That is, they control where the new substituent appears in the product. Abstracs the electrophilic substitution reactions nitration and bromination in benzene and its some monoand dialkylsubstituted derivatives with alkyl groups c1c4 are explored. Electrophilic aromatic substitution reactions an organic reaction in which an electrophile substitutes a hydrogen atom in an aromatic compound. Electrophilic aromatic substitution reactions, course notes archive, 1. Learn electrophilic aromatic substitution with free interactive flashcards. Position of electrophilic attack for disubstituted benzenes 1 where two groups reinforce each other, the outcome is obvious.
Many functional groups can be added to aromatic compounds via electrophilic aromatic substitution reactions. Ppt electrophilic aromatic substitution powerpoint. Mar 14, 2014 eas tutorial video series breaking down electrophilic aromatic substitution from a logical perspective. Choose from 500 different sets of electrophilic aromatic substitution flashcards on quizlet.
A functional group is a substituent that brings with it certain chemical reactions that the aromatic compound itself doesnt display the bromination of benzene. 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. In an electrophilic aromatic substitution reaction, existing substituent groups on the aromatic ring influence the overall reaction rate or have a directing effect on. Recall that the basis for orthopara and meta directing effects is whether the. However, even though they contain unshared electron pairs, they are deactivating toward electrophilic aromatic substitution because of the electronegative effect of the halogens. Sets of substituents are all orthopara directing in electrophilic aromatic substitution reactions. Electrondonating groups stabilize the carbocation intermediate of electrophilic aromatic substitution. Electrophilic aromatic substitution objective the objective of this exercise is to explain the observed effects of orthopara and meta directing substituents of electrophilic aromatic substitution in terms of the partial charge on each aromatic carbon atom. A nucleophilic aromatic 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. Electrophilic aromatic substitution electrophilic aromatic.
In the first step, the addition of an electrophile yields a highenergy carbocation in which the aromatic. Attack of the electrophile on the aromatic ring, creating a resonancestabilized. Pdf electrophilic aromatic substitution as one of the most fundamental chemical. 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. The greater acidity of pyrroles and indoles is a consequence of. In this friedelcrafts acylation, we use the acylium ion for electrophilic attack on the aromatic ring. Substituent directing effect the electrophile attacks the nucleophilic pibond on the benzene ring, but the. It deactivates benzene ring towards electrophilic substitution reaction. The first three examples have two similar directing groups in a metarelationship to each other.
Electrophilic aromatic substitution reactions ucla chemistry. What is the increasing rate of electrophilic substitution. All electronwithdrawing groups are metadirectors, except the halogens. The chloro and bromo groups are orthopara directors. Substituents and electrophilic aromatic substitution eas reaction rates. If you substitute a nitro group, no 2, into the benzene ring in methylbenzene, you could possibly get any of the following products the carbon with the methyl group attached is thought of as the number 1 carbon, and the ring is then numbered around from 1 to 6. However, the aldehyde functional group is a meta directing deactivating group that will promote electrophilic attraction at the only meta positionthe bottom vertexand restrict substitution at the carbon atoms adjacent to it.
All electrophilic aromatic substitution reactions share a common mechanism. Activating groups increase the rate of electrophilic aromatic substitution, relative to hydrogen. Electrophilic aromatic substitution eas is a substitution reaction usually involving the benzene ring. Green iodination of vanillin chem 22l unc charlotte. Since sigma complex formation is the rate determining step of eas reactions, benzene derivatives are divided into two groups based on how the substituent stabilizes or destabilizes the positively charged sigma complex. Electrophilic substitution involves the attack of a electrophile which is deficit of electrons. Such groups are called electron withdrawing groups and are meta directing groups in electrophilic aromatic substitution. The second difference is that the br in the electrophilic aromatic substitution reaction replaces the hydrogen while both hydrogens are still there when they are on the alkene. There are five general types of electrophilic aromatic substitution reactions. While the mechanism undergoes a broken pi bond and addition to the former sp2 carbon atom, the eas reaction is very very different from the alkene addition reactions youve studied back. Thinkbook benzene benzene is best represented as a resonance hybrid. Electrophilic substitution the general equation for this reaction is.
