Cowardly. 22.4: Electrophilic aromatic substitution (2023)

  1. Recently updated
  2. save as PDF
  • Minor ID
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!- \!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{ span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart }{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\ norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm {span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\ mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{ \ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{ \unicode[.8,0]{x212B}}\)

    scope and mechanism

    In this section we are mainly interested in the reactions of arenes that attack the carbon atoms of the aromatic ring. We will not now go into the reactions of the substituent groups around the ring.

    The main types of reactions involving aromatic rings are substitution, addition, and oxidation. The most common type of this is electrophilic substitution. An overview of the most important benzene substitution reactions is shown in Figure 22.7. Many of the reagents used for these substitutions are familiar to you in connection with electrophilic addition reactions to alkenes (e.g. \(\ce{Cl_2}\), \(\ce{Br_2}\), \(\ce{ H_2SO_4}\ ) and \(\ce{HOCl}\);§ 10-3). Electrophilic addition to alkenes and electrophilic aromatic substitution are polar step processes, and the key step in each is attack of the electrophile on the carbon to form a cationic intermediate. We can represent this type of reaction by the following general equations, where the attacking reagent is represented either formally as a cation, \(\ce{X}^\ominus\), or as a neutral but polarized molecule, \(\ omitted {\delta \oplus }{\ce{X}}\)---\(\overset{\delta \ominus }{\ce{Y}}\):

    electrophilic aromatic substitution(first step)

    Cowardly. 22.4: Electrophilic aromatic substitution (2)

    Elektrophile Addition an Alkene(first step)

    Cowardly. 22.4: Electrophilic aromatic substitution (3)

    Cowardly. 22.4: Electrophilic aromatic substitution (4)

    The intermediate product presented as an aromatic substitution no longer has an aromatic structure; Rather, it is a cation with four \(\pi\) electrons distributed over five carbon nuclei, with the sixth carbon being saturated with \(sp^3\) hybrid bonds. It can be formulated in terms of the following component structures, which are assumed to make roughly the same contribution:

    Cowardly. 22.4: Electrophilic aromatic substitution (5)

    How important it is to write a hybrid structure with partial charges at these three positions will become clear later. This type of ion is referred to as\(\sigma\) connectionDieBenzolion.

    The aromatic ring is regenerated from this cationic intermediate by loss of a proton from the hybridized carbon \(sp^3\). The electron pair in this bond \(\ce{C-H}\) then becomes part of the aromatic \(\pi\)-electron system and a benzene substitution product is formed, \(\ce{C_6H_5X}\).

    electrophilic aromatic substitution(second step)

    Cowardly. 22.4: Electrophilic aromatic substitution (6)

    The increase in stabilization associated with the regeneration of the aromatic ring is so favorable that it is usually the preferred course of the reaction and not the combination of the cation with \(\ce{Y}^\ominus\). This is the difference between aromatic substitution and alkene addition. In the case of alkenes, the loss of a proton from an intermediate does not typically yield significant resonance energy, so it tends to react when combined with a nucleophilic reagent.

    Elektrophile Addition an Alkene(second step)

    \[\overset{\oplus}{\ce{C}} \ce{H_2-CH_2X} + \ce{Y}^\ominus \rightarrow \ce{YCH_2-CH_2X}\]

    The type of replacement factor

    It is important to know that in aromatic substitution the actual electrophilic substituent \(\overset{\oplus}{\ce{X}}\) or \(\overset{\delta \oplus}{\ce{X } } } } - \overset{\delta \ominus }{\ce{Y}}\) does not necessarily mean the reagent added to the reaction mixture. For example, nitration in mixtures of nitric acid and sulfuric acid is not caused by attack of the nitric acid molecule on the aromatic compound, but by attack of the more electrophilic compound, the nitronium ion, \(\ce{NO_2^+). }\ ). This ion is formed from nitric acid and sulfuric acid according to the following equation:

    \[\ce{HNO_3} + 2 \ce{H_2SO_4} \rightleftharpoons \ce{NO_2^+} + \ce{H_3O^+} + 2 \ce{HSO_4^-}\]

    The nitronium ion attacks the aromatic ring, producing first the nitrobenzene ion and then the aromatic nitro compound:

    Cowardly. 22.4: Electrophilic aromatic substitution (7)

