ALKALI AND H ENDOR ON AROMATIC ION-PAIRS IN SOLUTION - INDO APPROACH

ESR, ENDOR, and TRIPLE-resonance experiments on ion pairs in solution formed by fluorenone ketyl and all alkali cations are reported. Besides the H-ENDOR lines, resonances from 7Li, 23Na, 85Rb, 87Rb, and 133Cs could also be detected, yielding all hyperfine coupling constants including their signs. Additionally, the 13C and 17O hyperfine interactions (carbonyl group) as a function of the alkali cations have been measured by ESR techniques on some labeled radicals. 1H, 13C, and 17O hyperfine splitting constants are also given for the electrolytically generated fluorenone ketyl (tetra-n-butylammonium counterion). The influence of different solvents and complexing agents (glyme, crown ether) on the magnitude of the counterion couplings is discussed. All hfs data and their temperature variations are interpreted in the frame of an adequate ion pair model. The changes of the electronic structure of the radical anion by formation of contact ion pairs are correlated with some intrinsic properties of the respective counterions. The possibility of the formation of free ions is discussed in some detail. Experimental results on the lithium salt are compared with those derived from INDO calculations. The influence of the solvent has also been included. © 1979 American Chemical Society.