IR νCO and νSO frequencies of some α-sulfinylacetophenones (PhC(O)CH2S(O)R: R = Me 1, Et 2, i-Pr 3, Ph 4, and t-Bu 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 C=O 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 a 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 t-butyl group is present.
Spectroscopic and theoretical studies on the conformation of some alpha-sulfinylacetophenones
DISTEFANO, Giuseppe;DAL COLLE, Maurizio;
1998
Abstract
IR νCO and νSO frequencies of some α-sulfinylacetophenones (PhC(O)CH2S(O)R: R = Me 1, Et 2, i-Pr 3, Ph 4, and t-Bu 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 C=O 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 a 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 t-butyl group is present.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
