Spectroscopic and theoretical studies on the conformation of some α-sulfinylacetophenones

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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


Abstract

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 cisgauche population ratio in solvents of increasing polarity for compounds 1–4 support the existence of a strong intramolecular interaction between C[double bond, length half m-dash]O and S[double bond, length half m-dash]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[double bond, length half m-dash]O and S[double bond, length half m-dash]O dipoles along with the π*S[hair space][double bond, length half m-dash][hair space]O←nO(CO) charge transfer which lead to an O(CO)[hair space][hair space]· · ·[hair space][hair space]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.


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