H-1 AND C-13 NMR-STUDY OF SUBSTITUENT EFFECTS IN 2-SUBSTITUTEDAND 3-SUBSTITUTED DIPHENYL SULFIDES AND SULFONES AND 4-SUBSTITUTED 2',6'-DIMETHYLDIPHENYL SULFIDES

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 (SO2-3X) and nine 4-substituted-2',6'-dimethyldiphenyl sulphides (Me(2)-S-4-X) were obtained. Correlations of the H-1 and C-13 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 approximate to S-2-X > Me(2)-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.