Aromatische phosphine mit substituenten zweiter ordnung-VII

The NMR non-equivalence of the Me groups in para-substituted dimethylbenzamides depends on the solvent and the substituent: Rotation around the CN bond is increasingly hindered with growing polarity of the solvent (and even more by its ability to form H-bonds) and with increasing electron attracting properties of the substituent, the mesomeric effect being much more efficient than the inductive one. Chalcogenide and onium phosphorus, according to this method, exerts a -M effect which is comparable to that of a nitro group.