Sulfilimine. II. IR, UV and NMR Spectroscopic Studies

The physical properties of several N-p-tolylsulfonylsulfilimines were studied by means of infrared, ultraviolet and NMR spectroscopic determinations. Four characteristic infrared absorption bands due to both sulfonyl and sulfilimino groups are observed and those due to both N–S(IV) and N–S(VI) stretching vibrations appear at nearly the same positions and overlap with each other. The ultraviolet spectra suggest that the sulfilimino group is not an electron donor but an electron acceptor group when conjugated with a phenyl ring and could be used to measure the pKa value of methyl-p-methoxyphenyl derivative. The NMR chemical shift of methyl protons attached to the S atom of S-methyl-S-p-tolyl derivative appears at 2.81 ppm, whereas the shifts of the corresponding sulfoxide and the sulfone groups appear at 2.69 and 3.04 ppm, respectively. From these results, it seems that the N–S(IV) bond of N-p-tolylsulfonylsulfilimine is of semipolar character while the charges on the S(IV) atom and the N atom are delocalized substantially with strong dπ conjugation into S(IV)–N–S(VI) bondings.