The thermodynamic parameters viz. excess molar volume V-E and speed of sound u, transport parameter viscosity eta, and spectroscopic parameters viz. IR, H-1, C-13 NMR have been measured for the mixtures of isomeric butanediol (1,2-, 1,3-, 1,4-, and 2,3-butanediol) and N-methyl-2-pyrrolidinone over the whole composition range at 308.15 K. The partial molar quantities Q(i)(E), isentropic compressibility K-S(E), viscosity deviation Delta eta, deviation in Gibbs free energies of activation for viscous flow g(x), and excess NMR chemical shift delta(E) have been estimated and analyzed. Results show that the interaction between unlike molecules takes place through hydroxyl groups of isomeric butanediol and CO group of N-methyl-2-pyrrolidinone. Excellent agreement between thermodynamic and spectroscopic measurements is observed. (C) 2009 Elsevier Ltd. All rights reserved.