Identify the substituent as an orthopara or meta director. In ortho substitution, two substituents occupy positions next to each other, which may be numbered 1 and 2. Bromine as the orthodirecting group in the aromatic. Why is benzoic acid a meta directing group answers. The aldehyde carbonyl group and carbonyl groups in general is a metadirecting substituent. And, what if the position you want to put it on is taken up by another group. The first scenario for adding an electrophile to a monosubstituted benzene ring is when the substituent is an electron donating group. Now that youve mastered resonance, lets take a look at the directing effects of activating and deactivating groups. A summary of the directing effects of common substituent groups is given in the third column of table 16. By default the meta product forms faster because it lacks this destablizing resonance structure. Well look at the resonance structures of the intermediate for an explanation. The protodeboronation was successfully applied to the synthesis of ortho and metafunctionalized phenols using the boronic acid moiety as a blocking group and a directing group, respectively.
The nature of orthopara and meta group directing in electrophilic aromatic substitution. Can we extend this analysis to groups which are meta directing. The protodeboronation was successfully applied to the synthesis of ortho and meta functionalized phenols using the boronic acid moiety as a blocking group and a directing group. All meta directors are deactivators, no exceptions.
Two substituents in a 1,2 relationship are said to. This is a part of a detailed tutorial video series. Electron donating groups are alkyl groups, phenyl groups or substituents that have a lone. Pdf electrophilic aromatic substitution as one of the most fundamental chemical processes is affected by atoms or groups already.
The effect of an electron donating groups on a benzene ring. Lets see if we can figure out why by looking at some resonance structures for this mechanism. Thus these positions are deactivated towards electrophilic aromatic substitution. Meta directing groups the meta directing groups in table 16. These groups are referred to as activating groups because they speed up the reaction. Several methods exist in order to separate these isomers.
Groups that have an unshared electron pair on the atom attached to the aromatic ring, such as amino, hydroxyl, alkoxyl, and amides or esters with the oxygen or nitrogen directly. H activation has been known for the last few decades. Orthopara directors i video khan academy free online. Orthopara directors alkyl substituents are electrondonating groups and they are activating groups. H bonds in aromatic molecules remained elusive for a long time.
It discusses the reactivity and directing effects of strong activating groups, moderately. All orthopara directors are activators, except for halides. H activationborylationoxidation protocol for the preparation of phenols is described. Accessing meta functionalized phenols from the parent phenols, on the other hand, generally requires lengthy synthetic sequences. The first metal free thermal protodeboronation of ortho and paraphenol boronic acids in dmso was developed. Here, we report the first methodology for the onepot direct meta selective arylation of phenols. This method is particularly attractive for the generation of metasubstituted phenols bearing orthoparadirecting groups, as such substrates are difficult to access by other phenol syntheses. Both the regioselectivitythe diverse arene substitution patternsand the speed of an electrophilic aromatic substitution are affected by the substituents already attached to the benzene ring. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The term is usually applied to ch activation of hydrocarbons, where it is defined as a coordinating moiety an internal ligand, which directs a metal catalyst into the proximity of a certain ch bond. But once you move beyond benzene, thats when things start getting really interesting today well describe the two main patterns by which substituents direct electrophilic aromatic substitution. So in our first example here well do an ortho attack where we add the nitro. Nitration of arenes bearing orthopara directing groups. Meta directorsusually groups that withdraw electron density from the ring.
Type 2 all groups having their key atom multiply bonded to more powerful element are meta dir. Inductive effects of alkyl groups chemistry libretexts. Protodeboronation of ortho and paraphenol boronic acids. Alkyl group, benzene ring, oh, or, nh2, nhr, nr2, f, cl, br, i ortho attack. For example, x, o, oh, or, ocor, nh2, nhr, nhcor etc. An electrophilic aromatic substitution is a process where one atom or group on an aromatic ring is replaced by an incoming electrophile. Dont worry, 16 minutes or so from now it will all make sense. Ortho effect definition, explanation, ortho effect in. Any activating group directs the electrophile to the ortho and. We know that 2 large groups will have to face steric hindrance while coming into proximity. Note that if two different sites are favored, substitution will usually occur at the one that is least hindered by ortho groups.
Meta directors i video directing effects khan academy. Electrophilic aromatic substitution mechanisms and reactions. Working on the concept of democratisation of education. Discuss doubts with iit jee aspirants on our online jee prep portal like vineet khatri sir on facebook. Hence substitution occurs preferentially on those sites. The nature of orthopara and meta group directing in electrophilic aromatic substitution article pdf available in the journal of chemical physics 14119. In looking at the table, you might see that there are two groups of substituents. In organic chemistry, a directing group dg is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent. Substitution of halogen onto a benzene ring cannot be halogenated by free radical mechanism organic lecture series 11. While for deactivator groups make the meta position the most negative charge. In contrast, extending the same approach to achieve activation of the distal meta. These groups are often referred to as deactivating groups because they slow down the reaction. Mechanistic studies suggested that this protodeboronation proceeds through the coordination.
In the diagram, these positions are marked r and ortho. Multiple multiple substituent substituent effects pdf. So we added a nitro group onto the meta position on our benzene ring. On the contrary, the disilylation of meta substituted bromobenzenes was not efficient or even failed in some cases and hence monosilylated derivatives.
No2, cn, so3h, cho, cor, co2h, conh2 because of the full or. The amino group is a highly activating ortho directing group and the sulfonamide group is a meta directing group. The reactivity and regioselectivity of this category of reactions is significantly impacted by the group that is already attached to the aromatic ring. The first three examples have two similar directing groups in a meta relationship to each other. The prefixes derive from greek words meaning correctstraight, followingafter, and similar, respectively. Orthopara and meta groups on ring which takes precedence. In an electrophilic aromatic substitution reaction, existing substituent groups on the aromatic. Test your knowledge on this science quiz to see how you do and compare your score to others. Protodeboronation of ortho and paraphenol boronic acids and. All electrondonating groups are activating groups and all are orthopara directors. Orthoparadirecting groups and metadirecting groups. Reaction mechanism 07 electrophilic substitution 03. Selectivity between the sites is often decided by steric effects. Orthopara directing activating by inductive effect.
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