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Mixtures involving nitrobenzene and hydrocarbons, or 1-alkanols and 1-nitroalkane, or nitrobenzene have been investigated based on a whole set of thermophysical properties available in the literature: excess molar functions (enthalpies, entropies, isobaric heat capacities, and volumes), vapour-liquid and liquid-liquid equilibria, permittivities or dynamic viscosities. In addition, the mixtures have been studied by means of the DISQUAC, ERAS, and UNIFAC models, and the concentration-concentration structure factor. The corresponding DISQUAC and ERAS interaction parameters are reported. In alkane mixtures, dipolar interactions between 1-nitroalkane molecules are weakened when the size of the polar compound increases, accordingly with the relative variation of their effective dipolar moment. Dipolar interactions are stronger in nitrobenzene solutions than in those containing the smaller 1-nitropropane, although both nitroalkanes have very similar effective dipole moment (aromaticity effect). Systems with 1-alkanols are characterized by dipolar interactions between like molecules which sharply increases when the alkanol size increases. Simultaneously, interactions between unlike molecules become weaker, as the OH group is then more sterically hindered. Interactions between unlike molecules are stronger in systems with nitromethane than in nitrobenzene solutions. The replacement of nitromethane by nitroethane in systems with a given 1-alkanol leads to strengthen those effects related with the alcohol self-association. Permittivity data and results on Kirkwood correlation factors show that the addition of 1-alkanol to a nitroalkane leads to cooperative effects, which increase the dipolar polarization of the solution, in such way that the destruction of the existing structure in pure liquids is partially counterbalanced. This effect is less important when longer 1-alkanols are involved.

The liquid-liquid equilibrium (LLE) curves have been determined for the 2-hydroxyl-benzaldehyde (salicylaldehyde, SAC) + CH$_3$(CH$_2$)$_n$CH$_3$ mixtures ($n$ = 5,6,7,8,9). The equilibrium temperatures were determined observing, by means of a laser scattering technique, the turbidity produced on cooling when a second phase takes place. All the systems show an upper critical solution temperature, which linearly increases with $n$. Intermolecular effects have been investigated in alkanol + benzaldehyde systems using data from the literature. Interactions in 1-alkanol mixtures are mainly of dipolar type. The corresponding excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, are large and positive, which reveals that interactions between like molecules are dominant. Interactions between unlike molecules are stronger for the methanol-containing system. For the other mixtures, the enthalpy of the (1-alkanol)-benzaldehyde interactions remains more or less constant. At 298.15 K and equimolar composition, the replacement of a linear polar solvent by the isomeric aromatic one leads to increased $H_{\text{m}}^{\text{E}}$ values in systems with a given 1-alkanol. The phenol + benzaldehyde system shows strongly negative deviations from the Raoult's law. Proximity effects have been examined in SAC + hydrocarbon mixtures. Alkane-containing systems are essentially characterized by dipolar interactions, while dispersive interactions are prevalent in the solution with benzene. All the mixtures have been treated in terms of DISQUAC. The interaction parameters for the OH/CHO contacts and for the SAC/aromatic and SAC/alkane contacts have been reported. DISQUAC provides a correct description of the thermodynamic properties considered. In the case of SAC systems, this is done by defining a new specific group HO-C-C-CHO for salicylaldehyde.

