The density (q), viscosity (g) and ultrasonic speed (U) of the pure solvents: 1,4-dioxane (DO), ethyl acetate (EA), tetrahydrofuran (THF) and solutions of the biologically active 1,1 0 -bis(3-methyl-4-ethoxyacetylphenoxy)cyclohexane were investigated at four temperatures: 298, 303, 308 and 313 K over a wide range of concentrations (0.1-0.01 molÁdm -3 ) to understand molecular interactions in these solutions. Various acoustical and thermodynamic parameters such as specific acoustical impedance (Z), isentropic (adiabatic) compressibility (j S ), Rao's molar sound function (R m ), van der Waals constant (b), internal pressure (p), free volume (V f ), intermolecular free path length (L f ), classical absorption coefficient {(a/f 2 ) Cl }, viscous relaxation time (s), Gibbs energy of activation (DG*), enthalpy of activation (DH*) and entropy of activation (DS*) were determined using the q, g and U data. A good to excellent correlation between a given parameter and concentration (C) is observed at all temperatures (T) and solvent systems studied. A linear increase or decrease of acoustical and thermodynamic parameters with concentration and temperature indicate the presence of strong molecular interactions in the solutions. DG* decreases linearly with increasing concentration and temperature in the DO system, while it decreases with C and increases with temperature in the EA and THF systems. The enthalpy of activation (DH*) was found to be practically independent of concentration but DH* and DS* were found to be slightly concentration dependent. In the DO system they are positive, while in the EA and THF systems they are negative.
Density (ρ), viscosity (η), ultrasonic speed (U), and thermo-acoustical parameters such as specific acoustical impedance (Z), adiabatic compressibility ( a ), internal pressure (π), free volume (V f ), inter molecular free path length (L f ), Van der Waals constant (b), viscous relaxation time (), classical absorption coefficient (α/f 2 ) cl , Rao's molar sound function (R m ), solvation number (S n ), Gibbs free energy of activation (ΔG*), enthalpy of activation (ΔH*) and entropy of activation (ΔS*) of biologically active 1,1'-bis(3-methyl-4-carboxyethylphenoxy)cyclohexane (BMCPC) in 1,4-dioxane (DO), ethyl acetate (EA), tetrahydrofuran (THF) have been studied at four different temperatures: 298, 303, 308 and 313 K to understand the molecular interactions in the solutions. A good to excellent correlation between a given parameter and concentration is observed at all temperatures and solvent systems studied. Linear increase or decrease [except (α/f 2 ) cl ] of acoustical parameters with concentration and temperature indicated the existence of strong molecular interactions. ΔG* decreased linearly with increasing concentration and temperature in DO and EA systems and increased with temperature in THF system. ΔH* and ΔS* are found practically concentration independent in case of DO and EA system but both are found concentration dependent in THF system
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