Preferred conformations in the solid state of some alpha-(p-phenylsulfinyl)-p-substituted acetophenones

Information on the geometrical structures of alpha-(p-phenylsulfinyl)-p-substituted acetophenones X-PhC(O)CH2S(O)Ph-Y [X = OMe, Y = H (1); X = NO2, Y = OMe (2); X = OMe, Y = NO2 (3); IUPAC names: (1) 4-methoxyphenyl phenylsulfinylmethyl ketone; (2) 4-nitrophenyl 4-methoxyphenylsulfinylmethyl ketone; (3) 4-methoxyphenyl 4-nitrophenylsulfinylmethyl ketone] have been obtained from X-ray diffraction analyses. A comparison of these results with those previously obtained from X-ray diffraction and ab initio computations of alpha-methylsulfinylacetophenone, PhC(O)CH2S(O)Me, indicated that (1) and (2) adopt in the crystal a cis1 conformation and (3) assumes a quasi-gauche geometry. The stabilization of these conformations in the crystal is discussed in terms of the dipole moment coupling, Coulombic and intramolecular charge transfer interactions between the oppositely charged atoms of the C==O and S==O dipoles. The p-substituted benzene ring is quasi-coplanar with the sulfinyl group for (1) and (3), but is quasi-perpendicular for (2). Conjugation and repulsion between the sulfinyl sulfur lone pair and the pi-benzene ring seem to be responsible for the observed geometries.