Electrophilic aromatic substitution directing groups master. Back side attack as in sn2 and inversion is precluded by the geometry of the ring 1. Halogenation of benzene with br2, cl2 or i2 occurs through the same mechanism. Herein lies the difference between aromatic substitution and alkene addition. Today well describe the two main patterns by which substituents direct electrophilic aromatic substitution. Nucleophilic aromatic substitution chemistry libretexts. For example, the complete mechanism for substitution into the 4 position is.
Electrophilic aromatic substitution eas an aromatic proton is replaced by an. If the relative yield of the ortho product and that of the. The first difference of benzene being less reactive brings the need for using a lewis acid febr 3 which turns the br 2 into a stronger electrophile and makes the reaction possible. Kinetic products are always more stable than thermodynamic. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, and alkylation and alkylating friedelcrafts reaction. Followed by detailed tutorial videos on the individual aromatic reactions. This is video 11 in the electrophilic aromatic substitution video series.
The reactivity and regioselectivity of this category of reactions is significantly impacted by the group that is already attached to the aromatic ring. Although precise reactivity ratios depend on the particular reaction, the relative rates of bromination are typical. All activating group donate electrons through inductive effects andor resonance. Acidity of pyrrole and indole pyrrole and indole are weak acids.
Chlorine is a meta directing, activating substituent for electrophilic aromatic substitution. Substitution into the 3 position the first step methyl groups direct new groups into the 2 and 4 positions, but a nitro group, no 2, already on the ring directs incoming groups into the 3 position. 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. Electrophilic aromatic substitution chemistry libretexts. In examples 4 through 6, oppositely directing groups have an ortho or pararelationship. Nitric and sulfuric acid react to form the nitronium ion electrophile.
Start by comparing eas to alkene reactions then understand how this differs. The electrophilic nitronium ion reacts with the nucleophilic cc of the arene. The nature of orthopara and meta group directing in electrophilic aromatic substitu tion article pdf available in the journal of chemical physics 14119. Electrophilic aromatic substitution is a multistep process. Electrophilic aromatic substitution video khan academy. The major products of electrophilic substitution, as shown, are the sum of the individual group effects. Substituents already attached to benzene exert an influence on additional atoms or groups attempting to bond to the benzene ring via electrophilic aromatic substitution reactions. Fill in the starting materials and reagents needed to obtain the major product shown via electrophilic aromatic substitution.
Substitution reactions of benzene and its derivatives benzene is aromatic. Sets of substituents are all deactivating groups in electrophilic aromatic substitution reactions. Aromatic nitro compounds are used as explosives, antibiotics, and synthetic intermediates in the production of dyes, foams, analgesics, antidegradants for rubber, and synthetic fibers. Electrophilic aromatic substitution is a typical reaction for bhs. Electrophilic aromatic substitution electrophilic aromatic substitution. Which of the following statements regarding electrophilic aromatic substitution is wrong. An atom or group already attached to a benzene ring may direct an incoming electrophile to either the ortho.
In electrophilic aromatic substitution reactions the nitro group is. Electron withdrawing groups deactivate the benzene ring to electrophilic aromatic substitution. In electrophilic aromatic substitution, the attacking species electrophile necessarily is a lewis acid the electrophilic bromination or chlorination of benzene requires, in addition to the halogen. Why is nitro group a meta directing in electrophilic aromatic substitution reaction ans in nitrobenzene, nitro group no2 is attached to the benzene ring. Oxford university press online resource centre multiple.
If the conditions of the reaction are not too acidic, aniline and its derivatives undergo rapid ring substitution. The mechanism of electrophilic aromatic substitution. Thus, the nitro group is a meta directing group because all electrophilic substitution reactions of nitrobenzene occur at the meta position. In an electrophilic aromatic substitution reaction, a hydrogen atom is replaced. In addition to exerting an effect on the speed of reaction, substituents on the benzene ring also influence the regiochemistry of the reaction. This organic reaction is typical of aromatic compounds and a very u seful method for adding substit uents.
