The Conformations of Several 1-Phenylethyl and 1-Phenylpropyl Aryl Sulfoxides. Evidence for Attractive Aryl/Aryl Interaction

The conformations of the diastereoisomers of 1-phenylethyl phenyl (1), 1-phenylethyl p-tolyl (2), 1-phenylpropyl phenyl sulfoxides (3) were studied by NMR spectroscopy, largely by means of the computer simulation of the lanthanoid-induced shifts. It has been suggested that the rotamer in which the aromatic group (Ar) is 4C_6H_5CH(R)–SO–Ar& 1:R=& &CH_3,& Ar=&C_6H_5 & 2:& &CH_3,& &C_6H_4CH_3(p) & 3:& &C_2H_5,& &C_6H_5 gauche to the phenyl (Ph) and anti to the alkyl (R) group is most populated in the conformational equilibria of (RS/SR)-1, 2, 3, and (RR/SS)-3. For (RR/SS)-1 and 2, on the other hand, the most important contributor has been suggested to be the rotamer in which Ar is flanked by Ph and R. The results have been discussed in the light of the presence of attractive interactions between relevant groups.