Proton self‐exchange of para‐substituted N,N‐dimethylanilines and their conjugate acids in aprotic solvents

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Abstract
The intermolecular proton transfer between the title compounds was investigated by dynamic NMR spectroscopy. The mechanism was found to be direct proton transfer, other transfer pathways being excluded by the experimental conditions (aprotic solvents with an extremely low water content of about 5×10−4M). It was shown that the observed exchange rates are identical with the rates of the proton transfer proper; association or dissociation pre‐ or postequilibria are not rate determining. Magnitude and solvent dependence of the kinetic isotope effects, as well as the influence of the solvent polarity on the intrinsic activation barrier ΔG‡int indicate considerable solvent reorganization during the transfer. These observations, as well as correlations between the activation parameters of proton self‐exchange and electron self‐exchange of the substrates studied provide some evidence that inner‐sphere and outer‐sphere contributions to ΔG‡int might be separable.