Deactivating groups, aromatic nitro

A nitro group deactivates an aromatic ring to electrophilic attack, but it activates the ring towards nucleophilic substitution. 

The aromatic nitro group is a deactivating substituent as far as electrophilic aromatic substitution is concerned. Further electrophilic substitution requires vigorous conditions and takes place at the least deactivated position. Thus the preparation of 2,4,6-trinitrotoluene (TNT) from 4-nitrotoluene requires fuming nitric acid and fuming sulfuric acids. Nitrobenzene is sufficiently unreactive towards electrophilic substitution to be used as a solvent for the Friedel-Crafts alkylation of more reactive aromatic systems. 

Derivatives.—Arylhydrazon.es having electron-attracting groups such as p-nitro that deactivate the aromatic ring may undergo electrophilic... 

The OH radical reaction rate constants with 1- and 2-nitronaphthalene and that of 2-methyl-1-nitronaphthalene are significantly lower than that for the parent PAH naphthalene [A (OH + naphthalene) = 2.3 x 10 , fe(OH- -1-methylnaphthalene) = 5.3 X 10 and fe(OH + 2-methylnaphthalene) = 5.23 x 10 cm molecule s (Calvert et al., 2002)]. As mentioned earlier for other nitro-containing compounds, this shows that substitution of an — N02 group on the aromatic ring markedly deactivates the aromatic ring to electrophilic addition of the OH radical. A similar situation is observed for the monocyclic aromatics, with the ambient temperature rate constant for the reaction of the OH radical with nitrobenzene being a factor of 10 lower than that for benzene. 

Neither Friedel-Crafts acylation nor alkylation reactions can be earned out on mtroben zene The presence of a strongly deactivating substituent such as a nitro group on an aromatic ring so depresses its reactivity that Friedel-Crafts reactions do not take place Nitrobenzene is so unreactive that it is sometimes used as a solvent m Friedel-Crafts reactions The practical limit for Friedel-Crafts alkylation and acylation reactions is effectively a monohalobenzene An aromatic ring more deactivated than a mono halobenzene cannot be alkylated or acylated under Friedel-Crafts conditions... 

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