NMR of terminal oxygen. Part 12. SO2 and isoelectronic compounds with a true π-bond: 17O NMR spectra of sulfinylamines R–NSO and sulfines RR′CSO. The conformation of ortho-substituted diaryl sulfines

Abstract

The ¹⁷O NMR shift values δ_o 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 δ_o 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 π_p 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.