Ion-Solvent Interaction of Tetraalkylammonium Ions in Solvents of High Dielectric Constant. II. Conductance and Walden Product of Tetraalkylammonium Ions in N-Methylformamide and N-Methylpropionamide at Different Temperatures

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Ion-solvent interaction of the tetraalkylammonium ions (R4N+) in N-methylformamide and N-methylpropionamide has been investigated from the electrical conductance point of view. It appears that the R4N+ ions act as net structure breakers in these solvents as in N-methylacetamide. The appreciable negative deviation of the experimental slope of the Λ vs. \sqrtc curves from the theoretical slope suggests some kind of obstruction to the movement of the R4N+ ions, probably due to their unwieldy size or to some kind of cation-anion association, although the usual kind of association is ruled out in view of the high dielectric constant of these solvents. The cation-anion interaction may be the penetration of the cations by the anions which has been suggested as a possible reason for the negative slope in the apparent molal volume vs. \sqrtc curves, obtained at higher concentrations, to which apparent molal volume measurements usually have to be confined on account of difficulties in accurate density measurements at low concentrations. The smaller alkali metal ions appear to be more solvated than the R4N+ ions, so much so that the λ0+-values of Na+ and K+ ions are lower than the corresponding values of the Me4N+ and Et4N+ ions.
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