The conformation of diphenyl sulphone and 3,4'-dichlorodiphenyl sulphone has been studied by the lanthanideinduced shift (LIS) technique. The lanthanide-sulphone complexation model was established using the conformationally rigid dibenzothiophene sulphone molecule. Several models were tried, including both monodentate and bidentate coordination of oxygen to lanthanide. Poor results were obtained for the bidentate models, but three different monodentate models (one-, two-and three-site) all gave reasonable solutions. The binding position in the three-site model was established using the program LIRAS4, an adaptation of LIRAS3, with an Ln-0 geometry having R and q5 values of 2.8 A and 150° being suggested. Site populations were 16%, 42% and 42% in sites 1 , 2 and 3, respectively.
Diphenyl sulphone has insufficient data (AM values) for a complete analysis, but the more extensive data set for 3,4'-dichlorodiphenyl sulphone allowed a full analysis which indicated a preferred twist angle of the phenyl rings (6) of No, using all the monodentate models. However, the three-site model produced significantly lower errors in the predicted shifts and also suggested an identical lanthanide position to that found for dibenzothiophene sulphone. Site populations were 0%, 50% and 50% in sites 1, 2 and 3, respectively, the zero occupancy of site 1 being rationalized in terms of steric interactions with the H-1 protons. Preferential binding of the shift reagent to the S=O bond trans to the meta-chlorine atom (65%) was observed.