Nitro groups, electron

Use SpartanView to compare electrostatic potential maps of benzoate anion 1 4-nitrobenzoate anion. Is the nitro group electron-donating or clcctron-withdr ing Next, compare electrostatic potential maps of phenoxidc anion and 4-nit phenoxide anion. Which is more strongly affected by the nitro group, benzoate ai or phenoxide anion Explain, using resonance structures. 

Meta Nitro Group - Electronic Influence on R is inductive... 

The treatment of conjugated systems in terms of electron systems that extend smoothly over all atoms allows the treatment of a variety of structural phenomena, as may be explained with a spedes that shows hindered rotation and with the nitro group. 

Figure 2-52. a) Two semipolar resonance structures are needed in a correct VB representation of the nitro group, b) Representation of a nitro group by a structure having a pentavalent nitrogen atom, c) The RAMSES notation of a nitro group needs no charged resonance structures. One jr-system contains four electrons on three atoms. 

This makes the nitro group a powerful electron withdrawing deactivating substituent and a meta director... 

Just as aniline is much less basic than alkylamines because the unshared electron parr of nitrogen is delocalized into the tt system of the nng p nitroamlme is even less basic because the extent of this delocahzahon is greater and involves the oxygens of the nitro group... 

A nitro group behaves the same way m both reactions it attracts electrons Reaction is retarded when electrons flow from the aromatic ring to the attacking species (electrophilic aromatic substitution) Reaction is facilitated when electrons flow from the attacking species to the aromatic ring (nucleophilic aromatic substitution) By being aware of the connection between reactivity and substituent effects you will sharpen your appreciation of how chemical reactions occur... 

Nitro C—NO2 Aliphatic ca 1560 (s) 1385-1350 (s) The two bands are due to asymmetrical and symmetrical stretching of the N=0 bond. Electron-withdrawing substituents adjacent to nitro group increase the frequency of the asymmetrical band and decrease that of the symmetrical frequency. 

Controlled-potential coulometry also can be applied to the quantitative analysis of organic compounds, although the number of applications is significantly less than that for inorganic analytes. One example is the six-electron reduction of a nitro group, -NO2, to a primary amine, -NH2, at a mercury electrode. Solutions of picric acid, for instance, can be analyzed by reducing to triaminophenol. 

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. 

In the case of nitrobenzene, the electron-withdrawing nitro group is not able to stabilize the positive charge in the complex intermediate. In fact, it strongly destabilizes die intermediate. This destabilization is greatest in the o- and />-intermediates, which place positive charge on the nitrosubstituted caibon. The meta transition state is also destabilized relative to that for benzene, but not as much as the ortho and para transition states. As a result, nitrobenzene is less reactive than benzene, and the product is mainly the meta isomer. 

The effect of the bond dipole associated with electron-withdrawing groups can also be expressed in terms of its interaction with the cationic u-complex. The atoms with the highest coefficients in the LUMO 3 are the most positive. The unfavorable interaction of the bond dipole will therefore be greatest at these positions. This effect operates with substituents such as carbonyl, cyano, and nitro groups. With ether and amino substituents, the unfavorable dipole interaction is overwhelmed by the stabilizing effect of the lone-pair electrons stabilizing 3. 

Although the nitro group plays a crucial role in most of these SrnI reactions, reactions of this type have synthetic application beyond the area of nitro compounds. The nitromethyl groups can be converted to other functional groups, including aldehydes and carboxylic acids.Nitro groups at tertiary positions can be reductively removed by reaction with the methanethiol anion.This reaction also appears to be of the electron-transfer type, with the methanethiolate anion acting as the electron donor ... 

---