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

Abstract

¹H NMR spectra have been recorded for r(2),c(6)diphenylthian-4-one <b>1</b>, t(3)-methyl-r(2),c(6)-diphenylthian-4-one <b>2</b>, c(3)-methyl-r(2),t(6)-diphenylthian-4-one <b>3</b> and their 1,1-dioxides 4-6 at 270 MHz. For <b>3</b> NOESY spectrum also has been recorded. <b>AMI</b> calculations have been performed on <b>1</b>, <b>3</b> and <b>4</b>. It seems that conformation <b>3AC</b> with one axial methyl

group and one axial phenyl group should contribute to some extent to <b>3</b> in solution. <b>AM1 </b>calculations suggest that conformation <b>3AC</b> and boat conformation <b>3B</b> have almost same energy and lie 1 kcal mol^-1 above the chair conformation <b>3C</b>. The calculations suggest that boat form could at best contribute to the extent of 4% to <b>1</b>. In the sulphones the <i>J_aa </i>values are unusually large. The torsional angles are calculated using DAERM method and Altona's equatIOn. The results suggest that both methods are equally successful for sulphides but Altona's equation is not statisfactory in calculating ϕ_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 ¹H chemical shifts of <b>1-6</b> are analysed in some detail. It is found that an axial phenyl group deshields an adjacent axial proton by 0.6 ppm.