Topological investigations on the association of alkanols: excess volume of pyridine–alkanol (C1–C10) mixtures

Abstract

The excess volume (V^E) has been determined dilatometrically for 10 binary pyridine–alkanol mixtures over the whole composition range at 298.15 K. The V^E values were negative for pyridine–alkanol (C₁–C₆) mixtures, sigmoid for pyridine–heptanol mixtures (with negative V^E values at lower mole fractions of pyridine) and positive for pyridine–alkanol (C₈–C₁₀) mixtures over the complete mole fraction range. V^E values increased in a positive direction with increase in chain length of the alkanol (C₁–C₁₀). Experimental V^E data have been analysed in terms of graph theory which utilises the concept of the third-degree molecular connectivity index. The results obtained from graph theory have been used to predict the association of pyridine and alkanols in the pure and mixed states.

The V^E data have also been analysed using the Prigogine–Flory–Patterson theory. An analysis of each of the three contributions viz. interactional, free volume and P* to V^E shows that the interactional contribution and the free volume effects are negative for all systems, whereas the P* contribution is negative for methanol and ethanol and positive for remainder of the alkanols.