Excess molar volumes, V E i jk , and speeds of sound, u i jk , of pyrrolidin-2-one (2-Py) (i) + benzene or methyl benzene ( j) + propan-1-ol (k) ternary mixtures and speeds of sound, u i j , of benzene or methyl benzene (i) + propan-1-ol ( j) binary mixtures have been measured dilatometrically and interferrometrically over the complete mole fraction range at 308.15 K. Speed-of-sound data have been utilized to evaluate excess isentropic compressibilities for binary and ternary mixtures. V E i jk and κ E S i jk values have been fitted to a Redlich-Kister equation to predict ternary adjustable parameters and standard deviations. Topological investigations employed for predicting excess molar volumes and excess isentropic compressibilities, κ E S i j , of 2-Py + benzene or methyl benzene or propan-1-ol binary mixtures have been extended to ternary mixtures (by employing the concept of a connectivity parameter of third degree, 3 ξ, of a molecule) to obtain an expression that describes well the measured V E i jk and κ E S i jk values.Keywords Connectivity parameter of third degree 3 ξ · Excess isentropic compressibility κ E S i jk · Excess molar volume V E i jk · Interaction energy parameter (χ ) · Speed of sound u i jk