Thermodynamic properties of liquid mixtures containing cyclic amines and isomeric picolines: excess molar volumes and excess isentropic compressibilities and excess heat capacities

The present study reports densities, ρ, speeds of sound, u, molar heat capacities, CP of binary piperidine or 1-methylpiperidine (1) + 2- or 3- or 4-picolines (2) mixtures over entire composition range by varying temperature range from 293.15 to 308.15 K with step of 5 K interval. Experimental data have been used to access excess molar volumes, VE, excess isentropic compressibilities, $$\kappa_{{\rm S}}^{\text{E}}$$ and excess heat capacities, $$C_{{\rm P}}^{\text{E}}$$ . The VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ data have been fitted to Redlich–Kister polynomial equation to evaluate the adjustable parameters and standard deviations. The $$C_{{\rm P}}^{\text{E}}$$ data of piperidine (1) + 2- or 3- or 4-picolines (2); 1-methylpiperidine (1) + 3- or 4-picolines (2) are positive and those for 1-methylpiperidine (1) + 2-picoline (2) mixture, sign and magnitude of $$C_{{\rm P}}^{\text{E}}$$ values change with increase in mole fraction of 1-methylpiperidine. Further, VE and $$\kappa_{{\rm S}}^{\text{E}}$$ of 1-methylpiperidine (1) + 2- or 3- or 4-picolines (2); piperidine (1) + 2- or 3-picolines (2) are negative; and those for piperidine (1) + 4-picoline (2) are positive across full range of composition. The VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ data have been utilized to test the applicability of Graph theory. It has been observed that VE, $$\kappa_{{\rm S}}^{\text{E}}$$ and $$C_{{\rm P}}^{\text{E}}$$ values calculated from the Graph theory compare reasonably well with their corresponding experimental values. The Quantum mechanical calculations and IR spectral studies on the aforesaid mixtures support the presence of various molecular entities (estimated by analyses of VE data) in pure and mixed state.