Nitro group electron-withdrawing effect

Nucleophilic Displacement Reactions. The strong electron-withdrawing effect of a trifluoromethyl group activates ortho and para halogen toward nucleophilic attack. Such chlorine labiUty is utili2ed in the manufacture of crop control chemicals containing trifluoromethyl and nitro groups. 

Much of the reactivity shown by the ring atoms and substituents of pyrimidine is akin to that of the corresponding parts of 1,3-dinitrobenzene and 3-nitropyridine. This arises from the quantitatively similar electron-withdrawing effects of doubly-bound ring nitrogen atoms and of nitro groups in reducing sharply the aromaticity of the cyclic system. 

The behavior of aminopyrazole 88 (R = 4-NO2—C6H4) under these conditions was quite different diazotization using nitrous acid in concentrated hydrochloric acid afforded an alkynylpyrazole diazonium chloride, which did not participate in the Richter reaction, probably due to the electron-withdrawing effect of the nitro group. Instead, after neutralization of the hydrochloric acid with sodium hydrogen... 

Nitration differs from halogenation since here the strongly electron-withdrawing effects of the nitro substituents first introduced influence the reactivity and the positions of further introduced substituents. Therefore, it is possible to prepare under carefully controlled reaction conditions different substitution products.100 103 The preparation of the tetrasubstituted product cannot be achieved since the deactivating effects of three nitro groups are too strong.104... 

Due to electron withdrawing effect of nitro group and electron releasing effect of methoxy group. 11.20 (i) Hydration of Propene. 

Though not available commercially, trifluoronitroethane shows some interesting chemistry consistent with the powerful electron-withdrawing effect exerted by the nitro group. Fluoride-mediated nitroaldol reactions were reported [144] with aldehydes affording a valuable entry to trifluoromethyl amino alcohols... 

The electron-withdrawing effect of pentazole is similar to a nitro group and the H NMR shifts of nitrophenyl and pentazolylphenyl compounds are similar <2002ZFA1933>. The 7i-electron densities calculated by the Hiickel molecular orbital (HMO) method show a linear correlation with 111, 13C, and 14N NMR chemical shifts in the azole series <1977IJB168>. The 1SN NMR chemical shifts of the following compounds have been reported cesium/tetramethyl ammonium (TMA) pentazolylphenolate (8 —81.1 (N-l), —29.7 (N-3/N-4), 1.9 (N-2/N-5)) <2002AGE3051> ... 

This time there is no resonance structure that has the positive charge on the carbon bonded to the nitro group. The arenium ion is still destabilized by the electron-withdrawing effect of the nitro group, but this ion is not destabilized as much as the ion produced by attack of the electrophile at the ortho position because the positive charge is never as close to the nitro group. 

The resistance of pyridine toward electrophilic substitution is well known, and this reluctance to react is enhanced in the protonated species. Incorporation of extra annular nitrogen atoms further decreases this reactivity with electrophiles each aza substituent has an electron-withdrawing effect similar to a nitro group. One estimate of the o value for an aza substituent (=N—) is 0.65, and 1.95 for the protonated species (=N + H—) [68JCS(B)1484] (see also Chapter 9, Sections 9.A-9.C). Val-... 

In the examples shown below, notice that a nitro substituent (electron-withdrawing) increases the strength of the acid, while a methoxy substituent (electron-donating) decreases the acid strength. The nitro group has a larger effect in the ortho and para positions than in the meta position. 

Note carefully that this is an inductive effect there are no arrows to be drawn to show how fluorine withdraws electrons—It does it Just by polarizing C-F bonds towards itself. Contrast the electron-withdrawing effect of the nitro group, which works mainly by conjugation. 

The insertion of nitro group into 2-trichloromethylbenzimidazole raises the 35C1 NQR average frequency due to electron-withdrawing effect of N02 despite its remoteness from the indicator atom [1407],... 

The reaction of 3-bromo-4-nitroquinoline 1-oxide (220) with 1-morpholinocyclohex-ene 14 gave furoquinoline 228 after treatment with base (equation 48)118. It was demonstrated that the reaction proceeds via a multistep ionic process involving the initial formation of 225 via 221-224 followed by a base-catalyzed enolization to 226 and cyclization to 227 and 228. Apparently, the strong electron-withdrawing effect of the nitro group is essential for the reaction to occur, because similar compounds without the nitro group do not undergo this conversion. 

Nitrostyrenes are easily polymerized anionically, basically due to the strong electron-withdrawing effect of the nitro group on the double bond, both by induction and resonance effects. The double bond is electron-deficient and susceptible to nucleophilic attack. Carter et al. [117] synthesized and polymerized a number of substituted nitrostyrenes and measured their reactivity. Their results are summarized in Table 6. 

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