    In general, the function of the catalyst (so often required to promote aromatic substitution) is to generate an electrophilic substituting agent from the given reagents. Therefore, with each substitution reaction, careful thought must be given to which substitution agent it might actually be. This problem does not arise to the same degree in electrophilic additions to alkenes, since alkenes are so much more reactive than arenes that the reagents used (e.g. \(\ce{Br_2}\), \(\ce{Cl_2}\ ), \(\ce{HCl}\), \(\ce{HOCl}\), \(\ce{HOBr}\), \(\ce{H_3O}^\oplus\)) are sufficiently electrophilic to to react with alkenes without the aid of a catalyst. In fact, conditions that lead to arene substitution, such as nitration in mixtures of nitric and sulfuric acids, often result in degradation of the alkene carbon skeleton.

    We now consider each of the substitution reactions shown in Figure 22-1 in terms of the nature of the substituent and its suitability for the synthesis of different classes of aromatic compounds.


    The nitronium ion, \(\ce{NO_2^+}\), is the active nitrating agent in mixtures of nitric and sulfuric acids. The nitration of methylbenzene (toluene) is a typical example of a nitration that works well with nitric acid in a 1:2 ratio with sulfuric acid. The nitration product is a mixture of 2-, 3- and 4-nitromethylbenzenes:

    Cowardly. 22.4: Electrophilic aromatic substitution (8)

    The presence of significant amounts of water in the reaction mixture is detrimental as water tends to reverse the reaction and generate the nitronium ion:

    \[\ce{NO_2^+} + \ce{H_2O} \translated{\ce{HSO_4^-}}{\rightleftharpoons} \ce{HNO_3} + \ce{H_2SO_4}\]

    For this reason, the strength of a mixture of nitric and sulfuric acids can be significantly increased by using fuming nitric and fuming sulfuric acids. Nitration of relatively unreactive compounds can be achieved with such mixtures. For example, 4-nitromethylbenzene is much less reactive than methylbenzene, but can be converted sequentially to 2,4-dinitromethylbenzene and 2,4,6-trinitromethylbenzene (TNT) on heating with excess nitric acid in fuming sulfuric acid:

    Cowardly. 22.4: Electrophilic aromatic substitution (9)

    The nitration reactions discussed so far have several interesting features. For example, the conditions required for the nitration of 4-nitromethylbenzene would rapidly oxidize the alkene by cleavage of the double bond:

    Cowardly. 22.4: Electrophilic aromatic substitution (10)

    The mononitration of methylbenzene does not lead to equal amounts of the three possible products either. The methyl substituent appears to orient the introduced substituent preferentially at the 2- and 4-positions. This aspect of aromatic substitution is discussed in§ 22-5combined with the effect of substituents on the reactivity of aromatic compounds.

    Some compounds are reactive enough to be nitrated with nitric acid in acetic acid. Suitable examples are 1,3,5-trimethylbenzene and naphthalene:

    Cowardly. 22.4: Electrophilic aromatic substitution (11)

    Other suitable nitrating agents are benzoyl nitrate, \(\ce{C_6H_5COONO_2}\) and ethanoyl nitrate, \(\ce{CH_3COONO_2}\). These reagents are the source of \(\ce{NO_2^+}\) and have some advantages over mixtures of \(\ce{HNO_3} \cdot \ce{H_2SO_4}\) because they are soluble in organic solvents such as ethanonitrile or nitromethane. Homogeneous solutions are particularly important in studies of nitration kinetics. The reactants are usually prepared in solution from the appropriate acyl chloride and silver nitrate, or acid anhydride and nitric acid, as appropriate. Such reagents are hazardous materials and should be handled with care.

    Cowardly. 22.4: Electrophilic aromatic substitution (12)

    Nitrogen salts of the \(\ce{NO_2^+} \ce{X^-}\) type are very strong nitrating agents. The counterion \(\ce{X^-}\) need not be nucleophilic and is typically a fluoroborate, \(\ce{BF_4^-}\) or \(\ce{SbF_4^-}\):

    Cowardly. 22.4: Electrophilic aromatic substitution (13)


    We have simplified electrophilic substitution to some extent by neglecting the possible role of the 1:1 charge-transfer complexes that form most electrophiles with arenes (see Fig.Section 10-3Cto discuss analogous complexes of alkenes):

