Structural effect on the strength of non-covalent interactions in binary mixtures of benzyl amine and certain ethers through ultrasonic, FT-IR spectral and DFT studies at 303.15 K

Abstract Ultrasonic velocities (u), densities (ρ) and viscosities (η) of four binary liquid mixtures, containing benzyl amine (BA) as common component and four structurally different ethers (tetrahydrofuran (THF), 1,4 dioxane (DIOX), anisole (ANI) and diphenyl ether (DPE)) as varying components, were measured over the entire mole fraction range at 303.15 K and at experimental pressure of 101 kPa. The experimental data were used to compute several acoustical and excess thermodynamic parameters. The computed excess thermo-acoustic properties for each binary mixture are fitted to Redlich–Kister type polynomial equation. The computed binary co-efficients and standard deviations between the experimental and theoretical values established the existence of specific interactions in the complexes of four systems. The acoustical and excess thermo acoustic parameters were analysed in light of various types of intermolecular interactions and their structural dependence. The influence of structures of ethers on the non-covalent molecular interactions has been attempted through Density Functional Theory (DFT) calculation. The optimized structures of the monomers (BA, THF DIOX, ANI, and DPE), their self associated dimers (BA-BA, THF-THF, DIOX-DIOX, ANI-ANI and DPE-DPE) and their complexes with BA confirm the presence of hydrogen bonded interactions in all the four systems. In addition to the classical hydrogen bonding, CH⋯π interactions have also been identified in the binary systems which influenced the interaction energies of the complexes. The presence of non-covalent interactions among the solute species is supported by FTIR spectra of pure compounds and binary mixtures. The shift in the frequencies of the functional groups of amine and ethers has confirmed the observations made through ultrasonic and DFT studies.