This tutorial extends the discussion of electrophilic aromatic substitution reactions to polysubstituted benzene rings. Limitations of electrophilic aromatic substitution. Acylation of benzene 3d video animation education youtube. Electrophilic aromatic substitution reactions are characteristic of aromatic compounds, and are important ways of introducing functional groups of benzene rings. Ring deactivators decrease the electron density on the benzene ring, thus making the ring less reactive toward electrophilic aromatic substitution reactions. 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. While this is similar to alkene reactions at first glance the remainder of this mechanism is very different and unique. Professor davis walks through a simple electrophilic substitution of benzene. Electrophillic substitution of benzene linkedin slideshare. The mechanism for the substitution of atoms like chlorine and bromine into benzene rings. The electrophilic aromatic substitution reaction is the attack of a benzene ring on an electrophilic species resulting in the substitution of a proton with a functional group.
Join now to read essay nitrating acetanilide and methyl benzoate. Additionally, the low reactivity of benzene rings requires that the electrophile be extremely reactive. As an example here is the general pattern for the electrophilic aromatic substitution reactivity of furan, complete with the 3 important resonance structures that justify the reactivity of the 2position. Electrophilic aromatic substitution of benzene youtube. The mechanism of electrophilic aromatic substitution follows two elementary steps. It answers the question where will a reaction take place on the benzene ring if it already contains a substituent. Benzene is a planar molecule having delocalized electrons above and below the plane of ring.
Nucleus equal to atomic nucleus or having positive charge. The electrophilic aromatic substitution reaction starts when one of the pi electrons on the benzene rings breaks as it reaches for the super electrophile. What will be the order of reactivity towards electrophilic substitution in case of the following compounds. So thats where that thats where the electrophilic part comes in this. Benzene and benzene derivatives undergo electrophilic substitution rather than addition to maintain their aromaticity. Substitution reactions of benzene and its derivatives benzene is aromatic. In this video we want to discuss the electrophilic substitution mechanism of benzene using 2 reactions as example. By definition, a molecule which forms a covalent bond by accepting a pair of electrons is called an electrophile. Electrophilic aromatic substitution nitration of benzene. Benzene, c 6 h 6, is a planar molecule containing a ring of six carbon atoms each with a hydrogen atom attached there are delocalised electrons above and below the plane of the ring.
Many other substitution reactions of benzene have been observed. Due to the presence of lewis acid, generation of electrophile takes place. Question 10 which of the following statements regarding electrophilic aromatic substitution is wrong. And so over here, we can see the electrophile is now in place of that proton. This organic chemistry video tutorial provides a basic introduction into the nitration of benzene mechanism which is one of the most common electrophilic aromatic substitution reaction. The delocalized pi electron cloud present in the benzene ring behaves source of electron i. 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. Why substitution not addition university of calgary in. Click the structures and reaction arrows in sequence to view the 3d models and animations respectively. Therefore, it undergoes electrophilic substitution reactions very easily. As the aromaticity of benzene is not disturbed in the reaction, these reactions are highly spontaneous in nature.
As a result, it is highly attractive to electron deficient species i. The real structure is an intermediate of these structures represented by a resonance hybrid. In the nitration of benzene, anhydrous nitric acid reacts with sulphuric acid as a catalyst to form an electrophile which then attacks the benzene and attaches to it. Instead, benzene rings undergo substitution reactions referred to as electrophilic aromatic substitution eq. Electrophilic aromatic substitution video khan academy. Benzene has 2 resonance structures but taken individually none show the delocalisation of electrons and they can exist at the same time as electrons are delocalised. In the sandmeyer reaction and the gattermann reaction diazonium salts react with halides the smiles rearrangement is the intramolecular version of this reaction type. The first reaction is nitration of benzene to nitrobenzene. Explain the reason for the ones that do not work and show the other expected product if any for each reaction. Electrophilic aromatic substitution is when an atom is attached to an aromatic system normally hydrogen,and is superseded by an electrophile. Why does benzene undergo electrophilic substitution.
