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The ultrasonic velocity ( U ), density (ρ) and viscosity (η) of solutions containing equimolar concentration of four cycloalkanones (cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone) and Tetrachloroethylene (TCE) in n -hexane solutions have been measured at five different temperatures in the range 293-313 K. Acoustical parameters such as adiabatic compressibility (β), Rao constant (R), absorption coefficient (α/ f 2 ), free energy of activation (Δ G *), internal pressure (π i ), cohesive energy (CE), free volume ( V f ), molecular interaction parameter with respect to ultrasonic velocity ( X u ), density ( X ρ ), and viscosity ( X η ) were calculated from the experimental data. Formation constant ( K ) values of the charge transfer (CT) complexes have been evaluated using a modified Bhat equation. Thermodynamic parameters such as free energy change (Δ G ), enthalpy change (Δ H ), and entropy change (Δ S ) for the formation of these complexes are computed from the variation of formation constant values with temperature. The stability constants of the charge transfer complexes formed between four cyclicketones and TCE correlate satisfactorily with polarisability (α), and ionization potential (IP) values of the ketones. [ABSTRACT FROM AUTHOR]

Abstract: Charge transfer complexes formed between iodine (acceptor) and six aromatic compounds, namely, benzene, pyrrole, thiophene, pyridine, quinoline and 2-methylquinoline (quinaldine) in n-hexane medium have been investigated by ultrasonic and UV–visible spectroscopic techniques at 303K. The measured values of ultrasonic velocity, density and viscosity were used to compute acoustical parameters and excess thermodynamic parameters. The trend in acoustical parameters with concentration identifies the existence of strong interactions amongst the solutes and the sign and magnitude of excess parameters establish the possibility of complex formation between the solute molecules. The specific interaction between the solutes is identified through the UV–visible spectra using Benesi–Hildebrand theory. The formation constants (K) of the charge-transfer complexes were determined by the Benesi–Hildebrand equation (spectroscopic method) and compared with those obtained by Kannappan method (ultrasonic). The trend in K values obtained by ultrasonic and spectral methods is similar and is explained with the structures of the donor molecules. [Copyright &y& Elsevier]

Abstract: Acoustical properties are computed for three ternary systems of aniline (ANI) and structurally different aromatic aldehydes, benzaldehyde (BA), cinnamaldehyde (CA) and salicylaldehyde (SA) in n-hexane medium from the measured ultrasonic velocity, density and dynamic viscosity at 303.15K and at atmospheric pressure. The trend in the acoustical parameters in the concentration range investigated confirmed complex formation through intermolecular hydrogen bonding between aldehyde and aniline. The formation constants (K) of the hydrogen bonded complexes are determined by ultrasonic method. The existence of strong aldehyde–amine interaction is also confirmed through electronic absorption spectra and the formation constants of these complexes are determined using Benesi–Hildebrand method at 303.15K. The values of K determined by ultrasonic and optical methods are comparable and follow similar trend. The trend in the formation constants is discussed based on structures of the component molecules and correlated with computed molecular properties. [Copyright &y& Elsevier]

The thermodynamic stability of complexes formed between N,N-dimethylaniline (DMANI) and three ketones, namely, acetophenone (ACP), 4-chloroactophenone (ClACP) and 4-methylacetophenone (MACP) in n-hexane is extensively investigated by spectral and ultrasonic methods. The ultrasound scan was carried out in the temperature range 208.15–313.15K and at atmospheric pressure on solutions containing equimolar concentrations of components ranging from 0.025 to 0.2M. The existence of solute–solute interactions has also been confirmed through electronic absorption spectra analyzed with Benesi-Hildebrand theory at 303.15K. The stability constants of the donor–acceptor complexes determined both by spectroscopic and ultrasonic methods are comparable and follow similar trends. The trend in the formation constants is discussed with structures of the components. The thermodynamic behavior of the systems was explained through the computed values of the free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) changes for complex formation are computed and discussed. [ABSTRACT FROM AUTHOR]