    Cowardly. 22.4: Electrophilic aromatic substitution (14)

    In the case of halogens, especially iodine, the complexation can be visually recognized by the color of the halogen solutions in the arenes. Although complex formation can aid substitution by bringing the halogen and arenium closer together, substitution does not necessarily occur. A catalyst is usually required and the most common catalysts are metal halides that can accept electrons (i.e. Lewis acids such as \(\ce{FeBr_3}\), \(\ce{AlCl_3}\) and \(\ce{ZnCl_2 } \)). Their catalytic activity can be attributed to their ability to polarize the halogen-halogen bond as follows:

    \[\overset{\delta \oplus}{\ce{Br}} \cdots \overset{\delta \ominus}{\ce{Br}} \cdots \ce{FeBr_3}\]

    The positive end of the dipole attacks the aromatic compound while the negative end becomes complexed with the catalyst. We can represent the reaction sequence as follows, where the slow step is the formation of the \(\sigma\) bond between \(\ce{Br}^\oplus\) and the aromatic ring:

    Cowardly. 22.4: Electrophilic aromatic substitution (15)

    The order of halogen reactivity is: \(\ce{F_2} > \ce{Cl_2} > \ce{Br_2} > \ce{I_2}\). Fluorine is too reactive to be used practically to prepare aromatic fluorine compounds and indirect methods are required (see§ 23-10B). Iodine is usually non-reactive. The iodination has been shown to fail as the reaction is reversed due to the reducing properties of the resulting hydrogen iodide:

    \[\ce{C_6H_6} + \ce{I_2} \overset{\rightarrow}{\longleftarrow} \ce{C_6H_5I} + \ce{HI}\]

    This view is incorrect since, as Kekule himself has shown, iodobenzene is not reduced by hydroiodic acid except at relatively high temperatures.

    One way to achieve direct iodination in the absence of strongly activating substituents is to convert molecular iodine into a more active compound (perhaps \(\ce{H_2OI}^\oplus\) or \(\ce{I}^\oplus\ ).) with an oxidizing agent such as nitric acid or hydrogen peroxide:

    \[\begin{align} \ce{I_2} + 4 \ce{HNO_3} &\rightarrow 2 \ce{H_2O-I^+} + 2 \ce{NO_2} + 2 \ce{NO_3^-} \\ \ce{I_2} + \ce{H_2O_2} + 2 \ce{H^+} &\højrepil 2 \ce{H_2OI^+} \end{align}\]

    Good yields of iodination products are obtained with such combinations:

    Cowardly. 22.4: Electrophilic aromatic substitution (16)

    Halogen substitution reactions with chlorine or bromine must be carried out with adequate protection from strong light. If such precautions are not taken, aAlkylBenzene reacts rapidly with halogen in a photochemical process, replacing the hydrogen in the alkyl group and not the aromatic ring. The reaction features a light-induced radical chain mechanism as discussed for the chlorination of propene (§ 14-3A). Thus, methylbenzene reacts with bromine on illumination to form phenylmethyl bromide; However, when light is excluded and a Lewis acid catalyst is present, substitution occurs, leading primarily to 2- and 4-bromomethylbenzenes. Significantly less 3-bromomethylbenzene is formed:

    Cowardly. 22.4: Electrophilic aromatic substitution (17)

    Benzene itself can be calledadd to Halogens under strong irradiation to polyhalocyclohexanes (see§§ 21-3AI22-9C):


    An important method for the synthesis of alkylbenzenes uses an alkyl halide as the alkylating agent and a metal halide, usually aluminum chloride, as the catalyst:

    Cowardly. 22.4: Electrophilic aromatic substitution (18)

    This reaction class is calledFriedel-Crafts Alkylierungin honor of its discoverers C. Friedel (French chemist) and J. M. Crafts (American chemist). The metal halide catalyst works in the same way as halogenation reactions, providing a source of a positive substituent, in this case a carbonic acid:

    Cowardly. 22.4: Electrophilic aromatic substitution (19)

    The alkylation is not limited to alkyl halides; Alcohols and alkenes can advantageously be reacted in the presence of acidic catalysts such as \(\ce{H_3PO_4}\), \(\ce{H_2SO_4}\), \(\ce{HF}\), \(\ce {BF_3} \) or \(\ce{HF-BF_3}\). Ethylbenzene is produced commercially from benzene and ethene using phosphoric acid as a catalyst. Isopropylbenzene is made from benzene and propene in the same way:

