Orientational and steric effects in linear alkanoates + N-Alkane mixtures

Abstract

The CH$_3$(CH$_2$)$_u$COO(CH$_3$)$_v$CH$_3$ + n-alkane mixtures have been investigated on the basis of an experimental database containing effective dipole moments of esters, and excess molar functions of the systems: enthalpies ($H_{\text{m}}^{\text{E}}$), volumes ($V_{\text{m}}^{\text{E}}$), isobaric heat capacities ($C_{p\text{m}}^{\text{E}}$) and isochoric internal energies ($U_{V\text{m}}^{\text{E}}$) and by means of the application of the Flory model and the Kirkwood-Buff formalism. The situation of the mixtures within the $G_{\text{m}}^{\text{E}}$ (excess molar Gibbs energy) vs. $H_{\text{m}}^{\text{E}}$ diagram has also been briefly considered. Results indicate that dispersive interactions are dominant and that steric effects can explain some differences between solutions containing heptane and isomeric esters. Proximity and orientational effects are also discussed in diester + hexane mixtures. In the case of systems with a given alkane and different isomeric polar compounds, orientational effects become weaker in the order: n-alkanone > dialkyl carbonate > n-alkanoate. Results from the Kirkwood-Buff formalism indicate that the number of ester-ester interactions decreases in systems with alkyl ethanoates when the alkyl size increases and that preferential solvation between polar molecules decreases as follows: dialkyl carbonate > n-alkanone > n-alkanoate.