Abstract
A METHOD for determining the association constants of organic charge–transfer complexes in solution using nuclear magnetic resonance has recently been described1,2. For a series of solutions containing an electron donor species (D) and an electron acceptor species (A) which interact by a very fast reversible process to form a 1 : 1 charge–transfer complex (DA), if one of the reactants, say D, is in large excess over the second reactant, then2 where [D]0 is the total (free and complexed) concentration of the donor, Δ is the observed chemical shift of a nucleus in A in the complexing medium relative to the shift of this nucleus in uncomplexed A, and Δ0 is the shift of this nucleus in the acceptor moiety of the pure complex, again relative to the shift in uncomplexed A. Kc is the association constant defined by Kc = [DA]/[D][A], where the concentrations represent the equilibrium values for the various species. A plot of Δ/[D]0 against Δ should yield a straight line, the gradient of which is equal to −Kc and the intercept with the ordinate equal to KcΔ0.
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References
Hanna, M. W., and Ashbaugh, A. L., J. Phys. Chem., 68, 811 (1964).
Foster, R., and Fyfe, C. A., Trans. Faraday Soc., 61, 1626 (1965).
Foster, R., and Fyfe, C. A., Trans. Faraday Soc., 62, 1400 (1966).
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FOSTER, R., FYFE, C. Simultaneous Determination of Several Charge-transfer Complex Association Constants using Nuclear Magnetic Resonance. Nature 213, 591–592 (1967). https://doi.org/10.1038/213591a0
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DOI: https://doi.org/10.1038/213591a0
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