This work presents the synthesis of a series of new protic ionic liquids (PILs) based on the methylpropylammonium cation with sulfate, methanesulfonate, and bis(trifluoromethanesulfonyl)imide anions, as well as a salt composed of the tripropylammonium cation and the methanesulfonate anion. Their thermal properties, electrical conductivity, and viscosity were thoroughly investigated. The transport properties and Walden plots were analyzed to elucidate the conduction mechanisms possible in these PILs. The obtained characteristics were compared with literature data for salts containing other propylammonium-based cations. To gain deeper insight into their properties, we complemented experimental measurements with computational methods. The analysis of their thermal behavior and the calculation of molar conductivity were supported by quantum chemical calculations at the B3LYP-GD3/6–31++G(d,p) level of theory. These computations determined the Gibbs free energy of ion pair formation, cation-anion interaction energies, and van der Waals volumes. Furthermore, correlation equations were established between the experimental molar volumes of the PILs and the computed sums of the van der Waals volumes of the corresponding ions.
