NMR of terminal oxygen. Part 12. SO2and isoelectronic compounds with a true π-bond:17O NMR spectra of sulfinylamines R–NSO and sulfines RR′CSO. The conformation of ortho-substituted diaryl sulfines

The 17O NMR shift values δo of 20 sulfinylamines R–NSO 2 and of 14 sulfines RR′CSO 3(R and R′ mostly arene groups) were compared with those of the isoelectronic SO21. They show δo at much lower field than practically all other classes of S–O compounds; at the same time they exhibit the high substituent sensitivity which is typical for true πp bond systems, and absent in S+–O– compounds. The difference is discussed in terms of bond order and electronic excitation energy. Comparison of the E- and Z isomers of O-methyldiaryl sulfines yields the conformation of these compounds: one arene ring is (nearly) coplanar with the CSO group and the other (nearly) perpendicular to it. This demonstration for the molecules in solution is supported by an X-Ray structure determination.