The 5 membered heterocycles react in a similar way. Friedelcrafts alkylation reaction between tbutenium could be produced from tbutanol and benzene visualized using vmd. Ppt electrophilic aromatic substitution powerpoint. And what happens in electrophilic aromatic substitution.
Electrophilic aromatic substitution mechanism video. Electrophilic aromatic substitution chemistry steps. Nitration of benzene firstly involves the formation of a very powerful electrophile, the nitronium ion, which is linear. Benzene is a strong nucleophile so is able to donate a pair of electrons to an electrophile, forming a dative covalent bond. Electron withdrawing groups deactivate the benzene ring to electrophilic aromatic substitution. Electrophilic aromatic substitution ashley%piekarski,%ph.
Electrophilic aromatic substitution reactions of benzene wolfram. For example, cl 2 will not react with benzene, whereas. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Resonance theory can be used to illustrate these processes. Free interactive 3d chemistry animations and models for advanced school chemistry and undergraduate chemistry education hosted by university of liverpool. Electrophilic aromatic substitution of benzene with. Electrophilic aromatic substitution based on mcmurry\s organic chemistry, 7 th version. In the bamberger rearrangement nphenylhydroxylamines rearrange to 4aminophenols. That is, they control where the new substituent appears in the product. The specific electrophile believed to function in each type of reaction is. For an addition pathway, the nucleophile then adds to the electrophilic carbocation giving a cyclohexadiene derivative for a substitution pathway, the nucleophile functions as a base and removes a proton from the sp 3 c to recreate the cc and restore the aromaticity.
Ring activators are groups that increase the electron density on the benzene ring and thereby make the ring more susceptible to electrophilic aromatic substitution reactions. Electrophilic aromatic substitution chemistry libretexts. The mechanism of electrophilic aromatic substitution and the effect of electron withdrawingdonating substituents. The basics of electrophilic aromatic substitution youtube. Electrophilic aromatic substitution of heteroaromatics.
Chemistry on electrophilic substitution in benzene. Why does benzene undergo only electrophilic substitution. The colours used match the molymod r spheres to allow for the complementary use of 3d models to further aid visualisation and memory. Were going to substitute the electrophile for a proton on our benzene ring. An electrophilic substitution reaction generally involves three steps. Bromination stability of the intermediate in electrophilic aromatic substitution is lesser than that of the starting benzene ring reaction of an electrophile is endergonic, possesses substantial activation energy, and comparatively slow 12. In addition to exerting an effect on the speed of reaction, substituents on the benzene ring also influence the regiochemistry of the reaction. Order of electrophilic substitution chemistry stack exchange.
Why does benzene only undergo electrophilic but not nucleophilic substitution. This demonstration shows a common class of reactions of benzene. Second, removal of a proton from that cation restores aromaticity. Any molecule, ion or atom that is electron deficient in any way can behave as an electrophile. Nitration of benzene mechanism electrophilic aromatic. In electrophilic aromatic substitution reactions, a cyano substituent on the aromatic ring is. In the case of benzene, the hybrid structure is the one below the one you learn at school. Regardless of what electrophile is used, the electrophilic aromatic substitution mechanism can be divided into two main steps. Electrophilic substitution on 2nitrovinylbenzene occurs at the meta position. As the lewis acid accepts the electron pair from the attacking reagent. 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.
This is what you need to understand for the purposes of the electrophilic substitution mechanisms. Some typical substitution reactions on arenes are listed below. Electrophilic nitration of benzene with nitric acid essay. Electrophilic aromatic substitution on the anilinium ion. This animation helps students to visualise the interaction between the two molecules and the movement of electrons and atoms within, traditionally illustrated by curly arrows. Determine which electrophilic aromatic substitution reactions will work as shown. Illustrative reactions ofelectrophilic aromatic substitution. Electrophilic aromatic substitution of benzene with mechanism and. 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. The mechanism for electrophilic substitution of benzene. When aniline is placed in strong acid the nitrogen atom is protonated.
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