    Cowardly. 22.4: Electrophilic aromatic substitution (20)

    Under these conditions, the carbocation, which is the active substitution agent, is formed by protonation of the alkene:

    \[\begin{align} \ce{CH_2=CH_2} + \ce{H^+} &\rightleftharpoons \ce{CH_3CH_2^+} \\ \ce{CH_3CH=CH_2} + \ce{H^+} & \rightleftharpoons \ce{CH_3} \overset{+}{\ce{C}} \ce{HCH_3} \end{align}\]

    For alcohols, an electrophile can be formed into a carbocation by initial protonation of an acid catalyst and subsequent cleavage:

    Cowardly. 22.4: Electrophilic aromatic substitution (21)

    Limitations of the Alkylation Reaction


    There are several factors that limit the usefulness of the alkylation reaction. First, it can be difficult to restrict the reaction to monosubstitution since the introduction of an alkyl substituent tends to activate the ring for further substitution (see§ 22-5). Therefore, to obtain reasonable yields of monoalkylbenzene, it is usually necessary to use a large excess of the alkylating agent:

    Cowardly. 22.4: Electrophilic aromatic substitution (22)

    Rearrangement of the alkylating agent

    Another limitation is the tendency of the alkylating agent to generate rearrangement products. For example, the alkylation of benzene with 1-chloropropane results in a mixture of propylbenzene and isopropylbenzene. We can write the first reaction to form the propyl cation, which is aBasicCarbonic acid:

    \[\ce{CH_3CH_2CH_2Cl} + \ce{AlCl_3} \rightarrow \ce{CH_3CH_2CH_2^+} + \overset{-}{\ce{Al}} \ce{Cl_4}\]

    This ion can either alkylate benzene to propylbenzene,

    \[\ce{C_6H_6} + \ce{CH_3CH_2CH_2^+} \rightarrow \ce{C_6H_5CH_2CH_2CH_3} + \ce{H^+}\]

    Or it can transform into a more stable secondary ion by transferring hydrogen from an adjacent carbon along with a bonding pair of electrons (i.e., a 1,2-hydride shift). The positive charge is thus transferred from \(\ce{C_1}\) to \(\ce{C_2}\):

    Cowardly. 22.4: Electrophilic aromatic substitution (23)

    Alkylation of benzene with the isopropyl cation then gives isopropylbenzene:

    \[\ce{C_6H_6} + \ce{CH_3} \overset{\oplus}{\ce{C}} \ce{HCH_3} \rightarrow \ce{C_6H_5CH(CH_3)_2} + \ce{H}^\ nadmiar\]

    Rearrangements of this type with intermediate carbocations frequently occur in Friedel-Crafts alkylations with primary and secondary alkyl groups larger than \(\ce{C_2}\) and \(\ce{C_3}\). Related carbocation rearrangements are discussed in§§ 8-9BI15-5E.

    product realignment

    Additional complications arise from the fact that alkylation reactions are sometimes subject to equilibrium control rather than kinetic control. The products often isomerize and are present in disproportionate proportions, especially in the presence of large amounts of catalyst. Thus, 1,2- and 1,4-dimethylbenzenes (kitchen garden- IAgain-xylenes) are converted to 1,3-dimethylbenzene by large amounts of Friedel-Crafts catalysts (Meta-ksylen):

    Cowardly. 22.4: Electrophilic aromatic substitution (24)

    Ethylbenzene disproportionates to benzene and 1,3-diethylbenzene under the influence of excess \(\ce{HF-BF_3}\):

    Cowardly. 22.4: Electrophilic aromatic substitution (25)


    Acylation and alkylation of arenes are closely related. Both reactions date back to a collaboration between Friedel and Crafts in 1877. The acylation reaction introduces an acyl group \(\ce{RCO}\) into the aromatic ring and the product is an aryl ketone:

    Cowardly. 22.4: Electrophilic aromatic substitution (26)

    Frequently used acylating reagents are carboxylic acid halides (\ce{RCOCl}\), anhydrides (\(\ce{(RCO)_2O}\) or the acid itself (\(\ce{RCO_2H}\). A strong proton or another Lewis acid is required The catalyst generates an acyl cation:

