Conformational study of substituted methyl phenyl sulphoxides. A multinuclear (1H, 13C, and 17O) approach

Abstract

A number of ring-substituted methyl phenyl sulphoxides have been examined with a multinuclear n.m.r. approach in order to obtain experimental evidence of the conformational properties of the methylsulphinyl group bonded to an aromatic ring. Measurements were performed of ¹H, ¹³C, and ¹⁷O chemical shifts and LIS (lanthanide-induced shifts) on ¹H and ¹³C, long-range ¹³C–¹H coupling constants. Each of these approaches by itself is not fully conclusive in showing the orientation of the SO bond in the different compounds examined, but by using them in combination a sound picture of the conformational behaviour of these molecules in solution can be obtained. The SO bond is thus almost coplanar with the aromatic ring in ortho-substituted compounds and oriented in the opposite direction with respect to the substituent. The twist-angle probably differs slightly as a function of the ortho-group. An increasing degree of distortion from coplanarity is found in para-substituted derivatives and ortho-disubstituted compounds. As regards ¹⁷O chemical shifts, these were found to span a smaller range than in the corresponding acetophenones.