Dynamic NMR as a Nondestructive Method for the Determination of Rates of Dissociation. V. Proton Affinities of p-Substituted N,N-Dibenzylanilines in Aprotic Solvents

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Abstract
Rates of proton exchange between p-substituted N,N-dibenzylanilinium ion and chloride ion in chloroform-d and acetonitrile-d3 were determined by the dynamic NMR technique. Comparison of the kinetic proton affinity of the anilines in the aprotic solvents with the proton affinity of anilines in the gas phase and the basicity in water revealed that they could be linearly correlated. The feature of the kinetic data was a large positive entropy of activation which can be ascribed to the change from an ionic ground state to a covalent transition state. The entropy of activation was somewhat smaller in acetonitrile-d3 than in chloroform-d. This was attributed to the change in the stage of the transition state for the exchange. A small amount of water which could not be removed easily from the aprotic solvents was proved not to harm the results.