Ortho, para activator

The entrance of a third or fourth substituent can be predicted by Beilstein s rule. If a substituent Z- enters into a compound C H XY, both X and Y exert an influence, but the group with the predominant influence directs Z- to the position it will occupy. Since all meta-directing groups are deactivating, it follows that ortho—para activating groups predominate when one of them is present on the benzene ring. 

Photoexcited aromatic compounds undergo substitution reactions with (non-excited) nucleophiles. The rules governing these reactions are characteristically different and often opposite to those prevailing in aromatic ground state chemistry 501a,b>, in contrast to the well known ortho/para activation in thermal aromatic substitutions, nitro groups activate the meta position in the photochemical substitution, as shown in (5.1) 502). 

Ortho-para Activation by Methoxy-(alkoxy-) Substituents. . 246... 

Ortho-para activation by methoxy-(alkoxy-) substituents... 

Summarizing the experimental data, we may say that ortho-para activation by methoxy-substituents seems at the moment to be as well established as the mete-activation by a nitro-group. In some of the cases (photocyanation) this ortho-para activation may be understood on the basis of the resonance stabilization during product... 

Oxidation of an alkylated benzene (making an aryl carboxylic acid) is a method of converting an ortho-para activator into a meta director. The reduction of a nitro group to make an aryl amine is a way of changing a meta director into an ortho-para activator. 

However, with compounds such as nitroveratrole, where the lifetime is excluded as a discriminating factor between the meta- and para-position, the results indeed indicate a higher reactivity at the meta-position (Stratenus, 1966). These systems at the same time furnish nice examples of a complementarity between the reactions in the ground state (ortho-para-activation) and in the excited state (meta-activation with respect to the nitro-group). The conception of... 

Classify the substituent—ortho, para activating, ortho, para deactivating, or meta deactivating— and draw the products. 

The lone pair on N makes this group an ortho, para activator. 

Hydroxyl, alkoxyl, and amino groups are also ortho-para activators, but ft a different reason than for alkyl groups. As mentioned in the previous sec tion, hydroxyl, alkoxyl, and amino groups have a strong, electron-donating resonance effect that is most pronounced at the ortho and para positions and that outweighs a weaker electron-withdrawing inductive effect. I... 

As mentioned above, the activators increase the reactivity of the ring than that of benzene. The substitution primarily occurs in the ortho and para positions of the ring relative to the activating group. For this reason, activators are also called ortho/para directors. Let us analyze this with an example. In the following reaction, phenol is nitrated. Notice that phenol contains a hydroxyl group (-OH) which is an ortho/para activator. So the substitution occurs at ortho and para positions with respect to the -OH group. 

The answer is C. The substituent -OH is an ortho/para activator. The resulting product is a bromine substitution product. The only choice that fits the reasoning is C. 

The answer is B. Phenol has the hydroxyl group which is an ortho/para activator. So the substitutions are more likely to be in the ortho and para positions of the ring. 

Tertiary (3°) aromatic amines react with NaNOj and HCI to afford products of electrophilic aromatic substitution. Draw a stepwise mechanism for this nitrosatlon reaction and explain why It occurs only on benzene rings with strong ortho, para activating groups. 

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