The coexistence curves of liquid-liquid equilibrium (LLE) for the mixtures: phenylacetonitrile + heptane, + octane, + nonane, + cyclooctane, or + 2,2,4-trimethylpentane and for 3-phenylpropionitrile + heptane, or + octane are reported. Aromatic nitrile + alkane, + aromatic hydrocarbon or + 1 alkanol systems are investigated using a set of thermophysical properties: phase equilibria (solid-liquid, SLE, vapour-liquid, VLE and LLE), excess molar functions, enthalpies ($H_{\text{m}}^{\text{E}}$), isochoric internal energies, isobaric heat capacities ($C_{p \text{m}}^{\text{E}}$) and volumes ($V_{\text{m}}^{\text{E}}$), and the Kirkwood correlation factor. Due to proximity effects between the phenyl and the CN groups, dipolar interactions between molecules of aromatic nitriles are stronger than those between molecules of isomeric linear nitriles. Dipolar interactions become weaker in the order: 3-phenylpropionitrile > phenylacetonitrile > benzonitrile. Benzonitrile + aromatic hydrocarbon mixtures are characterized by dispersive interactions and structural effects. The latter are more important in systems with phenylacetonitrile. Structural effects are also present in benzonitrile + n-alkane, or + 1-alkanol + mixtures. The systems mentioned above have been studied using DISQUAC. Interaction parameters for contacts where the CN group in aromatic nitriles participates are given and DISQUAC results on excess properties and phase equilibria are discussed. 1-Alkanol + benzonitrile mixtures are also investigated by means of the ERAS model. ERAS represents well $H_{\text{m}}^{\text{E}}$ of these systems. The $V_{\text{m}}^{\text{E}}$ curves of solutions with longer 1-alkanols are more poorly described, which has been explained in terms of the existence of structural effects.

Interactions and structure of organic carbonate + alkane, and 1-alkanol + organic carbonate mixtures have been investigated by means of a set of molar excess functions: enthalpies, volumes, isobaric heat capacities, or entropies; and considering internal pressure, liquid-liquid equilibria or permittivity data. In addition, the mentioned systems have been studied using the Flory model and the concentration-concentration structure factor formalism. The mixtures under consideration are characterized by dipolar interactions and by homocoordination (that is, by interactions between like molecules). In systems with a given solvent, dipolar interactions are weakened in the order: propylene carbonate (PC) > dimethyl carbonate (DMC) > diethyl carbonate (DEC). Comparison of mixtures containing DMC or DEC with those involving 2-propanone or 3-pentanone shows that dipolar interactions are not determined merely by values of the dipole moment, but they also depend on the group size. The enthalpies of the alkanol-carbonate interactions have been evaluated from calorimetric data. They are stronger in DMC solutions and become weaker when the alcohol size increases in mixtures with a given carbonate. Application of the Flory model to 43 systems of the type 1-alkanol + carbonate provides a mean relative standard deviation for excess molar enthalpy equal to 0.107. Results reveal that orientational effects decrease in the order DEC > PC > DMC. Orientational effects are particularly relevant in methanol or ethanol + DEC mixtures. Interestingly, the mentioned effects are weaker in 1-alkanol + DMC mixtures than in DMC + alkane systems. A similar trend is observed in DEC solutions when the considered alcohol is longer than ethanol.

Relative permittivities at 1 MHz, $\varepsilon_{\text{r}}$, and refractive indices at the sodium D-line, $n_{\text{D}}$, are reported at 0.1 MPa and at (293.15-303.15) K for the binary systems 1-alkanol + n-hexylamine (HxA). Also, their corresponding excess functions are calculated and correlated. Positive values of the excess permittivities, $\varepsilon_{\text{r}}^{\text{E}}$, are encountered for the methanol system, whereas the remaining mixtures show negative values. This reveals that interactions between unlike molecules contribute positively to $\varepsilon_{\text{r}}^{\text{E}}$. This contribution is dominant for the methanol mixture, while those arising from the breaking of interactions between like molecules are prevalent for the remaining mixtures. At ${\phi}_1$ (volume fraction) = 0.5, $\varepsilon_{\text{r}}^{\text{E}}$ changes in the order: methanol > 1-propanol > 1-butanol > 1-pentanol < 1-heptanol. Similar variation with the chain length of the 1-alkanol is observed for mixtures such as 1-alkanol + heptane, or + cyclohexylamine, and can be explained in terms of the lower and weaker self-association of longer 1-alkanols. The effect of the replacement of HxA by cyclohexylamine, or by aniline, is also shown. Calculations on molar refractions indicate that dispersive interactions in the systems under study increase with the length of the 1-alkanol. The mixtures are studied by means of the application of the Kirkwood-Fr\"ohlich model, and the Kirkwood correlation factors, including the corresponding excess values, are reported.

