Mobility of alkyl chains in quaternary ammonium salts

Selective 13C relaxation times have been measured in the tetraalkylammonium ions of general formula N(Rm )4 +, with m = 1, 2, 3, 4, 6 and 8 carbon atoms. The experimental data are related to the frequencies of the conformational transitions involving specific carbon atoms, averaged over the possible conformations of the moving chain. The transition rates are calculated from a detailed model of random walk among conformational sites, requiring computation of the geometry-dependent hydrodynamic friction and the cooperative effects resulting from coupling of the rotational coordinates.