Association constants of fluoranil-methyl-benzene complexes from nmr chemical shift measurements

The association constants for a series of methylbenzene-fluoranil electron donor-acceptor complexes have been determined from NMR chemical shift measurements using 1: 1 stoicheiometric ratios of electron donor-electron acceptor. The resulting values differ from those obtained when large excess concentrations of donor are used. It is suggested that the differences may be the result of the presence of significant concentrations of termolecular complexes in the latter solutions.