Data on density, $\rho$, speed of sound, $c$, and refractive index, $n_{\text{D}}$, have been reported at (293-303.15) K for the N,N-dimethylacetamide (DMA) + CH$_3$CO(CH$_2$)$_{u-1}$CH$_3$ ($u$ = 1, 2, 3) systems, and at 298.15 K for the mixture with $u$ = 5. These data have been used to compute excess molar volumes, $V_{\text{m}}^{\text{E}}$, excess adiabatic compressibilities, $\kappa_S^{\text{E}}$, and excess speeds of sound $c^{\text{E}}$. Negative $V_{\text{m}}^{\text{E}}$ values indicate the existence of structural effects and interactions between unlike molecules. From excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, available in the literature for N,N-dimethylformamide (DMF), or N-methylpyrrolidone (NMP) + n-alkanone systems, it is shown: (i) amide-ketone interactions are stronger in DMF systems than in those with NMP; (ii) they become weaker when $u$ increases in mixtures with a given amide. Structural effects largely contribute to $H_{\text{m}}^{\text{E}}$ and are more relevant in mixtures containing NMP. The application of the Flory's model reveals that the random mixing hypothesis is valid to a large extent for DMF solutions, while NMP systems are characterized by rather strong orientational effects. From values of molar refraction and of the product $P_{\text{int}} V_{\text{m}}$ (where $P_{\text{int}}$ is the internal pressure and $V_{\text{m}}$ the molar volume), it is concluded that dispersive interactions increase with $u$, or when DMF is replaced by DMA in mixtures with a fixed ketone.

Interactions and structure of alkanone, or alkanal or dialkyl carbonate + alkane mixtures, or of 2-alkanone+ 2-alkanone, or of ketone + dialkyl carbonate systems have been investigated by means of a set of thermodynamic properties and by the application of the Flory model. The properties considered are excess molar quantities: enthalpies, $H_{\text{m}}^{\text{E}}$, volumes, $V_{\text{m}}^{\text{E}}$, or isobaric heat capacities, $C_{p \text{m}}^{\text{E}}$, and liquid-liquid equilibria. Experimental data show that alkane mixtures are characterized by rather strong dipolar interactions. In the case of systems containing ketones with the same number of C atoms and a given alkane, dipolar interactions become weaker in the sequence: aromatic > cyclic > linear. In addition, the mentioned interactions become also weaker in the order: dialkyl carbonate > linear alkanone > linear alkanal. This is an important result, as carbonates show lower effective dipole moments than the other compounds, and it suggests that the group size may be relevant when evaluating thermodynamic properties of liquid mixtures. Results on $H_{\text{m}}^{\text{E}}$ from the Flory model show that orientational effects (i.e., non-random mixing) are rather similar for systems with linear, cyclic or aromatic ketones or alkanals and alkanes. In contrast, orientational effects become weaker in dialkyl carbonate + alkane mixtures. The behaviour of 2-alkanone + 2-alkanone systems and of mixtures of longer 2-alkanones or cyclohexanone with dialkyl carbonate is close to random mixing. Larger orientational effects are encountered in solutions of carbonates and shorter 2-alkanones.

Liquid-liquid equilibrium (LLE) phase diagrams have been determined, by means of the critical opalescence method with a laser scattering technique, for the mixtures 4-phenylbutan-2-one + CH$_3$(CH$_2$)$_n$CH$_3$ ($n = 10,12,14$) and for benzyl ethanoate + CH$_3$(CH$_2$)$_n$CH$_3$ ($n = 12,14$). The systems are characterized by having an upper critical solution temperature (UCST), which increases with n. The corresponding LLE curves show a rather horizontal top and become skewed toward higher mole fractions of the polar compound when n is increased. Calorimetric and LLE measurements show that, for mixtures with molecules with a given functional group, interactions between aromatic molecules are stronger than those between homomorphic linear molecules (aromaticity effect). This has been ascribed to proximity effects arising from the presence of the polar group and the aromatic ring within the same molecule. Proximity effects become weaker in the sequence 1-phenylpropan-2-one > 4-phenylbutan-2-one > 1-phenylethanone and are more important in benzyl ethanoate than in ethyl benzoate molecules. Values of the critical compositions and temperatures calculated with the DISQUAC group contribution model are in good agreement with the experimental results. Accordingly, the shape of the LLE curves is also correctly described by DISQUAC.

