A Study of steric and electronic effects in some methane‐ and dimethane‐sulphonanilides by ¹³C NMR spectroscopy

The steric and electronic interactions in several methanesulphonanilides and dimethane‐sulphonanilides have been examined on the basis of their ¹³C NMR chemical shifts. In aromatic amines there is evidence of nitrogen electron pair donation into the aromatic ring. However, the substitution of a methanesulphonyl group on nitrogen, as in N‐phenylmethanesulphonamide, causes a decrease in this resonance interaction. The chemical shifts of ortho‐ and para‐carbons therefore move downfield in comparison with the corresponding amines. Substitution of the aromatic ring at the para position by electron‐withdra wing and electron‐donating groups affects the resonance process. The substitution of methyl groups either at nitrogen or at the ortho positions causes severe steric inhibition of resonance, which is clearly reflected in the chemical shifts of these compounds. The chemical shifts in several dimiethane‐sulphonanilides have also been examined and compared with the shifts in the corresponding methanesulphonanilides. The observed differences are explained in terms of steric, mesomeric and inductive interactions in these molecules. The preferred conformations of these compounds in solution are also postulated on the basis of their chemical shifts.