Illustrated glossary of organic chemistry orthopara. Orthopara or meta directing book f 6 e,hcl or sn, hcl no2 nh2 activating orthopara 19. The amino group is a highly activating orthodirecting group and. H bond functionalisation of substrate 20 and directing group removal of functionalised product 21 can be carried out in onepot. The other group reacts to makemostly metasubstituted products. We predicted orthopara and meta group directing behaviors for a list of groups whose. The first exercise is to make sure you know which groups are activators and deactivators as well as how that relates to the ortho. Why is benzoic acid a meta directing group answers. If the opposite is observed, the substituent is called a meta directing group.
H activationborylationoxidation protocol for the preparation of phenols is described. For example, the chlorination of toluene gives an o p ratio anywhere between 62. The nature of orthopara and meta group directing in electrophilic aromatic substitution article pdf available in the journal of chemical physics 14119. Nitration of arenes bearing orthopara directing groups. For example, x, o, oh, or, ocor, nh2, nhr, nhcor etc. H activation has been known for the last few decades. As shown in figure, the orthopara addition will give a resonance structure that puts the carbocation adjacent to a partially positive charged atom. 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. Orthopara and meta groups on ring which takes precedence. Spencer and igor larrosa while several methods for the ortho selective arylation of. Substituents that cause this effect are called o,p directors hno 3 h2so 4 anisole activated ring and they usually activate the ring. Type 2 all groups having their key atom multiply bonded to more powerful element are meta dir. H bonds in aromatic molecules remained elusive for a long time.
In the following example, the chloro group is an ortho, paradirecting group. Orthopara directing groups are often believed to donate a portion of their electron density to the aromatic ring, whereas meta directing groups usually are. In some cases, the directing group introduction can also be done in the same pot. King chapter 18 electrophilic aromatic substitution i. Activatingdeactivating, orthoparameta substituents. Myers directed ortho metalation chem 115 harvard university. In an electrophilic aromatic substitution reaction, existing substituent groups on the aromatic. Bromination of nitro benzene gives metabromonitro benzene as the major product because the nitro group is a meta director. It also provides regioselective access to the nitro. Directing group influence an atom or group already attached to a benzene ring may direct an incoming electrophile to either the ortho. Meta directing groups the meta directing groups in table 16. Indeed, it depends greatly on the conditions of the reaction. Ortho, paradirecting groups are groups whose presence in the benzene ring activates it for further electrophilic substitution.
In the previous post we introduced ortho,paraand metadirectors in electrophilic aromatic substitution. The resulting amide can be used for a second metalation reaction o o oconet 2 o o o net 2 o o o o net 2 o oh nh o h ho oh oh oh cho pancratistatin 1. When the directing effects of substituents and the ring compete, it is not unusual to observe. Cf 3, no 2, cn, donation or withdrawal of electrons can occur via either a conjugative or an inductive effect.
Arene substitution patterns are part of organic chemistry iupac nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. There are also electron donors serving as meta directing groups. The prefixes derive from greek words meaning correctstraight, followingafter, and similar, respectively. Substituents stabilize positive charge on substituted carbon. Meta directors predominantly direct the incoming group to a position meta to itself. No2, cn, so3h, cho, cor, co2h, conh2 because of the full or. Now, if the meta director is meta to the orthopara director, youre probably going to get a mix of every position, because the meta directing deactivation will be offset by the donating groups donating of electrons to the same spot. Meta direction groups video organic chemistry tutorial video. Weakly deactivating groups direct electrophiles to attack the benzene molecule at the orthoand parapositions, while strongly and moderately deactivating groups direct attacks to the metaposition. Working on the concept of democratisation of education. Oct 03, 2017 discuss doubts with iit jee aspirants on our online jee prep portal like vineet khatri sir on facebook.
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. Protodeboronation of ortho and paraphenol boronic acids and. This is video 11 in the electrophilic aromatic substitution video series. Type 2 all groups having their key atom multiply bonded to more powerful element are metadir. This is a part of a detailed tutorial video series. 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. Atoms or groups that make the benzene molecule more reactive by increasing the rings electron density are called activating groups. We report a new methodology, based on the traceless directing group relay concept. Myers directed ortho metalation chem 115 carbamate directing groups can rearrange upon warming after lithiation. While there is nothing especially good about the meta pathway, it is relatively lower in energy than the orthopara pathways. Metadirecting groups the metadirecting groups in table 16. Orthopara directors alkyl substituents are electrondonating groups and they are activating groups. The amino group is a highly activating ortho directing group and the sulfonamide group is a meta directing group. Orthopara directing deactivating by inductive effect stabilizing resonance.
Two substituents in a 1,2 relationship are said to. In contrast, extending the same approach to achieve activation of the distal meta. Electrophilic aromatic substitution electrophilic aromatic. The first metalfree thermal protodeboronation of ortho and paraphenol boronic acids in dmso was developed. Nitration of bromobenzene gives a mixture of orthobromonitro benzene and parabromonitro benzene as the major products because the bromine substituent is an orthopara director.
Several methods exist in order to separate these isomers. Protodeboronation of ortho and paraphenol boronic acids. Discuss doubts with iit jee aspirants on our online jee prep portal like vineet khatri sir on facebook. Such directing groups are classified as removable or modifiable.
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