atoms. ... In chemistry, especially in organic chemistry and biochemistry, an amino group is an ammonia-like functional group. ... 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. ... In organic chemistry, a functional group is called an activating group if a benzene molecule to which it is attached more readily participates in electrophilic substitution reactions. ...

When the electrophile attacks the ortho and para positions of aniline, the nitrogen atom can donate electron density to the pi system, giving four resonance structures (as opposed to three in the basic reaction). This substantially enhances the stability of the cationic intermediate. Compare this with the case when the electrophile attacks the meta position. Image File history File links No higher resolution available. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Resonance structures are diagrammatic tools in organic chemistry to symbolize resonant bonds between atoms in molecules. ...

In this case, the nitrogen atom cannot donate electron density to the pi system, giving only three resonance contributors. For this reason, the meta-substituted product is produced in much smaller proportion to the ortho and para products.

Other substituents, such as the alkyl and aryl substituents, may also donate electron density to the pi system; however, since they lack an available unshared pair of electrons, their ability to do this is rather limited. Thus they only weakly activate the ring and do not strongly disfavor the meta position. An alkyl is a univalent radical containing only carbon and hydrogen atoms arranged in a chain. ... In the context of organic molecules, aryl refers to any member of the set of functional groups or substituents that are derived from a simple aromatic ring. ... 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. ...

Halogens are ortho/para directors, since they possess an unshared pair of electrons just as nitrogen does. However, the stability this provides is offset by the fact that halogens are substantially more electronegative than carbon, and thus draw electron density away from the pi system. This destabilizes the cationic intermediate, and EAS occurs less readily. Halogens are therefore deactivating groups. Image File history File links No higher resolution available. ... The halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F, chlorine, Cl, bromine, Br, iodine, I, and astatine, At. ... It has been suggested that this article or section be merged with electronegativity. ... In organic chemistry, a deactivating group is a functional group attached to a benzene molecule that removes electron density from the benzene ring, making electrophilic aromatic substitution reactions slower and more difficult than they would be on benzene alone. ...

Directed ortho metalation is a special type of EAS with special ortho directors. Directed ortho metalation (DoM) is an adaptation of electrophilic aromatic substitution in which electrophiles attach themselves exclusively to the ortho- position of a direct metalation group or DMG through the intermediary of an aryllithium compound [1]. The DMG interacts with lithium through a hetero atom. ...

Meta directors

Non-halogen groups with atoms that are more electronegative than carbon, such as the nitro group (NO₂) draw substantial electron density from the pi system. These groups are strongly deactivating groups. Additionally, since the substituted carbon is already electron-poor, the resonance contributor with a positive charge on this carbon (produced by ortho/para attack) is less stable than the others. Therefore, these electron-withdrawing groups are meta directors. Nitro may refer to: Nitroglycerin, an extremely explosive chemical compound Nitrous, a type of fuel additive for race cars Nitromethane, another type of fuel additive for race cars [[GlyceryBold textl trinitrate (pharmacology)]], a medical compound used for the treatment of angina pectoris Nitrogen, especially when used in draught beer Nitrocellulose... In organic chemistry, a deactivating group is a functional group attached to a benzene molecule that removes electron density from the benzene ring, making electrophilic aromatic substitution reactions slower and more complex relative to benzene. ...

Ipso substitution

Ipso substitution is a special case of electrophilic aromatic substitution where the leaving group is not hydrogen.

A classic example is the reaction of salicylic acid with a mixture of nitric and sulphuric acid to form picric acid. The nitration of the 2 position involves the loss of CO₂ as the leaving group. Salicylic acid is the chemical compound with the formula C6H4(OH)CO2H, where the OH group is adjacent to the carboxyl group. ... The chemical compound nitric acid (HNO3), also known as aqua fortis and spirit of nitre, is an aqueous solution of hydrogen nitrate (anhydrous nitric acid). ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ...

Desulphonation in which a sulphonyl group is substituted by a proton is a common example.

Five membered heterocyclic compounds

Furan, Thiophene, Pyrrole and their derivatives are all highly activated compared to benzene. These compounds all contain an atom with an unshared pair of electrons (oxygen, sulfur, or nitrogen) as a member of the aromatic ring, which substantially increases the stability of the cationic intermediate. Examples of electrophilic substitutions to pyrrole are the Pictet-Spengler reaction and the Bischler-Napieralski reaction. Furan, also known as furane and furfuran, is a heterocyclic organic compound, produced when wood, especially pine-wood, is distilled. ... Thiophene is an aromatic heterocyclic compound consisting of four carbon atoms and one sulfur atom in a five-membered ring. ... Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H5N. Pyrroles are components of larger aromatic rings, including the porphyrins of heme, the chlorins and bacteriochlorins of chlorophyll, and the corrin ring of vitamin B12. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H5N. Pyrroles are components of larger aromatic rings, including the porphyrins of heme, the chlorins and bacteriochlorins of chlorophyll, and the corrin ring of vitamin B12. ... The Pictet-Spengler reaction is a chemical reaction in which a β-arylethylamine such as tryptamine is heated in the presence of an aldehyde and acid. ... The Bischler-Napieralski reaction is a chemical reaction that dehydrates an N-acyl β-arylethyl amines into the corresponding heterocycle. ...

External links

• Aromatic Substitution Reactions - MSU