1H and 13C NMR study of substituent effects in 2- and 3-substituted diphenyl sulphides and sulphones and 4-substituted 2′,6′-dimethyldiphenyl sulphides

The proton and carbon NMR spectra of nine 2‐substituted diphenyl sulphides (S‐2‐X), seven 3‐substituted diphenyl sulphides (S‐3‐X), nine 2‐substituted diphenyl sulphones (SO2‐2‐X), nine 3‐substituted diphenyl sulphones (SO2‐3‐X) and nine 4‐substituted‐2′,6′‐dimethyldiphenyl sulphides (Me2‐S‐4‐X) were obtained. Correlations of the 1H and 13C chemical shifts were made with benzene substituent‐induced chemical shifts (Lynch plots) and Hammett and dual‐substituent parameters and the results were compared with those of 4‐substituted diphenyl sulphides (S‐4‐X) and sulphones (SO2‐4‐X). The main conclusions are as follows: (i) the transmission of the substituent effects in substituted diphenyl sulphides decreases in the order S‐4‐X ≈︁ S‐2‐X > Me2‐S‐4‐X > S‐3‐X; (ii) the inductive effects are transmitted to a larger extent than the resonance effects to the unsubstituted ring in 3‐substituted diphenyl sulphides, while the reverse trend is observed in other substituted diphenyl sulphides; (iii) in 2‐methoxy‐, 2‐chloro‐, 2‐bromo‐ and 2‐nitrodiphenyl sulphides, an increase in the size of the substituent causes an upfield shift for H‐6 ascribable to the repulsion between the lone pairs of electrons on the sulphur and the substituent and its influence on the conformation; (iv) the diminished transmission of substituent effects to the remote rings in 4‐substituted 2′,6′‐dimethyldiphenyl sulphides is probably due to the orthogonal orientation of the rings; and (v) the signal due to the H‐6 of 2‐substituted diphenyl sulphones suffers a downfield shift with an increase in the size of the substituent, this being ascribable to the increasing steric interaction between the 2‐substituent and the sulphonyl oxygen and consequent changes in the conformation.