ENDOR spectroscopy of ion pairs derived from tropones and alkali metals: evidence for stereoisomerism
Abstract
ESR and ENDOR/TRIPLE resonance studies are reported for the ion pairs derived from the non-planar ketyls of tribenzotropone (1), dibenzotropone (2) and dibenzosuberone (3) with different alkali metal cations. The observation of three different alkali hyperfine splitting constants (hfs) in some ENDOR spectra may indicate the presence of three different stereoisomers of these ion pairs. All hfs data and their temperature dependence can be interpreted in terms of three different ion pair structures. The proton hfs are well interpreted in terms of McLachlan's spin-density calculations. Support for the geometries proposed for the three stereoisomers is provided by INDO calculations of the spin densities at the lithium cation.