Paulo R. Olivato, Mirta G. Mondino, Marcelo H. Yreijo, Blanka Wladislaw, Marcelo B. Bjorklund, Liliana Marzorati, Giuseppe Distefano, Maurizio Dal Colle, Gabriella Bombieri and Antonio Del Pra
IR νCO and νSO frequencies of some α-sulfinylacetophenones [PhC(O)CH2S(O)R: R = Me 1, Et 2, Pri 3, Ph 4 and But 5] have been measured and their conformations are estimated with the help of ab initio 6-31G** calculations and X-ray diffraction analyses. The anomalous negative carbonyl frequency shifts for the cis2 rotamer together with the decrease of the cis∶gauche population ratio in solvents of increasing polarity for compounds 1–4 support the existence of a strong intramolecular interaction between CO and S
O dipoles, which stabilizes the cis2 rotamer more than the πCO–σ*C–SO and π*CO–σC–SO orbital interactions stabilize the gauche3 rotamer. The stability of the cis2 rotamer is discussed in terms of the electrostatic attraction between the C
O and S
O dipoles along with the π*S
O←nO(CO) charge transfer which lead to an O(CO)
· · ·
S(SO) contact shorter than the sum of the corresponding van der Waals radii. The gauche2 rotamer of 5 is more stable than the cis2 one in which steric strain between the carbonyl oxygen atom and the tert-butyl group is present.