Densities, $\rho$, speeds of sound, $c$, and refractive indices, $n_{\text{D}}$, have been measured for the systems N,N-dimethylformamide (DMF) + propanone, + 2-butanone, or + 2-pentanone in the temperature ($T$) range from 293.15 to 303.15 K and at 298.15 K for the DMF + 2-heptanone mixture. Due to the high volatility of acetone, the corresponding $n_{\text{D}}$ measurements were developed at 293.15 K and 298.15 K. The direct experimental data were used to determine the excess molar volumes, $V_{\text{m}}^{\text{E}}$, and the excess refractive indices, $n_{\text{D}}^{\text{E}}$, at the working $T$. Values of the excess functions at 298.15 K, for the speed of sound, $c^{\text{E}}$, the isentropic compressibility, $\kappa_S^{\text{E}}$ and for the excess thermal expansion coefficient, $\alpha_p^{\text{E}}$, were also calculated. The investigated systems are characterized by strong amide-ketone interactions, which become weaker when the alkanone size is increased. This is supported by negative $V_{\text{m}}^{\text{E}}$ values; by the dependence on $T$ and pressure of $V_{\text{m}}^{\text{E}}$, and by positive $P_{\text{int}}^{\text{E}}$ (excess internal pressure) values. Analysis of the systems in terms of the Rao's constant indicates that there is no complex formation. In addition, negative $V_{\text{m}}^{\text{E}}$ values also reveal the existence of structural effects, which largely contribute to the excess molar enthalpy, $H_{\text{m}}^{\text{E}}$. $V_{\text{m}}^{\text{E}}$ and $H_{\text{m}}^{\text{E}}$ values increase with the chain length of the 2-alkanone. It allows to conclude that the relative $V_{\text{m}}^{\text{E}}$ variation with the ketone size is closely related to that of the interactional contribution to this excess function. Molar refraction values, $R_{\text{m}}$, show that dispersive interactions become more relevant for the systems including longer 2-alkanones.

1-Alkanol + alkanenitrile systems have been studied by means of the DISQUAC, ERAS and UNIFAC (Dortmund) models. DISQUAC and ERAS parameters for the alkanol/nitrile interactions are reported. DISQUAC describes a whole set of thermodynamic properties: phase equilibria, vapour-liquid (VLE), liquid-liquid (LLE) and solid-liquid (SLE) equilibria, molar excess functions, Gibbs energies, $G_{\text{m}}^{\text{E}}$, and enthalpies, $H_{\text{m}}^{\text{E}}$, and partial excess molar enthalpies at infinite dilution, $H_{\text{mi}}^{\text{E,}\infty }$ using the same set of interaction parameters for each solution. The dependence on the molecular structure of the interaction parameters is similar to that observed in other previous applications to mixtures formed by 1-alkanols and a strongly polar compound, in such way that the quasichemical interchange coefficients can be kept constant from 1-propanol. However, methanol and ethanol solutions behave differently. From the analysis of experimental data for $H_{\text{m}}^{\text{E}}$, $TS_{\text{m}}^{\text{E}}(=H_{\text{m}}^{\text{E}}-G_{\text{m}}^{\text{E}})$, and molar excess volumes, $V_{\text{m}}^{\text{E}}$, it is concluded that the studied systems are characterized by dipolar interactions and strong structural effects. The former are more relevant in acetonitrile solutions. Association effects are more important in butanenitrile mixtures. DISQUAC improves $H_{\text{m}}^{\text{E}}$ results from the ERAS model. ERAS results on $H_{\text{m}}^{\text{E}}$ for systems containing acetonitrile are also improved by UNIFAC. This remarks the importance of dipolar interactions in the investigated mixtures. ERAS describes the variation of $V_{\text{m}}^{\text{E}}$(${{x}_{1}}$=0.5) with the 1-alkanol size for mixtures with a given nitrile, but the concentration dependence of this excess function is poorly represented.