    Cowardly. 22.4: Electrophilic aromatic substitution (27)

    The most commonly used catalyst with halides and acyl anhydrides is aluminum chloride:

    Cowardly. 22.4: Electrophilic aromatic substitution (28)

    Acylation differs from alkylation in that the reaction is usually carried out in a solvent, usually carbon disulfide, \(\ce{CS_2}\) or nitrobenzene. Acylation also requires more catalyst than alkylation, since much of the catalyst is bound and deactivated by complexation with the keto product:

    Cowardly. 22.4: Electrophilic aromatic substitution (29)

    In contrast to alkylation, acylation can be easily engineered to achieve a single substitution since it is not possible to introduce another acyl group into the same ring once an acyl group is attached to a benzene ring. For this reason, a convenient synthesis of alkylbenzenes begins with acylation, followed by reduction of the carbonyl group with zinc and hydrochloric acid (§ 16-6). For example, propylbenzene is best prepared by this two-step route because, as we have seen, the direct alkylation of benzene with propyl chloride yields significant amounts of isopropylbenzene and polysubstitution products:

    Cowardly. 22.4: Electrophilic aromatic substitution (30)

    The product is almost always formed in the acylation of alkylbenzeneAgainIsomer. Synthese (4-tertThis is illustrated by -butylphenyl)ethanone and the sequential application of the alkylation and acylation reactions:

    Cowardly. 22.4: Electrophilic aromatic substitution (31)

    Chemists tend to give reactions names that associate them either with their discoverers or with the products they make. This practice can be confusing, as many named responses (or "name responses") that were once thought to be entirely unrelated have been shown to have very similar mechanisms. So we have two closely related acylation reactions: one is the Friedel-Crafts ketone synthesis, where the electrophile \(\ce{R} \ce{-} \overset{\oplus}{\ce{C}} \ce { = O } \); and the other isGattermann-Koch aldehyde synthesiswhere the electrophile is \(\ce{H} \ce{-} \overset{\oplus}{\ce{C}} \ce{=O}\):

    Cowardly. 22.4: Electrophilic aromatic substitution (32)

    The latter reaction uses carbon monoxide and \(\ce{HCl}\) under pressure in the presence of aluminum chloride. One can assume that an electrophile is formed as follows:

    \[\ce{C=O} + \ce{HCl} + \ce{AlCl_3} \rightleftharpoons \ce{H} \ce{-} \overset{\oplus}{\ce{C}} \ce{= O} + \overset{\ominus}{\ce{Al}} \ce{Cl_4}\]


    Substitution of the hydrogen atom in an aromatic hydrocarbon by the sulfonic acid group \(\left( \ce{-SO_3H} \right)\) can be achieved by heating the hydrocarbon with a small excess of concentrated or fuming sulfuric acid:

    Cowardly. 22.4: Electrophilic aromatic substitution (33)

    The actual sulfonating agent is usually the molecule \(\ce{SO_3}\), which is inert but has a strongly electrophilic sulfur atom:

    Cowardly. 22.4: Electrophilic aromatic substitution (34)

    The sulfonation is reversible and the \(\ce{-SO_3H}\) group can be removed by hydrolysis in \(180^\text{o}\):

    Cowardly. 22.4: Electrophilic aromatic substitution (35)

    A sensible alternative production of sulfonyl derivatives is possible with chlorosulfonic acid:

    Cowardly. 22.4: Electrophilic aromatic substitution (36)

    This method has the advantage over direct sulfonation that the sulfonyl chlorides are usually soluble in organic solvents and can be easily separated from the reaction mixture. Sulfonyl chloride is also a more useful intermediate than sulfonic acid, but can be converted to the acid by hydrolysis if necessary:

    Cowardly. 22.4: Electrophilic aromatic substitution (37)

    Sulfonation is important in the commercial manufacture of an important class of detergents, the sodium alkylbenzene sulfonates:

    Cowardly. 22.4: Electrophilic aromatic substitution (38)

    The synthesis illustrates several important types of reactions that we have discussed in this and previous chapters. First, the alkyl group \(\ce{R}\) is usually \(\ce{C_{12}}\) and is derived from the straight-chain hydrocarbon dodecane, which upon photochlorination yields a mixture of chlorododecanes:

    Cowardly. 22.4: Electrophilic aromatic substitution (39)