Abstract Physicochemical behaviour of n – hexane solutions containing benzyl amine (BA) and alicyclic ethers in the concentration range 0.02M–0.20 M is extensively studied through acoustical (experimental) and Density Functional Theory (DFT) methods and the nature of non-covalent molecular interactions existing in these ternary liquid mixtures have been investigated. Two structurally different ethers, namely, tetrahydrofuran (THF) and 1,4-dioxane (DIOX) are used. Ultrasonic velocity (u) at 2 MHz frequency, density (ρ) and viscosity (η) are measured for the ternary liquid systems at different concentrations andat 303.15 K. The existence of strong BA – ether non-covalent interaction and formation of hydrogen bonded complexes is identified in both the systems through the variations in acoustical and excess thermo-acoustical parameters with concentration. The influence of structure of ether on the strength of molecular interaction has been analysed through the calculation of formation constants of these complexes computed using Kannappan equation. An attempt has been made using meta hybrid density functional theory to confirm the existence of hydrogen bonded complexes in these two systems through the computed interaction energies and hydrogen bonding parameters. Computational investigation shows CH---π dispersive interactions in these complexes in addition to the classical hydrogen bonding. Graphical abstract Image 1 Highlights • Acoustical study was done on ternary systems of benzyl amine and alicyclic ethers. • Formation constants of H- bonded complexes are reported. • DFT study shows CH---π interaction in addition to classical H – bonding. • Interaction parameters are used to assess the strength of various interactions. • The structural dependence of ethers on the stability of complexes is discussed. [ABSTRACT FROM AUTHOR]

The existence of non-covalent interactions between iodine and three haloarenes, namely, fluorobenzene ( FB ), bromobenzene ( BB ) and iodobenzene ( IB ) with iodine in n-hexane medium at 303 K was established from the trend in acoustical properties and excess thermo acoustical parameters with concentration. Formation constants of the three ternary mixtures were determined by a novel ultrasonic method employing the equation proposed by Kannappan. The trend in K values of the three complexes agreed well with the trend obtained by spectral methods by earlier workers. Dispersion and long-range corrected ω-B97X-D3 functional was used to calculate the both π and halogen bonded types of interactions. NBO analyses were used to quantify the nature of the stabilizing interactions that exist in the complexes of haloarenes with I 2 . Our computed results are in good agreement with the observations in ultrasonic method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Role of aromatic ring in the formation of H-bonded complexes of cyclohexanone (CHE) is analyzed by ultrasonic. • Excess parameters predict strong interactions in aromatic hydroxyl and amine systems with CHE. • Intermolecular H-bond is established in these systems by UV–vis and IR spectra. • Theoretical analysis reveals existence of stronger O H...O and C H...O interactions in systems containing aromatic ring. • NCI and RDG plots established the presence of non-covalent interactions besides H-bond in these systems. The existence of intermolecular hydrogen bonded interaction between four structurally hydroxyl and amino compounds namely, phenol (PHE) , aniline (ANI) , cyclohexanol (CHL) and cyclohexylamine (CHA) with cyclohexanone (CHE) was investigated in n -hexane medium at 303 K by experimental methods (ultrasonic, UV–Visible, IR spectral analysis) and theoretical (DFT, NCI) methods. From the acoustical and excess thermo-acoustical parameters, strong solute–solute interactions of hydrogen bonded type between the solutes were established. The formation of 1:1complexes between cyclohexanone and hydroxyl, amino compounds was confirmed by UV–visible spectral method and the presence of hydrogen bonding in these complexes was proved by IR spectrum. The stability constant of the four hydrogen bonded complexes was calculated by both ultrasonic and UV–Visible spectroscopic methods. Interestingly, it was found that the order of strength of hydrogen bonding between CHE and hydroxyl as well as amino compounds is in the order CHE-PHE > CHE-ANI > CHE-CHL > CHE-CHA. DFT calculations, NBO analysis and NCI plots were also made to quantify the nature of stabilizing interactions between CHE and hydroxyl and amino compounds. Our computed results are in good agreement with the experimental observations. It is observed that aromatic moiety adjacent to hydrogen donor influences significantly the stability of the H-bonded complexes. [ABSTRACT FROM AUTHOR]

