Solution structure of some lambda(3) Iodanes: an (17)O NMR and DFT study.

The structure of a series of I-O bonded bis(acyloxy)iodoarenes and benzoiodoxolones in chloroform solution has been investigated by 17O NMR spectroscopy and by density functional theory (DFT) calculations, employing the PBE0 functional together with the LANL2DZ basis set extended with polarization (d) and diffuse (p) functions. This combined approach allowed us to ascertain that, although these classes of lambda(3) iodanes maintain in chloroform solution their solid state "T-shaped" structure, a degenerate [1,3] sigmatropic shift of iodine between the two oxygens of the acyloxy groups occurs in solution. The energy barrier involved in this process differs in the two classes, thus causing significant differences in the 17O NMR spectra, at room temperature, of the two classes of compounds.

17O NMR spectra of alpha-diesters.

17O NMR spectra of title compounds were measured at natural abundance in acetonitrile solutions. Intercarbonyl dihedral angles have been estimated by molecular mechanics, which show invariance except in one case. Because of this invariance, contrary to other alpha-dicarbonyl compounds, a correlation between chemical shifts and dihedral intercarbonyl angles could not be developed.