Density (rho), refractive index (n(D)) and speed of sound (u) values are measured for the binary mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and 2-pyrrolidone over the entire range of mole fraction at temperatures from (298.15 to 323.15) K under atmospheric pressure. Using the basic experimental data, molar volume (V-m), isentropic compressibility (k(s)), intermolecular free length (L-f), molar refraction (R-m), excess molar volume (V-m(E)), excess isentropic compressibility (K-s(E)) and excess intermolecular free length (L-f(E)) values are calculated. The calculated properties are discussed in terms of molecular interactions between the present investigated system. The excess values are fitted to Redlich-Kister polynomial equation to estimate the binary coefficients and standard deviation between the experimental and calculated values. Further, the molecular interactions in the binary mixture system are analysed using the experimental FT-IR spectrum recorded at room temperature. (C) 2015 Elsevier Ltd. All rights reserved.