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

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 parasubstituted derivatives and ortho-disubstituted compounds. As regards 170 chemical shifts, these were found to span a smaller range than in the corresponding acetophenones.