The structures of LiAsF6/DMC and LiAsF6/PC solutions have been investigated at 300 K by infrared and Raman spectroscopies in the 4000-200 cm(-1) wavenumber range using various salt concentrations. A dissociation of the lithium salt into its ionic species, Li+ and AsF6-, occurs in PC solutions. In DMC solutions, analysis of the v(3) AsF6- mode reveals the presence of contact ion-pairs Li+...AsF6-, free AsF6- ions, solvated ion-pairs [Li(DMC)(4)](+) AsF6-, and polymeric ion-pairs (Li+...AsF6-)(x) when the salt concentration changes from 0.1 to 4.5 mol dm(-3). Moreover, we have shown that the conformational equilibrium of DMC was modified by the solvation of lithium ions strongly increasing the amount of the minor conformer.