    This mixture of chlorododecanes is used to alkylate benzene to produce a mixture of isomeric dodecylbenzenesdetergent alkyl:

    Cowardly. 22.4: Electrophilic aromatic substitution (40)

    Sulfonation of a detergent alkylate gives only 4-dodecylbenzene sulfonic acids, which with sodium hydroxide form water-soluble dodecylbenzene sulfonates:

    Cowardly. 22.4: Electrophilic aromatic substitution (41)

    Such cleaning agents, which contain highly branched alkyl groups, are prohibited by law in many countries. This is because quaternary carbon and, to a lesser extent, tertiary carbon are not easily broken down by bacteria in sewage treatment plants:

    Cowardly. 22.4: Electrophilic aromatic substitution (42)

    hydrogen exchange

    It is possible to replace hydrogen atoms in the ring of many aromatic compounds by exchange with strong acids. If an isotopically labeled acid such as \(\ce{D_2SO_4}\) is used, this reaction is an easy way to introduce deuterium. The mechanism is analogous to other electrophilic substitutions:

    Cowardly. 22.4: Electrophilic aromatic substitution (43)

    Perdeuteriobenzene \(^3\) can be produced from benzene in good yields when a sufficiently large excess of deuterosulfuric acid is used. Deuteration appears to be competitive with sulfonation, but in fact deuteration takes place under much milder conditions.

    Aromatic substitution by electrophilic metalation

    Because metals are electropositive elements, they can be considered as potential electrophiles. Their reactions with arenes for mercury have been studied in more detail. Benzene can be replaced by \(\ce{HgX}^\oplus\), a mercury salt derivative, \(\ce{HgX_2}\), in the presence of an acid catalyst. The most commonly used salt is mercury ethoxide, \(\ce{Hg(OOCCH_3)_2}\). The catalyst is believed to act by promoting the production of the active electrophile \(\ce{HgX}^\oplus\). Other metals that can be introduced directly into the aromatic ring in this way are thallium and lead.

    Cowardly. 22.4: Electrophilic aromatic substitution (44)

    \(^3\) prefixTo, as in perdeuterio- or perfluor-, it meansatThe hydrogen atoms were replaced by the mentioned substituent \(\ce{D}\) or \(\ce{F}\). Perhydro means saturated or fully hydrogenated.

    Contributors and Attributions

    John D. RobertIMarjorie C. A small village(1977)Fundamentals of Organic Chemistry, 2nd Edition.WA Benjamin, Inc., Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted according to the following terms: "Permission is granted for the personal, educational, scholarly, and non-commercial reproduction, distribution, display, and performance of this work in any format."


    What are the conditions for electrophilic aromatic substitution? ›

    There are three fundamental components to an electrophilic aromatic substitution mechanism: formation of the new σ bond from a C=C in the arene nucleophile. removal of the proton by breaking the C-H σ bond. reforming the C=C to restore the aromaticity.

    Which is least reactive in electrophilic aromatic substitution? ›

    Benzenesulphonic acid is least reactive in an electrophilic aromatic substitution due to −M effect.

    What are the 2 general steps of electrophilic aromatic substitution? ›

    Electrophilic aromatic substitution has two steps (attack of electrophile, and deprotonation) which each have their own transition state.

    What is an example of electrophilic aromatic substitution reaction? ›

    Nitration and sulfonation of benzene are two examples of electrophilic aromatic substitution. The nitronium ion (NO2+) and sulfur trioxide (SO3) are the electrophiles and individually react with benzene to give nitrobenzene and benzenesulfonic acid respectively.

    What does electrophilic aromatic substitution depend on? ›

    Explanation: The rate of electrophilic substitution depends on the nature of the substituent already present in the benzene ring. If the substituent is o/p directing(activating groups) then the rate of substitution increases. If it is meta directing(deactivating groups) then the rate of substitution decreases.

    What are the factors affecting electrophilic substitution reactions? ›

    Reactivity of electrophilic substitution reactions

    Among the factors that influence reactivity of aliphatic substitution reactions, the nature of substrate, nature of leaving group and solvent characteristics are the most important factors.

    How to determine reactivity of electrophilic aromatic substitution? ›

    Hence, the correct order of reactivity towards electrophilic substitution is: C6H5−OH>C6H6>C6H5−Cl>C6H5−COOH. Q.

