1H NMR spectral study of some 2,6-diphenylthian-4-ones and their 1,1-dioxides

H-1 NMR spectra have been recorded for r(2),c(6)diphenylthian-4-one 1 t(3)-methyl-r(2),c(6)-diphenylthian-4-one 2, c(3)-methyl-r(2),t(6)-diphenylthian-4-one 3 and their -1.1-dioxides 4-6 at 27.0 MHz. For 3 NOESY spectrum also has been. recorded. AMI calculations have been performed on 1, 3 and 4. It seems that conformation 3AC with one axial methyl group and one axial phenyl group should contribute to some extent to 3 in solution. AM1 calculations suggest that conformation 3AC and boat conformation 3B have almost same energy and fie 1 kcal mol(-1) above the chair conformation 3C. The calculations suggest that boat. form could at best contribute to the extent of 4% to 1. In the sulphones the J(aa) values are unusually large. The torsional angles are calculated using DAERM method. and Allona's equation. The results suggest that both methods are equally successful for sulphides but Altona's equation is not statisfactory in calculating phi(aa) values in sulphones. Comparison of the results with those-obtained from X-ray crystallographic studies suggests that proton-proton torsional angles in the solid state may considerably differ from those in solution. The H-1 chemical shifts of 1-6 are analysed in some detail. It is found that an axial phenyl group deshields an adjacent axial proton by 0.6 ppm.