Substituents stabilize positive charge on substituted carbon. King chapter 18 electrophilic aromatic substitution i. Electrophilic aromatic substitution directing groups. In electrophilic aromatic substitution reactions the hydroxyl group is an o,pdirector because. A monosubstituted benzene, when treated with an electrophile, could undergo three electrophilic aromatic substitution reactions. Additionally, the aldehyde group adds steric hindrance to its surrounding environment. Groups promoting substitution at the orthopara and meta position are called orthopara and meta directing. Electrophilic aromatic substitution in polycyclic structures. Aromatic compounds are more stable than antiaromatic compounds.
A substituent group is either an ortho, paradirecting group or a metadirecting group in all electrophilic aromatic substitution reactions. Electrophilic aromatic substitution reactions, course notes archive, 1 disclaimer. In cases of opposing effects prediction is more difficult and mixtures may result. Electrondonating and withdrawing groups on polycyclic structures. Electrophilic aromatic substitution furan, thiophene, and pyrrole, like benzene and naphthalene, undergo electrophilic aromatic. A functional group is a substituent that brings with it certain chemical reactions that the aromatic compound itself doesnt display. The nitronium ion no2 is the reactive electrophile in this reaction. Its application goes way beyond electrophilic aromatic substitution reactions. An electrophilic aromatic substitution is a process where one atom or group on an aromatic ring is replaced by an incoming electrophile. Sn1 leads to phenyl cation which is less stable than a primary carbocation two types of mechanisms that operate in nucleophilic substitutions are, 1. Every one of these groups, therefore, makes the ring more electron rich than benzene and thereby makes the ring more susceptible to attack by electrophiles i. Resonance effect of activating and deactivating groups it is also important to note that when an electrophilic aromatic substitution reaction is performed on a monosubstituted benzene ring containing an activating group, the new electrophile will.
There are 6 nucleophilic substitution mechanisms encountered with aromatic systems. In the mo treatment, some indices such as free valence 40, localization energy 41, and other quantities 42,43 have been introduced to predict the orientation of electrophilic aromatic substitution. For product ratios, the two easiest peaks to use are at 4. Regardless of what electrophile is used, the electrophilic aromatic substitution mechanism can be divided into two main steps. Take a benzene with a group like och3 attached to it. Its one thing to learn about electrophilic aromatic substitution reactions of benzene itself.
A free powerpoint ppt presentation displayed as a flash slide show on id. An electron donating group edg or electron releasing group erg is an atom or functional group that donates some of its. Electrophilic substitution is the typical reaction type for aromatic rings. We study several common electrophiles how each is generated. A nucleophilic aromatic substitution reaction is a reaction in which one of the substituents in an aromatic ring is replaced by a nucleophile a meisenheimer complex is a negatively charged intermediate formed by the attack of a nucleophile upon one of the aromatic ring carbons during the course of a nucleophilic aromatic substitution reaction. The origin of this selectivity will be discussed in the next section.
An electrophilic aromatic halogenation is a type of electrophilic aromatic substitution. Deactivating groups decrease the rate of electrophilic aromatic substitution, relative to hydrogen. This is the rate determining step as it destroys the aromaticity of the arene. Electrophillic substitution of benzene linkedin slideshare. The topic of eas or electrophilic aromatic substitution reactions is one that covers a key reaction pathways studied in the average organic chemistry course. An electrophilic aromatic substitution consists of three main fundamental components. Partial rate factors relative rate of electrophilic aromatic substitution compared to benzene electron rich aromatic rings are more nucleophlic. How does resonance influence the rate of this reaction. The halogens are in a class by themselves, being deactivating but ortho. Directing group effects in electrophilic aromatic substitution aromatic rings containing very strongly activating groups such as oh phenol and nh 2.
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