Nitro groups, conjugating effects

The electron-accepting conjugative effect of the sulfonio group is far greater than that of the sulfonyl group and even exceeds that of the nitro group, as can be observed from the... 

However, the introduction of sterically hindered substituents at the p-car bon atom of nitroalkene (42) completely changes the ring-chain tautomerism of conjugated nitroalkenes. Apparently, steric hindrance caused by two bulky Bu groups in product (42a) (Scheme 3.47) prevents effective conjugation of the jt systems of the C,C double bond and the nitro group, thus causing its deviation from the plane of the C=C bond as a result of which isomer (47a) becomes thermodynamically more favorable. 

Resonance in p-nitrophenoxide is particularly effective because the p-nitro group is directly conjugated to the oxyanion direct conjugation of these groups is absent in m-nitrophenoxide. 

Unsaturated nitro compound and nitriles do not usually suffer nucleophilic attack by enols or enolates and both are good at conjugate addition. The addition of the morpholine enamine 57 of cyclohexanone to 58 demonstrates that the nitro group is more effective than the ester at promoting conjugate addition.7... 

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