    Which of the following is most reactive in electrophilic aromatic substitution? ›

    In series of activating group OH comes first then OCH3, hence, phenol is most reactive towards electrophilic substitution reaction.

    How many types of electrophilic aromatic substitution are there? ›

    There are six key electrophilic aromatic substitution reactions in most introductory organic chemistry courses: chlorination, bromination, nitration, sulfonation, Friedel-Crafts alkylation, and Friedel-Crafts acylation.

    Which compound is more susceptible to electrophilic aromatic substitution? ›

    Hence, aniline is the most reactive towards electrophilic aromatic substitution.

    What is the order of electrophilic substitution? ›

    General order of reactivity towards electrophilic substitution reaction: Aniline > Phenol > Anisole > Acetanilide > Toluene > Chlorobenzene > Fluorobenzene > Benzoic acid > Benzaldehyde > Nitrobenzene.

    What is the difference between electrophilic substitution and electrophilic aromatic substitution? ›

    Electrophilic Aromatic Substitution is the reaction in which an electrophile substitutes hydrogen in the aromatic ring. In contrast, Nucleophilic Aromatic Substitution is the reaction in which a nucleophile substitutes a leaving group in the aromatic ring.

    In which of the following case the rate of electrophilic aromatic substitution will be fastest? ›

    Therefore, C6H5CH3 undergoes electrophilic substitution reaction most easily.

    What are the two examples of electrophilic substitution reaction in benzene? ›

    Basic examples of electrophilic substitution reaction of benzene are nitration, sulfonation, halogenation, Friedel Craft's alkylation and acylation, etc.

    What is the main problem encountered during electrophilic substitution? ›

    The main problem encountered during electrophilic substitution reactions of aromatic amines is that of their very high reactivity.

    Which compound gives electrophilic substitution with most difficulty? ›

    −NO2 group is highly deactivating and thus, deactivates the ring towards electrophilic substitution. Hence, sulphonation of nitrobenzene is most difficult.

    What determines electrophilic strength? ›

    greater degree of positive charge increases electrophilicity, so a carbocation is more electrophilic than a carbonyl carbon. Additionally, the nature of the leaving group influences electrophilicity in species without empty orbitals; better leaving groups make it more likely that a reaction will happen.

    Which is the most reactive species towards electrophilic addition reaction? ›

    Therefore, o-hydroxy toluene is most reactive towards electrophilic reagent.

    What are the three necessary conditions for any system to be aromatic? ›

    The necessary conditions for any system to be aromatic are planar, conjugated ring system with delocalisation of (4n+2)π electrons, where, n is an integer. Was this answer helpful?

    What are the conditions for electrophilic substitution of benzene? ›

    The electrophilic substitution reaction between benzene and chlorine or bromine. Benzene reacts with chlorine or bromine in an electrophilic substitution reaction, but only in the presence of a catalyst. The catalyst is either aluminum chloride (or aluminum bromide if you are reacting benzene with bromine) or iron.

    What are the conditions for a good electrophile? ›

    There are two requirements for a molecule to be considered a good electrophile. First, it must contain an electrophilic center or atom. Second, the electrophilic atom must be able to accommodate a new sigma bond.

    What are two conditions for aromaticity? ›

    A compound is said to be aromatic if it satisfies the following three conditions: (i) It should have a planar structure. (ii) The n-electron of the compound are completely delocalized in the ring. (iii) The total number of π–electrons present in the ring should be equal to (4n + 2), where n = 0, 1, 2 … etc.


    Top Articles
    Latest Posts
    Article information

    Author: Tyson Zemlak

    Last Updated: 10/10/2023

    Views: 5645

    Rating: 4.2 / 5 (63 voted)

    Reviews: 94% of readers found this page helpful

    Author information

    Name: Tyson Zemlak

    Birthday: 1992-03-17

    Address: Apt. 662 96191 Quigley Dam, Kubview, MA 42013

    Phone: +441678032891

    Job: Community-Services Orchestrator

    Hobby: Coffee roasting, Calligraphy, Metalworking, Fashion, Vehicle restoration, Shopping, Photography

    Introduction: My name is Tyson Zemlak, I am a excited, light, sparkling, super, open, fair, magnificent person who loves writing and wants to share my knowledge and understanding with you.