Nitration the replacement of a hydrogen atom in the ring by a nitro no2 group is called nitration. Electrophilic aromatic substitution reactions are characteristic of aromatic compounds, and are important ways of introducing functional groups of benzene rings. Because of the delocalised electrons exposed above and below the plane of the rest of the molecule, benzene is obviously going to be highly attractive to electrophiles species which seek after electron rich areas in other molecules. We substituted this hydrogen right here with this electrophile, or what was previously an electrophile, but then once it got an electron, its just kind of a group that is now on the benzene ring. Order of electrophilic substitution chemistry stack exchange.
Electrophilic substitution reactions are chemical reactions in which an electrophile displaces a functional group in a compound, which is typically, but not always, a hydrogen atom. General mechanism of electrophilic aromatic substitution, halogenation, nitration, sulfonation. Electrophilic aromatic substitution of benzene with mechanism and. Discuss the mechanism of electrophilic substitution.
A mechanism for electrophilic substitution reactions of benzene. Electrophilic substitution the general equation for this reaction is. Benzene ring serves as a source of electrons nucleophile due to the presence of electron cloud. Nucleophilic substitution and elimination walden inversion ooh oh ho o s malic acid ad 2. Electrondonating groups stabilize the carbocation intermediate of electrophilic aromatic substitution. The mechanism for electrophilic substitution of benzene. Theyll give your presentations a professional, memorable appearance the kind of sophisticated look that todays audiences expect. An electrophilic aromatic substitution consists of three main fundamental components. Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system usually hydrogen is replaced by an electrophile. Keep in mind that the mechanisms of electrophilic aromatic substitution reactions are all very.
Electrophilic aromatic substitution of benzene with. So we start with the benzene ring, and we react benzene with a molecule that contains an electrophile in there. All three double bonds are retained in the product. Follow these instructions to unlock the download links. In the first, slow or ratedetermining, step the electrophile forms a sigmabond to the benzene ring, generating a positively charged benzenonium intermediate. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature. The indole ring is highly reactive at its 3position toward protonation, halogenation, alkylation and acylation.
Partial rate factors relative rate of electrophilic aromatic substitution compared to benzene electron rich aromatic rings are more nucleophlic. The electrophilic substitution reaction between benzene and nitric acid. The strongly activating hydroxyl oh and amino nh 2 substituents favor dihalogenation in examples 5 and six. Worlds best powerpoint templates crystalgraphics offers more powerpoint templates than anyone else in the world, with over 4 million to choose from. Electrophilic substitution reactionncert hydrocarbons. Substitution reactions of compounds having an antagonistic orientation of substituents require a more careful analysis. Benzene is aromatic a cyclic conjugated compound with 6. In an electrophilic aromatic substitution reaction, a hydrogen atom is replaced by. Benzene reacts with an electrophile using two of its. Write a stepwise mechanism for the nitration of benzene.
Feb 15, 2014 electrophillic substitution of benzene 1. Electrophilic substitution reactions of benzene definition. Electrophilic substitution an overview sciencedirect topics. Electrophilic aromatic substitution of benzene with mechanism. Substitution reactions in aromatic compounds nptel. If a substituted benzene undergoes further substitution mostly.
Mar 12, 2014 my previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. It is carried out by heating benzene with the nitrating mixture consistin. Winner of the standing ovation award for best powerpoint templates from presentations magazine. Ppt electrophilic aromatic substitution powerpoint. Benzene electrophilic aromatic substitution free download as powerpoint presentation. The benzene ring is stable and does not break under normal chemical conditions. Jul 05, 2017 the main difference between nucleophilic and electrophilic substitution reaction is that the nucleophilic substitution reaction involves the displacement of a leaving group by a nucleophile whereas the electrophilic substitution reaction involves the displacement of a functional group by an electrophile. Benzene reacts with hot concentrated nitric acid and sulfuric acid to yield nitrobenzene. But this is the electrophilic aromatic substitution. Because, of course, the benzene ring is electron rich even though the bonds are a bit stronger, you tend to only really see these types of reactions unless you have somehow activated your benzene ring with electron withdrawing groups. A twostep mechanism has been proposed for these electrophilic substitution reactions.
Lets look at the general reaction for electrophilic aromatic substitution. Benzene and other arenes are electron rich molecules. The mechanism of electrophilic aromatic substitution follows two elementary steps. The mechanism for the substitution of an alkyl group such as ch 3 ch 2 into benzene, by a reaction involving an alkene such as ethene. Typical reactions of benzene ring namely halogenation, nitration, sulphonation, and friedelcraft reaction are electrophilic substitutions. Electron withdrawing groups deactivate the benzene ring to electrophilic aromatic substitution. The mechanism for the substitution of an alkyl group such as ch 3 into benzene. Such a reaction is not favorable, thermodynamically. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at a temperature not exceeding 50c. Nitration is the usual way that nitro groups are introduced into aromatic rings. Using the drawing window on the left below, draw the major product from each of the electrophilic aromatic substitution reactions shown below.
