Resonance electron withdrawal

The iV,A/,ALtrimethylammonium group, -N(CH3)3, is one of the few groups that is a meta-directing deactivator yet has no electron-withdrawing resonance effect. Explain. 

The inductive effect in 4-hydroxybenzoic acid is electron withdrawing, but this is a modest effect compared with the electron-donating resonance effect. This significantly destabilizes the conjugate base, and 4-hydroxybenzoic acid (p a 4.6) is less acidic than benzoic acid. The last example, 4-acetylbenzoic acid, is the most acidic of the group, and this is primarily the result of an electron-withdrawing resonance effect, though there is also a favourable inductive effect. 

Protons on the/3 carbon of an a,/3-unsaturated carbonyl compound absorb at very low fields j (about 57) because of the electron- withdrawing resonance effect of the j carbonyl group. 

Note that subscituents with an electron-withdrawing resonance effect have the general structure -Y-Z, where the Z atom is more elertaronegative thanY... 

Draw all resonance structures for each compound and use the resonance structures to determine if the substituent has an electron-donating or electron-withdrawing resonance effect. 

Problem 16.7 Write resonance structures for nitrobenzene to show the electron-withdrawing resonance effect of the nitro group. 

The carbonyl group whose carbon is most electrophilic, or more aptly electron-deficient, would be the site of the nucleophilic attack.The attack would have to occur at the carbonyl group para to the nitro substituent since only here will the nitro functionality exert its electron-withdrawing resonance effect as well as its inductive effect. This resonance effect can put positive charge on the carbon para to the nitro group. This positively charged carbon will make the adjacent carbonyl carbon more electrophilic. 

In contrast an electron-withdrawing resonance effect is observed in substituted benzenes having the general structure C5H5-Y=Z, where Z is more electronegative than Y. For exam-... 

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