Translational motion and hydration of the symmetrical tetraalkylammonium ions in aqueous solution

The self‐diffusion coefficients of (CH3)4NCl, (C2H5)4NCl, (C3H7)4NCl, and (C4H9)NCl in aqueous solution together with the self‐diffusion coefficient of H2O in the same solutions have been measured. Comparison of the corresponding pair of diffusion coefficients showed that a rigid long‐lived hydration sphere of the cations does not exist – or that such an existence is at best very unlikely. Proton and deuteron nuclear magnetic relaxation rates of (CX3)4NCl and (C2X5)4NCl, X = H, D, in aqueous solution gave evidence for the existence of cation‐cation contact for the ion (C2H5)4N+.