Deactivating groups

Deacon equilibrium Deacon process Deacon reaction Deactivating groups Deactivation... 

The pKa of p-(tiifluoromethyl)benzoic acid is 3.6. Is the trifluoromethyl substituent an activating or deactivating group in electrophilic aromatic substitution ... 

Decide whether p-ftrifluoromethvUbenzoic acid is stronger or weaker than benzoic acid. A substituent that strengthens the acid is a deactivating group because it withdraws electrons, and a substituent that weakens the acid is an activating group because it donates electrons. 

A pKa of 3.6 means that p-(trifluoromethyl)benzoic acid is stronger than benzoic acid, whose pKa is 4.19. Thus, the trifluoromethyl substituent favors dissociation by helping stabilize the negative charge. Trifluoromethyl must therefore be an electron-withdrawing, deactivating group. 

Deactivating group (Section 16.4) An electron-withdrawing substituent that decreases the reactivity of an aromatic ring toward electrophilic aromatic substitution. 

Aniline does not undergo Frledel-Crafts reaction (alkylation and acetylation) due to salt formation with aluminium chloride, the Lewis acid, which Is used as a catalyst. Due to this, nitrogen of aniline acquires positive charge and hence acts as a strong deactivating group for further reaction. 

Usual problems for the application of the PFR to organic synthesis are the occurrence of competing photochemical reactions (like trans-cis isomerization) or the presence of deactivating groups in the phenolic ring. In this subsection, it will be shown how these problems can be circumvented. 

For the aromatic carboxylic acids, substituents on the aromatic ring may also influence the acidity of the acid. Benzoic acid, for example, has = 4.3 x 10 . The placements of various activating groups on the ring decrease the value of the equilibrium constant, and deactivating groups increase the value of the equilibrium constant. Table 12-2 illustrates the influence of a number of para-substituents upon the acidity of benzoic acid. 

Para-Substituted Benzoic Acid, Deactivation Groups K Value a... 

Mo catalysts are uniquely effective in the polymerization of S-containing disubstituted acetylenes. Though there is a possibility that S and O in the monomer deactivate group 5 and 6 transition metal catalysts, the basicity of S is weakened by the conjugation with the triple bond, resulting in the lower coordinating ability to the propagating... 

A deactivating group (electron-withdrawing) directs electrophiles into the other ring, usually at a positions. 

Side chain is oxidized when a deactivating group (NO,) rather than an activating group (NH,) is attached to ring. 

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