Abstract: Viscometric and ultrasonic studies have been carried out in n-hexane solutions, containing equimolar concentration from 0.02 to 0.2M of aromatic ketones and N-methylaniline (NMANI), at 303.15K and at atmospheric pressure. The ketones studied in the present investigation are acetophenone (ACP), 4-chloroacetophenone (ClACP) and 4-methylacetophenone (MACP). The behaviour of measured ultrasonic velocity (u), density (ρ) and viscosity (η) and also the computed acoustic parameters provide strong evidence for the presence of strong solute–solute interactions in the three ternary systems. Excess molar volume and excess thermo acoustic parameters reveal the existence of hydrogen bonded complexes between the solute molecules, ketones and secondary amine. The variation of these parameters with the concentration shows that the existing interactions are influenced by the structure of components and functional groups of the components involved. An attempt has been made to confirm the formation of 1:1 complexes in these systems through UV–visible spectroscopic method at 303.15K. The calculated values of formation constants of the charge transfer complexes both by acoustic and optical methods agree satisfactorily. The variation in the values of formation constant reveals that electron releasing substituent in the acetophenone molecule enhances the stability while electronegative substituent decreases the stability of the complex. The negative values of free energy of formation of these three complexes indicate that these complexes are thermodynamically stable. [Copyright &y& Elsevier]

Experimental (acoustical) and theoretical (DFT) analyses have been undertaken to unravel the possibility of hydrogen bonded complexes of isopropylamine (IPA) with two industrially important cyclic ethers, tetrahydrofuran (THF) and 1,4 dioxane (DIOX) in n – hexane at 303.15 K and at atmospheric pressure. The trend in acoustical and excess parameters with concentration revealed the dominance of structure breaking behavior of like molecules of solute components and formation of intermolecular H-bonding between IPA and ethers in the two ternary systems at room temperature. The data obtained through DFT studies further support the existence of intermolecular H-bond between amine and ethers. The strength of interactions has been assessed from the formation constants (K) determined by acoustic method and interaction energies by DFT respectively. The reduced density gradient (RDG) and non-covalent interaction (NCI) plots clearly exhibit the presence of intermolecular interactions in the two systems. The stability of these complexes and the strength of the interactions are explained with the structure of ether. Comparison of K and interaction energy values in the present study with those obtained in n-propylamine interactions with ethers showed steric effect in the formation of complex of IPA with the two ethers. Unlabelled Image • H-bonded interaction of isopropylamine with two alicyclic ethers was identified. • Stability of complexes was analysed through ultrasonic and DFT methods. • DFT study shows the interaction is through inter molecular hydrogen bond. • Formation constant and interaction energy values revealed presence of weak interaction. • Comparison of results in NPA and IPA interactions with ethers showed the steric effect. [ABSTRACT FROM AUTHOR]

The structure breaking behavior in n-propyl amine (NPA) and formation of hydrogen bonded complexes between NPA and two industrially important cyclic ethers, tetrahydrofuran (THF) and 1,4 dioxane (DIOX) are analyzed through ultrasonic velocity (u), density (ρ) and viscosity (η) measurements in n – hexane medium at 303.15 K and at atmospheric pressure. Various acoustical and excess thermo-acoustical parameters are computed and their variations with concentration confirmed the presence of relatively strong intermolecular interactions between amine and ether molecules. Stability constants (K) of these complexes are determined by ultrasonic method to assess the strength of the interactions. Extensive DFT analysis is carried out on the optimized geometry of the component molecules and also their complexes in n -hexane. Computed hydrogen bond parameters support the observations made in experimental ultrasonic investigations. NCI and RDG plots for the complexes are discussed in the light of possible non covalent interactions. Image 1 • Ultrasonic study was done on the systems of n – propylamine with alicylic ethers in n -hexane. • Stability constants (K) for the complexesdetermined by ultrasonic method are reported. • DFT study shows presence of H-bond and other non-covalent interactions in the systems. • Interaction energy and structural parameters correlate with experimental K values. • NCI and RDG plots confirm the presence of H-bonding and other interactions. [ABSTRACT FROM AUTHOR]