Electrophilic aromatic substitution mechanism video khan. The other main type of electrophilic substitution reaction is an electrophilic aliphatic substitution reaction. Nitration is a typical example of an aromatic electrophilic substitution reaction in which the nitronium ion n o 2 0 acts an electrophile. Therefore benzene reacts via substitution swapping which retains the ring, rather than addition, which would. And what happens in electrophilic aromatic substitution. A substitution reaction is a reaction that involves the replacement of an atom or a group of atoms by another atom or a group of atoms. Chemistry of benzene electrophilic aromatic substitution based on mcmurrys organic chemistry, 7th edition 2 substitution reactions of benzene and its derivatives.
Organic chemistry ii chem 252 chapter 15 reactions of. Electrophilic aromatic substitution 3 a general mechanism for electrophilic aromatic substitution. Electrophilic substitution is the typical reaction type for. It is carried out by heating benzene with the nitrating mixture consisting of concentrated nitric acid and sulphuric acid to about 330k. Electrophilic substitution of disubstituted benzene rings. Benzene will react with hot concentrated nitric acid to produce nitrobenzene.
Electrophilic substitution an overview sciencedirect. Electrophilic aromatic substitution video khan academy. In this reaction the electrophile is nitronium ion. Benzene electrophilic aromatic substitution aromaticity.
Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalystfree bromination of benzene to give bromobenzene and hbr. Aromaticity and electrophilic aromatic substitution. Main difference nucleophilic vs electrophilic substitution reaction. Were going to substitute the electrophile for a proton on our benzene ring. Note that in this reaction and in others that follow, only one of the six benzene hydrogens is shown explicitly to emphasize that one hydrogen is lost in the reaction. Electrophilic attack on mono substituted benzene derivatives when considering the possible products of an electrophilic aromatic substitution reaction of a mono substituted benzene derivative, the incoming electrophile may be incorporated at the ortho, meta or paraposition. Electrophilic aromatic substitution mechanism video. Principles and mechanisms 2nd edition by joel karty in pdf from following download links. However, this reaction proceeds slowly, which is inconvenient. Mar 30, 2017 the benzene ring is stable and does not break under normal chemical conditions. Due to the presence of lewis acid, generation of electrophile takes place. Second, removal of a proton from that cation restores aromaticity. My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. A sulfonic acid group, so 3 h, can also be introduced onto an aromatic ring by electrophilic aromatic substitution.
Electrophilic substitution reactions of indoles request pdf. In an electrophilic aromatic substitution reaction, a hydrogen atom is replaced by an electrophile. Electrophilic substitution of benzothiazole occurs on the fused benzene ring, essentially at the 4 and 6 positions. The benzene ring is stable is requires a lot of energy to break and stay broken. Apr 20, 2015 the benzene ring is stable is requires a lot of energy to break and stay broken. As the lewis acid accepts the electron pair from the attacking reagent. The net reaction for nitration of benzene is the result of electrophilic attack by the nitronium ion on the aromatic ring followed by loss of a proton. King chapter 18 electrophilic aromatic substitution i. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Electrophilic aromatic substitution mechanism and reaction. The reaction passes through an intermediate which is variously called. This is the general default model for this particular reaction and this is one of the most common ones.
These substitution reactions are very important in the synthesis of certain compounds. Substitution reactions of benzene and its derivatives benzene is aromatic. Sometimes download links isare not visible on mobile devices, so if you face this issue, kindly do visit this page via laptopdesktop computer. The electrophilic reagent will attack the aromatic nucleus and the hydrogen atom of benzene is displaced by the electrophilic reagent. With an appropriate catalyst, benzene will react with bromine.
Electrophilic aromatic substitution the most characteristic reaction of aromatic compounds is electrophilic aromatic substitution, in which one of the ring hydrogens is substituted by a halogen, nitro group, sulfonic acid group, alkyl or acyl group. It can be attacked by electrophiles which will swap with the hydrogens. Compared to benzene, such substituents result in a higher reaction rate of a second electrophilic aromatic substitution. Both nucleophilic and electrophilic substitution reactions are found in organic and inorganic chemistry. The orientation and mechanism of electrophilic aromatic. Electrophillic substitution of benzene linkedin slideshare. Dec 07, 2015 electrophilic substitution reaction ncert hydrocarbons 1.
In this respect benzene resembles an alkene, for in the reaction of an alkene with an electrophilic the site of attack is the exposed bond. Aromatic structure an overview sciencedirect topics. Electrophilic aromatic substitution reactions bromination. Aromatic compounds react through a unique substitution type reaction. Step 3 loss of a proton from the carbocation to give a new aromatic compound. Electrophilic substitution reactions involving positive ions.
The topic of this chapter is electrophilic substitution of indole and its derivatives. Scribd is the worlds largest social reading and publishing site. Notice that either of the oxygens can accept the electron pair. Electrophilic substitution reactions of benzene flashcards. Benzene is susceptible to electrophilic attack primarily because of its exposed electrons. As temperature increases there is a greater chance of getting more than one nitro group, no 2, substituted onto the ring. The major products of electrophilic substitution, as shown, are the sum of the individual group effects. An electrophilic substitution reaction generally involves three steps.
1262 575 690 815 240 772 485 289 489 227 899 714 229 1379 1408 1293 1029 834 910 798 625 546 459 1374 779 794 1114 1208 1174